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SD-01-333

Bendix® Tu-Flo® 550 Air Compressor

BENDIX® TU-FLO® 550 AIR COMPRESSOR

(CROSS SECTION)

BENDIX® TU-FLO® 550 AIR COMPRESSOR

(EXTERIOR)

AIR DISCHARGE WATER OUTLET

PIECE NO.

TAG

GOVERNOR

MOUNTING

PAD

CRANKCASE

PISTON RINGS

PISTON

CRANKSHAFT

CONNECTING

ROD

INLET VALVE

SEAT

UNLOADER

INLET VALVE

CYLINDER

HEAD

END VIEW OF CYLINDER HEAD

DISCHARGE

VALVE SPRING

DISCHARGE

VALVE

DISCHARGE

VALVE STOP

AIR INLET

CRANKCASE

INLET

INLET VALVE

SPRING

DESCRIPTION

The function of the air compressor is to provide and

maintain air under pressure to operate devices in the air

brake and/or auxiliary air systems. The Bendix® Tu-Flo® 550

compressor is a two cylinder single stage, reciprocating

compressor with a rated displacement of 13.2 cubic feet

per minute at 1250 RPM.

The compressor assembly consists of two major

subassemblies, the cylinder head and the crankcase. The

cylinder head is an iron casting which houses the inlet,

discharge, and unloader valving. (See Figure 1.) The

cylinder head contains the air inlet port and is designed

with both top and side air discharge ports. Three water

coolant ports provide a choice of coolant line connections.

Governor mounting surfaces are provided at both the front

and the rear of the cylinder head. The head is mounted

on the crankcase and is secured by six cap screws. The

Tu-Flo® 550 compressor is designed such that the cylinder

head can be installed in one of two positions which are 180

degrees apart. The crankcase houses the cylinder bores,

pistons, crankshaft and main bearings, and provides the

ﬂ ange or base mounting surface.

DISCHARGE

VALVE SEAT

UNLOADER

COVER

WATER

INLET

OPERATION

The compressor is driven by the vehicle engine and

is operating continuously while the engine is running.

Actual compression of air is controlled by the compressor

unloading mechanism and the governor. The governor

which is generally mounted on the compressor maintains

the brake system air pressure to a preset maximum and

minimum pressure level.

INTAKE AND COMPRESSION OF AIR (LOADED)

During the down stroke of the piston, a slight vacuum is

created between the top of the piston and the cylinder head,

causing the inlet valve to move off its seat and open. (Note:

The discharge valve remains on its seat.) Atmospheric air

is drawn through the air strainer and the open inlet valve

into the cylinder (see Figure 4). As the piston begins its

upward stroke, the air that was drawn into the cylinder on

the down stroke is being compressed. Air pressure on the

inlet valve plus the force of the inlet spring, returns the

inlet valve to its seat and closes. The piston continues the

upward stroke and compressed air pushes the discharge

valve off its seat and air ﬂ ows by the open discharge valve,

into the discharge line and to the reservoirs (see Figure 5).

As the piston reaches the top of its stroke and starts down,

the discharge valve spring and air pressure in the discharge

line returns the discharge valve to its seat. This prevents

the compressed air in the discharge line from returning to

the cylinder bore as the intake and compression cycle is

repeated.

CAT MACK

(MACK STYLE)

DETROIT

DIESEL

AIR INLET

WATER

UNLOADER COVER

PLATE

AIR DISCHARGE

WATER

AIR

DISCHARGE

GOVERNOR

WATER

MANUFACTURED BY BENDIX

TU-FLO® 550 COMPRESSOR

BENDIX NO.

SERIAL NO.

MACK

"FOXHEAD"

CUMMINS

MACK

EXTENDED

FIGURE 2 - FLANGE CONFIGURATIONS

Various mounting and drive conﬁ gurations, as shown in

Figure 2, are supplied as required by the vehicle engine

designs. A nameplate identifying the compressor piece

number and serial number is attached to the side of the

crankcase. (Reference Figure 3.)

FIGURE 3 - NAMEPLATE

FIGURE 1 - CYLINDER HEAD

CAT BASE

MOUNT

force the pistons upward and the inlet valves return to their

seats. Compression is then resumed.

COMPRESSOR & THE AIR BRAKE SYSTEM

GENERAL

The compressor is part of the total air brake system, more

speciﬁ cally, the charging portion of the air brake system.

As a component in the overall system its condition, duty

cycle, proper installation and operation will directly affect

other components in the system.

the air pressure for the air brake system. The air compressor

is typically cooled by the engine coolant system, lubricated

by the engine oil supply and has its inlet connected to the

engine induction system.

As the atmospheric air is compressed, all the water vapor

originally in the air is carried along into the air system, as

well as a small amount of the lubricating oil as vapor. If an

air dryer is not used to remove these contaminants prior

to entering the air system, the majority, but not all, will

condense in the reservoirs. The quantity of contaminants

that reach the air system depends on several factors

including installation, maintenance and contaminant

handling devices in the system. These contaminants must

either be eliminated prior to entering the air system or after

they enter.

DUTY CYCLE

The duty cycle is the ratio of time the compressor spends

building air to the total engine running time. Air compressors

are designed to build air (run "loaded") up to 25% of the

time. Higher duty cycles cause conditions that affect air

GOVERNOR

PORT

AIR

INLET

PORT

INLET

VALVE

OPEN

PISTON

MOVING

DOWN

DISCHARGE

VALVE

CLOSED

GOVERNOR

PORT

INLET

VALVE

CLOSED

PISTON

MOVING

FIGURE 4 - OPERATIONAL-LOADED (INTAKE)

FIGURE 5 - OPERATIONAL-LOADED (COMPRESSION)

GOVERNOR

PORT

DISCHARGE

PORT

AIR

INLET

PORT

FIGURE 6 - OPERATIONAL-UNLOADED

DISCHARGE

VALVE

CLOSED

DISCHARGE

VALVE

OPEN

AIR

INLET

PORT

NON-COMPRESSION OF AIR (UNLOADED)

When air pressure in the reservoir reaches the cut-out

setting of the governor, the governor allows air to pass

from the reservoir, through the governor and into the cavity

above the unloader pistons. The unloader pistons move

down holding the inlet valves off their seats (see Figure

6.)

With the inlet valves held off their seats by the unloader

pistons, air is pumped back and forth between the two

cylinders, and the discharge valves remain closed. When

air pressure from the reservoir drops to the cut-in setting

of the governor, the governor closes and exhausts the air

from above the unloader pistons. The unloader springs

INLET VALVE

HELD OPEN

BY UNLOADER

PISTON

AIR

DISCHARGE

PORT

AIR

DISCHARGE

PORT

UNLOADER

PISTON

brake charging system performance which may require

additional maintenance. Factors that add to the duty cycle

are: air suspension, additional air accessories, use of an

undersized compressor, frequent stops, excessive leakage

from ﬁ ttings, connections, lines, chambers or valves, etc.

Refer to Table A in the Troubleshooting section for a guide

to various duty cycles and the consideration that must be

given to maintenance of other components.

COMPRESSOR INSTALLATION

While the original compressor installation is usually

completed by the vehicle manufacturer, conditions of

operation and maintenance may require additional

consideration. The following presents base guidelines.

DISCHARGE LINE

The discharge line allows the air, water-vapor and oil-vapor

mixture to cool between the compressor and air dryer or

reservoir. The typical size of a vehicle's discharge line,

(see column 2 of Table A in the Troubleshooting section)

assumes a compressor with a normal (less than 25%) duty

cycle, operating in a temperate climate. See Bendix and/or

other air dryer manufacturer guidelines as needed.

The discharge line must maintain a constant slope down

from the compressor to the air dryer inlet ﬁ tting or reservoir

to avoid low points where ice may form and block the ﬂ ow.

If, instead, ice blockages occur at the air dryer or reservoir

inlet, insulation may be added here, or if the inlet ﬁ tting is

a typical 90 degree ﬁ tting, it may be changed to a straight

or 45 degree ﬁ tting. Shorter discharge line lengths or

insulation may be required in cold climates.

While not all compressors and charging systems are

equipped with a discharge line safety valve this component

is recommended. The discharge line safety valve is

FIGURE 6A - SYSTEM DRAWING

FIGURE 6B - DISCHARGE LINE SAFETY VALVE

HOLE

THREAD

installed in the cylinder head (Tu-Flo® 550/750) or close to

the compressor discharge port and protects against over

pressurizing the compressor in the event of a discharge

line freezeup.

DISCHARGE LINE TEMPERATURE

When the temperature of the compressed air that enters

the air dryer is within the normal range, the air dryer can

remove most of the charging system oil. If the temperature

of the compressed air is above the normal range, oil as

oil-vapor is able to pass through the air dryer and into the

air system. Larger diameter discharge lines and/or longer

discharge line lengths can help reduce the temperature.

The air dryer contains a ﬁ lter that collects oil droplets, and

a desiccant bed that removes almost all of the remaining

water vapor. The compressed air is then passed to the air

brake service (supply) reservoir. The oil droplets and the

water collected are automatically purged when the governor

reaches its "cut-out" setting.

Air Dryer

Reservoir Drain

Service Reservoir

(Supply Reservoir)

Compressor

Governor

(Governor plus Synchro valve

for the Bendix® DuraFlo™ 596

Compressor)

Discharge

Line Optional “Ping” Tank

Optional Bendix® PuraGuard QC™

Oil Coalescing Filter

The Air Brake Charging System supplies the

compressed air for the braking system as well as other air

accessories for the vehicle. The system usually consists

of an air compressor, governor, discharge line, air dryer,

and service reservoir.

FIGURE 7 - LUBRICATION

OIL

INLET

2. Naturally aspirated Engine Air Cleaner - Compressor

inlet is connected to the engine air cleaner or the

vacuum side (engine air cleaner) of the supercharger

or turbocharger.

3. Pressurized induction - Compressor inlet is

connected to the pressure side of the supercharger or

turbocharger.

See the tabulated technical data on page 14 of this manual

for speciﬁ c requirements for numbers 2 and 3 above.

If a previously unturbocharged compressor is being

turbocharged, it is recommended that the inlet cavity screen

(238948) be installed with an inlet gasket (291909) on both

sides of the screen.

WATER

(1 PORT

ONLY)

WATER

OUT

(1 PORT

ONLY)

WATER OUT

WATER

OUT

WATER

FIGURE 8 - COOLING

For vehicles with accessories that are sensitive to small

amounts of oil, we recommend installation of a Bendix®

PuraGuard® QC™ oil coalescing ﬁ lter, designed to minimize

the amount of oil present.

LUBRICATION

The vehicle's engine provides a continuous supply of oil

to the compressor. Oil is routed from the engine to the

compressor oil inlet. An oil passage in the compressor

crankshaft allows oil to lubricate the connecting rod

crankshaft bearings. Connecting rod wrist pin bushings

and crankshaft ball bearings are spray lubricated. An oil

return line connected from the compressor drain outlet

to the vehicle engine crankcase allows for oil return. On

ﬂ ange mounted models the oil drains back directly to the

engine through the mounting ﬂ ange.

COOLING

Air ﬂ owing through the engine compartment from the

action of the engine’s fan and the movement of the vehicle

assists in cooling the compressor. Coolant ﬂ owing from

the engine’s cooling system through connecting lines

enters the head and passes through internal passages

in the cylinder head and is returned to the engine.

Proper cooling is important in maintaining discharge air

temperatures below the maximum recommended 400

degrees Fahrenheit.

Figure 8 illustrates the various approved coolant ﬂ ow

connections. See the tabulated technical data in the back

of this manual for speciﬁ c requirements.

AIR INDUCTION

There are three methods of providing clean air to the Tu-

Flo® 550 compressor:

1. Naturally aspirated Local Air Strainer - Compressor

utilizes its own attached air strainer (polyurethane

sponge or pleated paper dry element).

COMPRESSOR TURBOCHARGING

PARAMETERS

Air entering the compressor inlet during the loaded cycle

must not exceed 250 degrees Fahrenheit (121 degrees

Celsius). A metal inlet line is suggested to help meet this

parameter.

The following compressor crankshaft rotative speed and

inlet pressure relationships may not be exceeded.

Crankshaft Maximum Compressor

R.P.M. Inlet Pressure

2200 RPM 30.0 psi (207 kPa)

2600 RPM 25.0 psi (172.5 kPa)

POLYURETHANE SPONGE STRAINER

Every month, 150 operating hours or 5,000 miles,

whichever occurs ﬁ rst, remove and wash all of the parts.

The strainer element should be cleaned or replaced. If the

element is cleaned, it should be washed in a commercial

solvent or a detergent and water solution. The element

should be saturated in clean engine oil, then squeezed

dry before replacing it in the strainer. Be sure to replace

the air strainer gasket if the entire strainer is removed from

the compressor intake.

PAPER AIR STRAINER DRY ELEMENT-PLEATED

POLYURETHANE SPONGE STRAINER

FIGURE 10 - STRAINERS

PREVENTIVE MAINTENANCE

Regularly scheduled maintenance is the single most

important factor in maintaining the air brake charging

system. Refer to Table A in the Troubleshooting section

for a guide to various considerations that must be given

to the maintenance of the compressor and other related

charging system components.

Important Note: Review the warranty policy before

performing any intrusive maintenance procedures. An

extended warranty may be voided if intrusive maintenance

is performed during this period.

AIR INDUCTION

One of the single most important aspects of compressor

preventive maintenance is the induction of clean air.

The type and interval of maintenance required will vary

depending upon the air induction system used.

The intervals listed under the headings below pertain

to typical highway and street operation. More frequent

maintenance will be required for operation in dusty or

dirty environments.

DRY ELEMENT - PLEATED PAPER STRAINER

Every two months, 800 operating hours or 20,000 miles

whichever occurs ﬁ rst, loosen the spring clip from the

unhinged side of the mounting bafﬂ e and open the cover.

Replace the pleated paper ﬁ lter and secure the cleaned

cover, making sure the ﬁ lter is in position. Be sure to replace

the air strainer gasket if the entire air strainer is removed

from the compressor intake.

270024002100180015001200900600

Compressor Speed (RPM)

Turbo Limits

FIGURE 9 - TURBO LIMITS CURVE

Inlet Pressure (PSIG)

INTAKE ADAPTER

When the engine air cleaner is replaced: Some

compressors are ﬁ tted with compressor intake adapters,

which allow the compressor intake to be connected to the

engine air induction system. In this case, the compressor

receives a supply of clean air from the engine air cleaner.

When the engine air ﬁ lter is changed, the compressor

intake adapter should be checked. If it is loose, remove the

intake adapter, clean the strainer plate, if applicable, and

replace the intake adapter gasket, and reinstall the adapter

securely. Check line connections both at the compressor

intake adapter and at the engine. Inspect the connecting

line for ruptures and replace it if necessary.

COMPRESSOR COOLING

Every 6 months, 1800 operating hours or after each

50,000 miles whichever occurs first, inspect the

compressor discharge port, inlet cavity and discharge line

for evidence of restrictions and carboning. If excessive

buildup is noted, thoroughly clean or replace the affected

parts and closely inspect the compressor cooling system.

Check all compressor coolant lines for kinks and restrictions

to ﬂ ow. Minimum coolant line size is 3/8" I.D. Check coolant

lines for internal clogging from rust scale. If coolant lines

appear suspicious, check the coolant ﬂ ow and compare

to the tabulated technical data present in the back of this

manual. Carefully inspect the air induction system for

restrictions.

LUBRICATION

Every six months, 1800 operating hours or 50,000 miles

whichever occurs ﬁ rst, check external oil supply and

return lines, if applicable, for kinks, bends, or restrictions

to ﬂ ow. Supply lines must be a minimum of 3/16" I.D. and

return lines must be a minimum of 1/2" I.D. Oil return lines

should slope as sharply as possible back to the engine

crankcase and should have as few ﬁ ttings and bends as

possible. Refer to the tabulated technical data in the back

of this manual for oil pressure minimum values.

Check the exterior of the compressor for the presence of

oil seepage and refer to the TROUBLESHOOTING section

for appropriate tests and corrective action.

OIL PASSING

All reciprocating compressors currently manufactured will

pass a minimal amount of oil. Air dryers will remove the

majority of oil prior to entrance into the air brake system. For

particularly oil sensitive systems the Bendix® PuraGuard®

QC™ oil coalescing ﬁ lter can be used in conjunction with

a Bendix air dryer.

If compressor oil passing is suspected, refer to the

TROUBLESHOOTING section and TABLE A for the

symptoms and corrective action to be taken. In addition,

Bendix has developed the "Bendix Air System Inspection

Cup" or BASIC test to help substantiate suspected

excessive oil passing. The steps to be followed when using

the BASIC test are presented in APPENDIX A at the end

of the TROUBLESHOOTING section.

COMPRESSOR DRIVE

Every six months, 1800 operating hours or 50,000

miles, whichever occurs ﬁ rst, check for noisy compressor

operation, which could indicate a worn drive gear coupling,

a loose pulley or excessive internal wear. Adjust and/or

replace as necessary.

If the compressor is belt driven, check for proper belt and

pulley alignment and belt tension. Check all compressor

mounting bolts and retighten evenly if necessary. Check

for leakage and proper unloader mechanism operation.

Repair or replace parts as necessary.

Every 24 months, 7200 operating hours, or after

each 200,000 miles, perform a thorough inspection, and

depending upon the results of this inspection or experience,

disassemble the compressor, clean and inspect all parts

thoroughly, replace all worn or damaged parts using only

genuine Bendix replacements or replace the compressor

with a genuine Bendix remanufactured unit.

GENERAL SERVICE CHECKS

OPERATING TESTS

IN SERVICE OPERATING TESTS

Compressor Performance: Build-up Test

This test is performed with the vehicle parked and the

engine operating at maximum recommended governed

speed. Fully charge the air system to governor cut out (air

dryer purges). Pump the service brake pedal to lower the

system air pressure below 80 psi using the dash gauges.

As the air pressure builds back up, measure the time

from when the dash gauge passes 85 psi to the time it

passes 100 psi. The time should not exceed 40 seconds.

If the vehicle exceeds 40 seconds, test for (and ﬁ x) any

air leaks, and then re- test the compressor performance.

If the vehicle does not pass the test the second time,

use the Advanced Troubleshooting Guide for Air Brake

Compressors, starting on page A-1 of this document to

assist your investigation of the cause(s).

Note: All new vehicles are certiﬁ ed using the FMVSS

121 test (paragraph S5.1.1) by the vehicle manufacturer,

however the above test is a useful guide for in-service

vehicles.

Optional Comparative Performance Check

It may be useful to also conduct the above test with the

engine running at high idle (instead of maximum governed

speed), and record the time taken to raise the system

pressure a selected range (for example, from 90 to 120

psi, or from 100 to 120 psi, etc.) and record it in the

vehicle’s maintenance ﬁ les. Subsequent build-up times

throughout the vehicle’s service life can then be compared

to the ﬁ rst one recorded. (Note: the 40 second guide in

the test above does not apply to this build-up time.) If the

performance degrades signiﬁ cantly over time, you may

use the Advanced Troubleshooting Guide for Air Brake

Compressors, starting on page A-1 of this document, to

assist investigation of the cause(s).

Note: When comparing build-up times, be sure to make

an allowance for any air system modiﬁ cations which would

cause longer times, such as adding air components or

reservoirs. Always check for air system leakage.

AIR LEAKAGE TESTS

Compressor leakage tests need not be performed on a

regular basis. These tests should be performed when; it

is suspected that discharge valve leakage is substantially

affecting compressor build-up performance, or when it is

suspected that the compressor is “cycling” between the load

and unloaded modes due to unloader piston leakage.

These tests must be performed with the vehicle parked

on a level surface, the engine not running, the entire air

system completely drained to 0 P.S.I., and the inlet check

valve detail parts removed, if applicable.

UNLOADER PISTON LEAKAGE

The unloader pistons can be checked for leakage as follows:

with the cylinder head removed from the compressor and

the inlet ﬂ ange securely covered, apply 120 psi of air

pressure to the governor port. Listen for an escape of air

at the inlet valve area. An audible escape of air should not

be detected.

DISCHARGE VALVE LEAKAGE

Unloader piston leakage must be repaired before this test

is performed. Leakage past the discharge valves can be

detected as follows: Remove the discharge line and apply

shop air back through the discharge port. Listen for an

escape of air at the compressor inlet cavity. A barely audible

escape of air is generally acceptable.

If the compressor does not function as described above

or if the leakage is excessive, it is recommended that it be

returned to the nearest authorized Bendix distributor for a

factory remanufactured compressor. If it is not possible,

the compressor can be repaired using a genuine Bendix

cylinder head maintenance kit. Retest the cylinder head

after installation of the kit.

REMOVAL AND DISASSEMBLY

GENERAL

The following disassembly and assembly procedure is

presented for reference purposes and presupposes that

a major rebuild of the compressor is being undertaken.

Several maintenance kits are available which do not require

full disassembly. The instructions provided with these

parts and kits should be followed in lieu of the instructions

presented here.

REMOVAL

These instructions are general and are intended to be

a guide, in some cases additional preparations and

precautions are necessary.

1. Block the wheels of the vehicle and drain the air

pressure from all the reservoirs in the system.

2. Drain the engine cooling system and the cylinder head

of the compressor. Identify and disconnect all air, water

and oil lines leading to the compressor.

3. Remove the governor and any supporting bracketry

attached to the compressor and note their positions

on the compressor to aid in reassembly.

4. Remove the discharge and inlet ﬁ ttings, if applicable,

and note their position on the compressor to aid in

reassembly.

5. Remove the ﬂ ange or base mounting bolts and remove

the compressor from the vehicle.

6. Remove the drive gear(s) or pulley from the compressor

crankshaft using a gear puller. Inspect the pulley or gear

and associated parts for visible wear or damage. Since

these parts are precision ﬁ tted, they must be replaced

if they are worn or damaged.

PREPARATION FOR DISASSEMBLY

Remove road dirt and grease from the exterior of the

compressor with a cleaning solvent. Before the compressor

is disassembled, the following items should be marked to

show their relationship when the compressor is assembled.

Mark the rear end cover in relation to the crankcase.

Mark the base plate or base adapter in relation to the

crankcase.

A convenient method to indicate the above relationships

is to use a metal scribe to mark the parts with numbers or

lines. Do not use marking methods such as chalk that can

be wiped off or obliterated during rebuilding.

CYLINDER HEAD

Remove the six cylinder head cap screws (1) and tap the

head with a soft mallet to break the gasket seal. Remove

the unloader cover plate cap screws (2), lockwashers (3)

and the unloader cover plate (4). Scrape off any gasket

material (5) from the cover plate, cylinder head and

crankcase.

1. Remove the unloader pistons (7), o-rings (6) and

springs (8).

2. Inspect the unloader piston bushings (9) for nicks,

wear, corrosion and scoring. It is recommended that

the compressor be replaced if it is determined that the

unloader bushing is damaged or worn excessively.

Before disassembling the discharge valve mechanism,

measure and record the discharge valve travel (from closed

to completely open).

3. If the measured discharge valve travel exceeds .046

inches, the compressor should be replaced. If the

discharge valve travel does not exceed .046, using a

9/16" Allen wrench, remove the discharge valve seats

(18), valves (17) and valve springs (16).

4. Remove the inlet valve stops (14), valves (17), valve

seats (11), valve springs (12) and gaskets (10). It is

recommended that a tool such as a J-25447-B, produced

by Kent Moore Tool Division Roseville, Michigan phone

1-800-328-6657, be used to remove the inlet valve

stop.

CRANKCASE BOTTOM COVER OR ADAPTER

DISASSEMBLY

1. Remove the cap screws (22) securing the bottom cover

or adapter (21). Tap with a soft mallet to break the

gasket seal. Scrape off any gasket material (20) from

the crankcase and bottom cover or adapter.

CONNECTING ROD DISASSEMBLY

Before removing the connecting rod, mark the connecting

rods (37) and their caps (39) to ensure correct reassembly.

The connecting rod and cap are a matched set therefore

the caps must not be switched or rotated end for end.

1. Remove the connecting rod bolts (40) and bearing caps

(39).

2. Push the pistons (26) with the connecting rods

(37) attached out the top of the cylinder bore of the

crankcase. Replace the bearing caps on the connecting

rods.

3. Remove the piston rings (23-25) from the piston. If

the piston is to be removed from the connecting rod,

remove the wrist pin Teﬂ on plugs (28) and press the

wrist pin (27) from the piston and connecting rod.

4. If the piston is removed from the rod, inspect the wrist

pin bore in the piston and bronze wrist pin bushing

(36) in the connecting rod. If excessive wear is noted

or suspected, replace the connecting rod and piston.

COMPRESSOR CRANKCASE DISASSEMBLY

1. Remove the key or keys (30) from the crankshaft (29)

and any burrs from the crankshaft where the key or keys

were removed. (Note: Through drive compressors may

have a crankshaft key at both ends.)

2. Remove the four cap screws (35) and lockwashers or

nuts and lockwashers that secure the rear end cover

(34) to the crankcase.

3. Remove the rear end cover (34), thrust washer (31) and

end cover oil seal ring (33), taking care not to damage

the bearing if present in the end cover.

4. If the compressor has ball type main bearings, press the

crankshaft (29) and ball bearings from the crankcase,

then press the ball bearings from the crankshaft.

5. Press the oil seal out of the compressor crankcase, if

so equipped.

CLEANING OF PARTS

GENERAL

All parts should be cleaned in a good commercial grade of

solvent and dried prior to inspection.

CYLINDER HEAD

Remove carbon deposits from the discharge cavity and

rust and scale from the cooling cavities of the cylinder head

body. Scrape all foreign matter from the body surfaces and

use shop air pressure to blow the dirt particles from the

cavities. Clean carbon and dirt from the inlet and unloader

passages. Use shop air to blow the carbon and dirt deposits

from the unloader passages.

OIL PASSAGES

Thoroughly clean all oil passages through the crankshaft,

crankcase, end covers, base plate or base adapter. Inspect

the passages with a wire to be sure. Blow the loosened

foreign matter out with air pressure.

INSPECTION OF PARTS

CYLINDER HEAD BODY

Inspect the cylinder head for cracks or damage. With the

cylinder head and head gasket secured to a ﬂ at surface or

crankcase, apply shop air pressure to one of the coolant

ports with all others plugged, and check for leakage by

applying a soap solution to the exterior of the body. If

leakage is detected, replace the compressor.

ITEM QTY DESCRIPTION ITEM QTY DESCRIPTION ITEM QTY DESCRIPTION

1 6 Cylinder Head Cap Screws 16 2 Discharge Valve Spring 31 2 Thrust Washer

2 4 Unloader Plate Cap Screws 17 2 Discharge Valve 32 2 Sleeve (or Ball) Bearing

3 4 Unloader Plate Lock Washers 18 2 Discharge Valve Stop 33 1 End Cover Seal

4 1 Unloader Plate 19 1 Cylinder Head Gasket 34 1 End Cover

5 1 Unloader Plate Gasket 20 1 Base Gasket 35 4 End Cover Cap Screws

6 2 O-ring 21 1 Base Plate 36 2 Wrist Pin Bushing

7 2 Unloader 22 6 Base Plate Cap Screws 37 2 Connecting Rod

8 2 Spring 23 6 Standard Piston Rings 38 2 Conn. Rod Inserts (Sets)

9 2 Unloader Bushing 24 8 Oil Ring 39 2 Connecting Rod Caps

10 2 Gasket 25 4 Expander Ring 40 4 Connecting Rod Bolts

11 2 Inlet Valve Seat 26 2 Piston 41 1 Ball Bearing

12 2 Inlet Valve 27 2 Wrist Pin 42 1 Retaining Ring

13 2 Inlet Valve Spring 28 4 Wrist Pin Button 43 1 Seal

14 2 Inlet Valve Stop 29 1 Crankshaft 44 1 Cotter Pin

15 2 Discharge Valve Stop 30 1 Crankshaft Key 45 1 Locknut

BALL BEARING

(MACK EXTENDED

FLANGE)

NAMEPLATE

24 28

3839

CYLINDER

HEAD

CRANKCASE

FLANGE

MOUNT

BASE

MOUNT

CRANKCASE

30 34

END COVERS

Check for cracks and external damage. If the crankshaft

main bearing (32) is installed in the end cover (34),

check for excessive wear and ﬂ at spots and replace if

necessary.

CRANKCASE

Check all crankcase surfaces for cracks and damage. On

compressors where ball bearing main bearings are used

the difference between the O.D. of the outer race and the

I.D. of the crankcase hole should be .0003 in. tight to .0023

in. loose. This is to maintain the correct ﬁ t. The compressor

must be replaced if the ﬁ t is too loose.

On compressors ﬁ tted with precision, sleeve main bearings,

the difference between the O.D. of the crankshaft journal

and the main bearing l.D. must not exceed .005 in. If the

clearance is greater than .005 in. the bearing must be

replaced.

The cylinder bores should be checked with inside

micrometers or calipers. Cylinder bores which are scored

or out of round by more than .0005 in. or tapered more than

.0005 in. should be re-bored or honed oversize. Oversized

pistons and piston rings are available in .010 in., .020 in.

and .030 in. oversizes. Cylinder bores must be smooth,

straight and round. Clearance between the cast iron pistons

and cylinder bores should be between .002 in. minimum

and .004 in. maximum.

PISTON RINGS

Check the pistons for scores, cracks or enlarged ring

grooves; replace the pistons if any of these conditions are

found. Measure each piston with a micrometer in relation

to the cylinder bore diameter to be sure the diametrical

clearance is between .002 in. minimum and .004 in.

maximum.

Check the ﬁ t of the wrist pins to the pistons and connecting

rod bushings. The wrist pin should be a light press ﬁ t in

the piston. If the wrist pin is a loose ﬁ t, the piston and pin

assembly should be replaced. Check the ﬁ t of the wrist

pin in the connecting rod bushing by rocking the piston.

This clearance should not exceed .0007 in. Replace the

connecting rod and cap assembly which includes the wrist

pin bushings if excessive clearance is found. Check the ﬁ t

of the rings in the piston ring grooves. Check the ring gap

with the rings installed in the cylinder bores. Refer to Figure

12 for correct gap and groove clearances.

CRANKSHAFT

Check the crankshaft threads, keyways, tapered ends

and all machined and ground surfaces for wear, scores,

or damage. Standard crankshaft journals are 1.1242 in.

- 1.1250 in. in diameter. If the crankshaft journals are

excessively scored or worn or out of round and cannot be

reground, the compressor must be replaced. Connecting

rod bearing inserts are available in .010 in., .020 in.

and .030 in. undersizes for compressors with reground

crankshafts. Main bearing journals must be maintained

so the ball bearings are a snug ﬁ t or so that no more than

.005 in. clearance exists between the precision sleeve main

bearing and the main bearing journals on the crankshaft.

Check to be sure the oil passages are open through the

crankshaft.

CONNECTING ROD BEARINGS

Used bearing inserts must be replaced. The connecting rod

and cap are a matched set and therefore the caps must not

be switched or rotated end for end. The solid inserts must

be installed in the rod and the slotted inserts into the cap.

Make sure the locating tangs on the inserts engage with

the locating notches in the rod and cap. Clearance between

the connecting rod journal and the connecting rod bearing

must not be less than .0003 in. or more than .0021 in. after

rebuilding.

REPAIRS

UNLOADER

A new cylinder head maintenance kit should be used when

rebuilding. Note: The entire contents of this kit must

be used. Failure to do so may result in compressor

failure. The unloader pistons in the kit are prelubricated

SIDE CLEARANCE

.000

.006

STANDARD PISTON

RING

.002

.004 OIL RING

EXPANDER

RING

END GAP

.002

.013

.010

.040

Segment

Ring End

Gap

FIGURE 12 - RING CONFIGURATION

Compression

the slot toward the ﬂ ange. Insert the crankshaft and the

rear thrust washer with the tang toward the rear of the

compressor.

Place the oil seal ring on the boss of the rear end cover and

install the end cover making sure not to pinch the seal ring.

Ensure the tang of the thrust washer is inserted in the slot

of the end cover. Fasten the end cover to the crankcase

with the four cover cap screws. Torque the cap screws to

175-225 inch pounds in a cross pattern.

with a special lubricant piece number 239379 and need

no additional lubrication. Install the springs and unloader

pistons in their bores being careful not to cut the o-rings.

Install the unloader cover gasket and unloader cover and

secure the cover cap screws. Tighten the cap screws to

175-225 in. lbs. in a crossing pattern after ﬁ rst snugging

all screws.

DISCHARGE VALVES, VALVE STOPS AND

SEATS

If the discharge valve seats merely show signs of slight

wear, they can be dressed by using a lapping stone,

grinding compound and grinding tool, however, it is

recommended that a cylinder head maintenance kit be

used. Install new discharge valve springs and valves.

Screw in the discharge valve seats, and tighten to 70-90

ft.-lbs. Discharge valve travel should be between .030 in. to

.046 in. To test for leakage by the discharge valves, apply

100 psi to the cylinder head discharge port and apply a

soap solution to the discharge valve and seats. Leakage

in the form of soap bubbles is permissible. If excessive

leakage is found, leave the air pressure applied and with

the use of a ﬁ ber or hardwood dowel and a hammer, tap

the discharge valves off their seats several times. This will

help the valves to seat and should reduce the leakage.

With the air pressure still applied at the discharge port of

the cylinder head, check for leakage around the discharge

valve stop on the top of the cylinder head casting. No

leakage is permitted.

INLET VALVES AND SEATS

Inlet valves and springs should be replaced. However, if

the inlet valve seats show signs of slight nicks or scratches,

they can be redressed with a ﬁ ne piece of emery cloth or

by lapping with a lapping stone, grinding compound and

grinding tool. If the seats are damaged to the extent that

they cannot be reclaimed, they must be replaced.

ASSEMBLY

General Note: All torques speciﬁ ed in this manual are

assembly torques and typically can be expected to fall off

after assembly is accomplished. Do not retorque after

initial assembly torques fall unless instructed otherwise.

A compiled listing of torque speciﬁ cations is presented on

page 13 of this manual.

To convert inch pounds of torque to foot pounds of torque,

divide inch pounds by 12.

inch pounds ÷ 12 = foot pounds

To convert foot pounds of torque to inch pounds of torque,

multiply foot pounds by 12.

foot pounds x 12 = inch pounds

INSTALLING CRANKSHAFT

Press new sleeve bearings in the end cover and crankcase.

Ensure that the slot in the bearings line up with the oil

passages in the end cover or crankcase. If you have a

model with no oil passage present in the crankcase, press

the sleeve bearing into the crankcase with the slot located

90 degrees from vertical.

Install the front thrust washer with the tang inserted in

FIGURE 13 - PISTON COMPARISON

2.78

2.17

1.06

1.25

OTHER BENDIX®

TU-FLO® AIR COMPRESSORS

TU-FLO® 550

AIR COMPRESSOR

PISTON COMPARISON

FIGURE 14 - PISTON & RINGS

COMPRESSION RING (23)

SEGMENT RING (24)

SPACER RING (25)

SEGMENT RING

(24)

journal bearing segments (38) on the connecting rod (37)

and connecting rod cap (39). Tighten the connecting rod

bolts (40) evenly and torque to 150 - 170 inch pounds.

Install the other connecting rod and piston in the same

manner. It is recommended that new connecting rod cap

screws be used.

Before replacing the cylinder head on the crankcase

ensure the correct pistons have been used by turning the

crankshaft one complete revolution such that each piston

moves to its maximum upward stroke. At the maximum

upward stroke position each piston should move to the top

of the crankcase. If the piston does not approach the top

of the crankcase the piston is incorrect and if not replaced

could result in compressor damage.

BASE PLATE OR BASE ADAPTER

Position the base plate or base adapter gasket (20) on the

crankcase and install the base plate or base adapter (21)

as marked before disassembly. Tighten the six cap screws

(22), securing the cast iron base adapter evenly to a torque

of 175-225 inch pounds for base plate or cover in a crossing

pattern after ﬁ rst snugging all 6 screws.

CYLINDER HEAD

Place the cylinder head gasket (19) and cylinder head

on the compressor crankcase and install the six cylinder

head cap screws. Snug the cylinder head cap screws prior

to torquing the cap screws to 300-360 in. lbs. in a cross

pattern. Retorque the unloader cover cap screws to 170-

225 in. Ibs.

FINAL COMPRESSOR ASSEMBLY

Install all crankshaft keys making certain to support the

crankshaft to avoid bearing damage. Install the crankshaft

nut where applicable. When installing drive couplings or

gears, do not exceed 120 foot pounds torque on the

crankshaft nut.

Use covers, plugs, or masking tape to protect all ports if

compressor is not to be installed immediately. Protect the

ends of the crankshaft against damage by wrapping with

masking tape or friction tape.

TESTING REBUILT COMPRESSOR

In order to properly test a compressor under operating

conditions, a test rack for correct mounting, cooling,

lubricating, and driving the compressor is necessary. Such

tests are not compulsory if the unit has been carefully

rebuilt by an experienced person. A compressor efﬁ ciency

or build up test can be run which is not too difﬁ cult. An

engine lubricated compressor must be connected to an oil

supply line of at least 15 P.S.I. pressure during the test and

an oil return line must be installed to keep the crankcase

drained.

PISTONS AND CONNECTING RODS

If the pistons are to be replaced ensure that the correct

pistons are being installed. Note that the pistons for the

Tu-Flo® 550 compressor are similar to those of other Bendix

compressor models but may be identiﬁ ed by the piston

diameter and the distance to the center of the wrist pin from

the top of the piston as shown in Figure 13.

PISTON RINGS

Check each ring end gap in a cylinder bore before

installation. Place the ring in the top of the cylinder bore

and using the piston, push the ring to the midpoint of the

cylinder bore and check the ring gap. If the end gaps are

incorrect either the wrong repair size has been purchased

or the compressor is worn beyond speciﬁ cation and should

be replaced.

Install the rings on the pistons per the following instructions

starting at the center of the piston and moving outward.

1. Install the spacer and segment rings as follows. Place

the spacer ring (25) in the piston groove, the ends of

the spacer must butt and not overlap. Install the top

segment (24) by inserting one end above the spacer

in the ring groove, 120 degrees from the spacer ends

and wind the segment into position. Install the bottom

segment in the same manner beneath the spacer

making sure the gap is staggered 120 degrees from

both the top ring segment and the spacer end gaps.

Before using be sure both painted ends of the spacer

are visible and butted.

2. Install the compression rings (23) in the proper grooves

with the bevel or “pip” mark (if any) toward the top of

the piston. (Refer to Figure 14.)

Check the ring side clearance of each ring in the piston ring

groove. (Refer to Figure 14.) If the side clearance is too

large, the piston ring groove is worn beyond speciﬁ cations

and the piston must be replaced.

Rotate the piston rings in their respective groove so that

each end gap is at least 90 degrees from the previous

ring’s end gap.

Lubricate the wrist pin (22) and wrist pin bushing in the

connecting rod with engine oil. Assemble the upper portion

of the connecting rods and the pistons with the wrist pins.

Insert the wrist pin buttons (28) in the ends of the wrist pin.

Lubricate the pistons and rings with engine oil. Using a ring

compression tool return the piston to the cylinder bore.

Turn the crankshaft so that one of its connecting rod journals

is in the downward, center position. Install the crankshaft

Connect to the compressor discharge port, a reservoir with

a volume of 1500 cubic inches, including the volume of the

connecting line. With the compressor operating at 2100

R.P.M., the time required to raise the reservoir(s) pressure

from 85 psi to 100 psi should not exceed 7 seconds. During

this test, the compressor should be checked for gasket

leakage and noisy operation, as well as unloader operation

and leakage.

If the compressor functions as indicated reinstall on the

vehicle connecting all lines as marked in the disassembly

procedure.

TU-FLO® 550 AIR COMPRESSOR

SPECIFICATIONS

Average weight ........................................................... 53

Number of cylinders ...................................................... 2

Bore size ............................................................. 2.78 In.

Stroke ................................................................. 1.50 In.

Displacement at 1250 RPM ............................ 13.2 CFM

Maximum recommended RPM ...................... 3000 RPM

Minimum coolant ﬂ ow (water cooled) at

Maximum RPM .............................................. 2.5 GPM

Minimum RPM ................................................. .5 GPM

Approximate horsepower required at

1250 RPM at 120 PSIG (naturally aspirated) ............ 2.5

Turbocharge limits

See Compressor Turbocharging Parameters

Maximum inlet air temperature .............................. 250°F

Maximum discharge air temperature ..................... 400°F

Minimum pressure required to unload

(naturally aspirated) ........................................... 60 PSIG

Minimum oil pressure required at

engine idling speed ............................................ 15 PSIG

Minimum oil pressure required at

maximum governed engine speed .................... 15 PSIG

Minimum discharge-line size ............................. 1/2" I.D.

Minimum coolant-line size ................................. 3/8" I.D.

Minimum oil-supply line size ............................ 3/16" I.D.

Minimum oil-return line size ............................... 1/2" I.D.

Minimum air-inlet line size .................................. 5/8” I.D.

Minimum unloader-line size ............................. 3/16" I.D.

TORQUE SPECIFICATIONS

Bolt, Nut or Screw ........................... Assembly Torque

(in. lbs.)

Cylinder Head ..................................................440 - 500

Unloader Cover Plate ...................................... 175 - 225

Discharge Valve Seat ............. 840 - 1080 (70-90 ft. lbs.)

Inlet Valve Stop ....................... 840 - 1080 (70-90 ft. lbs.)

End Cover ........................................................ 175 - 225

Connecting Rod ............................................... 150 - 170

Bottom Cover ................................................... 175 - 225

Air Strainer ....................................................... 125 - 150

Inlet Fitting ....................................................... 175 - 225

Discharge Fitting .............................................. 175 - 225

Governor or Governor Adapter ........................ 175 - 225

Pipe Plugs

1/16 .................................................................. 35 - 50

1/8 .................................................................. 85 - 105

1/4 ................................................................ 130 - 170

3/8 ................................................................ 160 - 200

1/2 ................................................................ 200 - 270

Pipe Bushing

1/2 ................................................................ 175 - 225

Crankshaft Nut:

Marsden or Castle ........... 1200-1440 (100-120 ft. lbs.)

P/N 298125 (Metric Thread) ......2640-3048 (220-254 ft.

lbs.)

DIMENSIONAL DATA

Port Sizes

Water inlet ............................................... 1/2 - 14 NPT

Water outlet ............................................. 1/2 - 14 NPT

Air discharge ........................................... 1/2 - 14 NPT

Governor ................................................. 1/8 - 27 NPT

Oil inlet (end cover) ................................. 1/8 - 27 NPT

Oil return: Base mount ........................... 1/2 - 14 NPT

Piston

(standard) .................................................. 2.77825 in.

(.010 oversize) .......................................... 2.78825 in.

(.020 oversize) .......................................... 2.79825 in.

(.030 oversize) .......................................... 2.80825 in.

Cylinder bore

(standard) .................................................... 2.7810 in.

(.010 oversize) ............................................ 2.7910 in.

(.020 oversize) ............................................ 2.8010 in.

(.030 oversize) ............................................. 2.8110 in.

MAINTENANCE KITS AND AVAILABLE SERVICE

PARTS

Cylinder Maintenance Kit

Piston Ring Kit (standard and oversizes)

Piston and Rod Kit (standard and oversizes)

Crankshaft Bearing Kit

Gasket & Seal Kit

COMPRESSOR TROUBLESHOOTING

IMPORTANT: The troubleshooting contained in this section

considers the compressor as an integrated component of

the overall air brake charging system and assumes that

an air dryer is in use. The troubleshooting presented will

cover not only the compressor itself, but also other charging

system devices as they relate to the compressor.

WARNING! PLEASE READ AND FOLLOW

THESE INSTRUCTIONS TO AVOID PERSONAL

INJURY OR DEATH:

When working on or around a vehicle, the following

general precautions should be observed at all times.

1. Park the vehicle on a level surface, apply the parking

brakes, and always block the wheels. Always wear

safety glasses.

2. Stop the engine and remove ignition key when

working under or around the vehicle. When working

in the engine compartment, the engine should be

shut off and the ignition key should be removed.

Where circumstances require that the engine be

in operation, EXTREME CAUTION should be used

to prevent personal injury resulting from contact

with moving, rotating, leaking, heated or electrically

charged components.

3. Do not attempt to install, remove, disassemble

or assemble a component until you have read

and thoroughly understand the recommended

procedures. Use only the proper tools and observe

all precautions pertaining to use of those tools.

4. If the work is being performed on the vehicle’s

air brake system, or any auxiliary pressurized air

systems, make certain to drain the air pressure

from all reservoirs before beginning ANY work

on the vehicle. If the vehicle is equipped with an

AD-IS® air dryer system or a dryer reservoir module,

be sure to drain the purge reservoir.

5. Following the vehicle manufacturer’s recommended

procedures, deactivate the electrical system in a

manner that safely removes all electrical power

from the vehicle.

6. Never exceed manufacturer’s recommended

pressures.

7. Never connect or disconnect a hose or line

containing pressure; it may whip. Never remove

a component or plug unless you are certain all

system pressure has been depleted.

8. Use only genuine Bendix® replacement parts,

components and kits. Replacement hardware,

tubing, hose, ﬁ ttings, etc. must be of equivalent

size, type and strength as original equipment and

be designed speciﬁ cally for such applications and

systems.

9. Components with stripped threads or damaged

parts should be replaced rather than repaired. Do

not attempt repairs requiring machining or welding

unless speciﬁ cally stated and approved by the

vehicle and component manufacturer.

10. Prior to returning the vehicle to service, make

certain all components and systems are restored

to their proper operating condition.

11. For vehicles with Antilock Traction Control (ATC),

the ATC function must be disabled (ATC indicator

lamp should be ON) prior to performing any vehicle

maintenance where one or more wheels on a drive

axle are lifted off the ground and moving.

A-1

Appendix A

Advanced Troubleshooting Guide for Air Brake Compressors

Air brake charging system:

Slow build (9.0) .....................................A-9-10

Doesn’t build air (10.0) ............................. A-11

Air dryer:

Doesn’t purge (14.0) ................................ A-12

Safety valve releases air (12.0) ............... A-12

Compressor:

Constantly cycles (15.0) .......................... A-12

Leaks air (16.0) ........................................ A-13

Safety valve releases air (11.0) ............... A-11

Noisy (18.0) ............................................A-13

Reservoir:

Safety valve releases air (13.0) ............... A-12

INDEX

Air Coolant

Engine

Oil

Compressor leaks coolant (17.0)....................A-13

Oil consumption (6.0) ......................................A-9

Oil Test Card results (1.0) .................................A-4

Oil is present:

On the outside of the compressor (2.0) ......A-5

At the air dryer purge/exhaust

or surrounding area (3.0) ........................A-5

In the supply reservoir (4.0) .................... A-6-8

At the valves (5.0) .......................................A-8

At air dryer cartridge (7.0) ...........................A-9

In the ping tank or compressor

discharge aftercooler (8.0) ......................A-9

Symptom Page Number

(1) Oil Leakage at Head Gasket .....A-14

(2) System Leakage .......................A-14

(3) Compressor Discharge and

Air Dryer Inlet Temperature ...........A-15

(4) Governor Malfunction ................A-14

(5) Governor Control Line ...............A-15

(6) Compressor Unloader ...............A-15

BASIC™ Test Information ........ A-16-18

Test Procedures

Maintenance Schedule and

Usage Guidelines (Table A) ..... A-3

Symptom Page Number

Maintenance & Usage Guidelines

The guide consists of an introduction to air brake charging system components, a table

showing recommended vehicle maintenance schedules, and a troubleshooting symptom

and remedy section with tests to diagnose most charging system problems.

A-2

Introduction to the Air Brake Charging System

builds the air pressure for the air brake system. The air

compressor is typically cooled by the engine coolant system

and lubricated by the engine oil supply.

The compressor's unloader mechanism and governor

(along with a synchro valve for the Bendix® DuraFlo™ 596

air compressor) control the brake system air pressure

between a preset maximum and minimum pressure level

by monitoring the pressure in the service (or “supply”)

reservoir. When the air pressure becomes greater than that

of the preset “cut-out”, the governor controls the unloader

mechanism of the compressor to stop the compressor from

building air and also causes the air dryer to purge. As the

service reservoir air pressure drops to the “cut-in” setting

of the governor, the governor returns the compressor back

to building air and the air dryer to air drying mode.

As the atmospheric air is compressed, all the water vapor

originally in the air is carried along into the air system, as

well as a small amount of the lubricating oil as vapor.

The duty cycle is the ratio of time the compressor spends

building air to the total engine running time. Air compressors

are designed to build air (run “loaded”) up to 25% of the

time. Higher duty cycles cause conditions that affect air

brake charging system performance which may require

additional maintenance. Factors that add to the duty cycle

are: air suspension, additional air accessories, use of an

undersized compressor, frequent stops, excessive leakage

from ﬁ ttings, connections, lines, chambers or valves, etc.

The discharge line allows the air, water-vapor and

oil-vapor mixture to cool between the compressor and air

dryer. The typical size of a vehicle's discharge line, (see

column 2 of Table A on page A-3) assumes a compressor

with a normal (less than 25%) duty cycle, operating in

a temperate climate. See Bendix and/or other air dryer

manufacturer guidelines as needed.

When the temperature of the compressed air that enters

the air dryer is within the normal range, the air dryer can

remove most of the charging system oil. If the temperature

of the compressed air is above the normal range, oil as

oil-vapor is able to pass through the air dryer and into the

air system. Larger diameter discharge lines and/or longer

discharge line lengths can help reduce the temperature.

The discharge line must maintain a constant slope down

from the compressor to the air dryer inlet ﬁ tting to avoid low

points where ice may form and block the ﬂ ow. If, instead,

ice blockages occur at the air dryer inlet, insulation may

be added here, or if the inlet ﬁ tting is a typical 90 degree

ﬁ tting, it may be changed to a straight or 45 degree ﬁ tting.

For more information on how to help prevent discharge

line freeze-ups, see Bendix Bulletins TCH-08-21 and

TCH-08-22 (see pages A-19-21). Shorter discharge line

lengths or insulation may be required in cold climates.

The air dryer contains a ﬁ lter that collects oil droplets, and

a desiccant bed that removes almost all of the remaining

water vapor. The compressed air is then passed to the air

brake service (supply) reservoir. The oil droplets and the

water collected are automatically purged when the governor

reaches its “cut-out” setting.

For vehicles with accessories that are sensitive to small

amounts of oil, we recommended installation of a Bendix®

PuraGuard® system ﬁ lter, designed to minimize the amount

of oil present.

Air Dryer

Reservoir Drain

Service Reservoir

(Supply Reservoir)

Compressor

Governor

(Governor plus Synchro valve

for the Bendix® DuraFlo™ 596

Compressor)

Discharge

Line Optional “Ping” Tank

Optional Bendix® PuraGuard®

System Filter or PuraGuard QC™

Oil Coalescing Filter

The Air Brake Charging System supplies the

compressed air for the braking system as well as other air

accessories for the vehicle. The system usually consists

of an air compressor, governor, discharge line, air dryer,

and service reservoir.

A-3

Compressor with up to 25% duty cycle

Footnotes:

1. With increased air demand the air dryer cartridge needs to be

replaced more often.

2. Use the drain valves to slowly drain all reservoirs to zero psi.

3. Allow the oil/water mixture to fully settle before measuring oil

quantity.

4. To counter above normal temperatures at the air dryer inlet, (and

resultant oil-vapor passing upstream in the air system) replace the

discharge line with one of a larger diameter and/or longer length.

This helps reduce the air's temperature. If sufﬁ cient cooling occurs,

the oil-vapor condenses and can be removed by the air dryer.

Discharge line upgrades are not covered under warranty. Note:

To help prevent discharge line freeze-ups, shorter discharge line

lengths or insulation may be required in cold climates. (See Bendix

Recom- Recom- Acceptable

Typical Discharge mended mended Reservoir

Compressors Line Air Dryer Reservoir Oil Contents3

No. of Spec'd Cartridge Drain at Regular

Axles Replacement1 Schedule2 Drain Interval

High Air Use

Low Air Use

e.g. Double/triple trailer, open

highway coach/RV, (most)

pick-up & delivery, yard or

terminal jockey, off-highway,

construction, loggers, concrete

mixer, dump truck, ﬁ re truck.

e.g. Line haul single trailer

w/o air suspension, air over

hydraulic brakes.

e.g. Line haul single trailer

with air suspension,

school bus.

less

Table A: Maintenance Schedule and Usage Guidelines

Recom-

mended

Every

Month -

Max of ev-

ery 90 days

Every

Month

Every 3

Years

Every 2

Years

Every

Year

I.D.

Vehicle Used for:

Column 1 Column 2 Column 3 Column 4 Column 5

Regularly scheduled maintenance is the single most important factor in maintaining the air brake charging

Length

6 ft.

1/2 in.

9 ft.1/2 in.

12 ft.

1/2 in.

3/4 in. 12 ft.

BASIC™ test

acceptable

range:

5 oil units

per month.

See

appendix

For oil carry-over

control4 suggested

upgrades:

5/8 in. 15 ft.

For oil carry-over

control4 suggested

upgrades:

5/8 in. 9 ft.

For oil carry-over

control4 suggested

upgrades:

5/8 in. 12 ft.

Compressor with less than 15% duty

cycle

Compressor with up to 25% duty cycle

Bendix® BA-921® air compressor

Bendix® Tu-Flo® 550 air compressor

Bendix® Tu-Flo® 750 air compressor

Bendix® BA-922®, or DuraFlo™ 596 air compressor

BASIC™ test

acceptable

range:

3 oil units

per month.

See

appendix

For the

BASIC™

Test Kit:

Order

Bendix

P/N

5013711

e.g. City transit bus, refuse,

bulk unloaders, low boys,

urban region coach, central

tire inﬂ ation.

(See footnote 7)

Bulletins TCH-08-21 and TCH-08-22, included in Appendix B, for

more information.)

5. For certain vehicles/applications, where turbo-charged inlet air is

used, a smaller size compressor may be permissible.

6. Note: Compressor and/or air dryer upgrades are recommended

in cases where duty cycle is greater than the normal range (for

the examples above).

7. For correct compressor upgrades consult Bendix - Please note

that because a compressor is listed in the same area of the chart

does not necessarily mean that it would be a suitable candidate

for upgrade purposes.

For Bendix® Tu-Flo® 550 and 750 compressors, unloader service is

recommended every 250,000 miles.

A-4

Air Brake Charging System Troubleshooting

1.0 Oil Test Card

Results Not a valid test. Discontinue using this test.

Do not use this card test to diagnose compressor

"oil passing" issues. They are subjective

and error prone. Use only the Bendix® Air

System Inspection Cup (BASIC™) test and the

methods described in this guide for advanced

troubleshooting.

The Bendix® BASIC™ test should be the

deﬁ nitive method for judging excessive

oil fouling/oil passing. (See Appendix A,

on page A-16 for a ﬂ owchart and expanded

explanation of the checklist used when

conducting the BASIC™ test.)

Symptom: What it may indicate: What you should do:

How to use this guide:

Find the symptom(s) that you see, then move to the right

to ﬁ nd the possible causes (“What it may indicate”) and

remedies (“What you should do”).

Review the warranty policy before performing any intrusive

compressor maintenance. Unloader or cylinder head gasket

replacement and resealing of the bottom cover plate are

usually permitted under warranty. Follow all standard safety

procedures when performing any maintenance.

Look for:

Normal - Charging system is working within

normal range.

Check - Charging system needs further

investigation.

Bendix®

BASIC™ Test

WARNING! Please READ and follow these instructions to

avoid personal injury or death:

When working on or around a vehicle, the following general

precautions should be observed at all times.

1. Park the vehicle on a level surface, apply the parking

brakes, and always block the wheels. Always wear safety

glasses.

2. Stop the engine and remove ignition key when working

under or around the vehicle. When working in the engine

compartment, the engine should be shut off and the ignition

key should be removed. Where circumstances require that

the engine be in operation, EXTREME CAUTION should be

used to prevent personal injury resulting from contact with

moving, rotating, leaking, heated or electrically charged

components.

3. Do not attempt to install, remove, disassemble or

assemble a component until you have read and thoroughly

understand the recommended procedures. Use only the

proper tools and observe all precautions pertaining to use

of those tools.

4. If the work is being performed on the vehicle’s air brake

system, or any auxiliary pressurized air systems, make

certain to drain the air pressure from all reservoirs before

beginning ANY work on the vehicle. If the vehicle is

equipped with an AD-IS® air dryer system or a dryer

reservoir module, be sure to drain the purge reservoir.

5. Following the vehicle manufacturer’s recommended

procedures, deactivate the electrical system in a manner

that safely removes all electrical power from the vehicle.

6. Never exceed manufacturer’s recommended pressures.

7. Never connect or disconnect a hose or line containing

pressure; it may whip. Never remove a component or

plug unless you are certain all system pressure has been

depleted.

8. Use only genuine Bendix® replacement parts, components

and kits. Replacement hardware, tubing, hose, ﬁ ttings,

etc. must be of equivalent size, type and strength as

original equipment and be designed speciﬁ cally for such

applications and systems.

9. Components with stripped threads or damaged parts

should be replaced rather than repaired. Do not attempt

repairs requiring machining or welding unless speciﬁ cally

stated and approved by the vehicle and component

manufacturer.

10. Prior to returning the vehicle to service, make certain all

components and systems are restored to their proper

operating condition.

11. For vehicles with Antilock Traction Control (ATC), the ATC

function must be disabled (ATC indicator lamp should be

ON) prior to performing any vehicle maintenance where

one or more wheels on a drive axle are lifted off the ground

and moving.





A-5

(a)



Symptom: What it may indicate: What you should do:

2.2 Oil leaking

from compressor: (a) Excessive leak at head gasket.

(b) Leak at bottom cover plate.

gasket.

(d) Leak through crankcase.

(e) (If unable to tell source of leak.)

 Go to Test 1 on page A-14.

 Reseal bottom cover plate using RTV

silicone sealant.

 Replace compressor.

 Clean compressor and check periodically.

Air brake charging system functioning

normally.

 Air dryers remove water and oil from the air

brake charging system.

Check that regular maintenance is being

performed. Return the vehicle to service.

An optional kit (Bendix piece number

5011327 for the Bendix® AD-IS® or AD-IP™

air dryers, or 5003838 for the Bendix® AD-9™

air dryer) is available to redirect the air dryer

exhaust.

3.0 Oil at air dryer

purge/exhaust or

surrounding area

(c)

2.0 Oil on the

Outside of the

Compressor

Find the source and repair. Return the vehicle

to service.

 Repair or replace as necessary. If the

mounting bolt torques are low, replace the

gasket.

 Replace the ﬁ tting gasket. Inspect inlet

hose and replace as necessary.

 Replace gasket or ﬁ tting as necessary to

ensure good seal.

 Inspect and repair as necessary.

Engine and/or other accessories

leaking onto compressor.

(a) Leak at the front or rear (fuel

pump, etc.) mounting ﬂ ange.

(b) Leak at air inlet ﬁ tting.

(d) Loose/broken oil line ﬁ ttings.

2.1 Oil leaking at

compressor / engine

connections:

Head

gaskets

and rear

ﬂ ange

gasket

locations.

(c)



A-6

Symptom: What it may indicate: What you should do:

4.0 Oil in Supply or

Service Reservoir

(air dryer installed)

(If a maintained Bendix®

PuraGuard® system

ﬁ lter or Bendix®

PuraGuard QC™ oil

coalescing

ﬁ lter is installed, call

1-800-AIR-BRAKE

(1-800-247-2725) and

speak to a Tech Team

member.)

(a) If air brake charging system mainte-

nance has not been performed.

That is, reservoir(s) have not been

drained per the schedule in Table

A on page A-3, Column 4 and/or

the air dryer maintenance has not

been performed as in Column 3.

(b) If the vehicle maintenance has

been performed as recommended

in Table A on page A-3, some oil in

the reservoirs is normal.

 Drain all air tanks and check vehicle at next

service interval using the Bendix® BASIC™

test. See Table A on page A-3, column 3

and 4, for recommended service sched-

ule.

 Drain all air tanks into Bendix® BASIC™ test

cup (Bendix Air System Inspection Cup). If

less than one unit of reservoir contents is

found, the vehicle can be returned to ser-

vice. Note: If more than one oil unit of

water (or a cloudy emulsion mixture) is

present, change the vehicle's air dryer,

check for air system leakage (Test 2, on

page A-14), stop inspection and check

again at the next service interval.

See the BASIC™ test kit for full details.

If less than one "oil unit" of water (or water/

cloudy emulsion mixture) is present, use the

BASIC™cup chart on the label of the cup to

determine if the amount of oil found is within

the acceptable level.

If within the normal range, return the

vehicle to service. For vehicles with acces-

sories that are sensitive to small amounts

of oil, consider a Bendix® PuraGuard QC™

oil coalescing ﬁ lter.

If outside the normal range go to Symp-

tom 4.0(c).

Also see the Table A on page A-3, column

3 for recommended air dryer cartridge

replacement schedule.

Maintenance

 Go to

Test 2 on page A-14.

 See Table A, column 1, on page A-3 for

recommended compressor sizes.

 If the compressor is "too small" for

the vehicle's role (for example, where a

vehicle's use has changed or service condi-

tions exceed the original vehicle or engine

OE spec's) then upgrade the compressor.

Note: The costs incurred (e.g. installing

a larger capacity compressor, etc.) are

not covered under original compressor

warranty.

 If the compressor is correct for the

vehicle, go to Symptom 4.0 (e).

Duty cycle too high

See Table A, on page

A-3, for maintenance

schedule information.

Drain all air tanks (reservoirs)

into the Bendix® BASIC™ test

cup. (Bendix kit P/N 5013711).

The duty cycle is the ratio of time the compressor spends

building air to total engine running time. Air compressors

are designed to build air (to "run loaded") up to 25% of the

time. Higher duty cycles cause conditions that affect air

brake charging system performance which may require

additional maintenance. Factors that add to the duty cycle

are: air suspension, additional air accessories, use of an

undersized compressor, frequent stops, excessive leakage

from ﬁ ttings, connections, lines, chambers or valves, etc.

(d) Compressor may be undersized for

the application.

(a)

A-7

Symptom: What it may indicate: What you should do:

(e) Air compressor discharge and/or

air dryer inlet temperature too

high.

(f) Insufﬁ cient coolant ﬂ ow.

(g) Restricted discharge line.

 Check temperature as outlined in Test 3 on

page A-14. If temperatures are normal go

to 4.0(h).

 Inspect coolant line. Replace as necessary

(I.D. is 1/2").

 Inspect the coolant lines for kinks and

restrictions and ﬁ ttings for restrictions.

Replace as necessary.

 Verify coolant lines go from engine block to

compressor and back to the water pump.

Repair as necessary.

 If discharge line is restricted or more than

1/16" carbon build-up is found, replace the

discharge line. See Table A, column 2, on

page A-3 for recommended size. Replace

as necessary.

 The discharge line must maintain a

constant slope down from the compressor

to the air dryer inlet ﬁ tting to avoid low points

where ice may form and block the ﬂ ow.

If, instead, ice blockages occur at the air

dryer inlet, insulation may be added here,

or if the inlet ﬁ tting is a typical 90 degree

ﬁ tting, it may be changed to a straight or

45 degree ﬁ tting. For more information on

how to help prevent discharge line freeze-

ups, see Bendix Bulletins TCH-08-21

and TCH-08-22 (Appendix B). Shorter

discharge line lengths or insulation may be

required in cold climates.

Temperature

Other

 Check compressor air inlet line for restric-

tions, brittleness, soft or sagging hose

conditions etc. Repair as necessary. Inlet

line size is 3/4 ID. Maximum restriction

requirement for compressors is 25 inches

of water.

 Check the engine air ﬁ lter and service if

necessary (if possible, check the air ﬁ lter

usage indicator).

(h) Restricted air inlet (not enough air

to compressor).

(g)

4.0 Oil in Supply

or Service

Reservoir*

(air dryer installed)

(continued)

Kinked discharge line shown.

Partly

collapsed

inlet line

shown.

Testing the temperature

at the discharge ﬁ tting. Inspecting the coolant hoses.

*If a maintained Bendix® PuraGuard® system ﬁ lter or Bendix® PuraGuard QC™ oil coalescing

ﬁ lter is installed, call 1-800-AIR-BRAKE (1-800-247-2725) and speak to a Tech Team member.

(g)

(e) (f)

(h)

A-8

Symptom: What it may indicate: What you should do:

(i) Poorly filtered inlet air (poor air

quality to compressor).

(j) Governor malfunction or setting.

(k) Compressor malfunction.

4.0 Oil in Supply

or Service

Reservoir*

(air dryer installed)

(continued)

 Check for leaking, damaged or defective

compressor air inlet components (e.g.

induction line, ﬁ ttings, gaskets, ﬁ lter bodies,

etc.). Repair inlet components as needed.

Note: Dirt ingestion will damage compressor

and is not covered under warranty.

 Go to Test 4 on page A-15.

 If you found excessive oil present in the

service reservoir in step 4.0 (b) above and

you did not ﬁ nd any issues in steps 4.0 (c)

through 4.0 (j) above, the compressor may

be passing oil.

Replace compressor. If still under warranty,

follow normal warranty process. Note: After

replacing a compressor, residual oil may

take a considerable period of time to be

ﬂ ushed from the air brake system.

Other (cont.)

Inspect the

engine air

cleaner.

** SAE J2024 outlines tests all air brake system pneumatic

components need to be able to pass, including minimum

levels of tolerance to contamination.

5.0 Oil present

at valves (e.g. at

exhaust, or seen

during servicing).

Air brake system valves are required

to tolerate a light coating of oil.

 A small amount of oil does not affect SAE

J2024** compliant valves.

 Check that regular maintenance is being

performed and that the amount of oil in the

air tanks (reservoirs) is within the accept-

able range shown on the Bendix® BASIC™

test cup (see also column 5 of Table A on

page A-3). Return the vehicle to service.

For oil-sensitive systems, see page 16.

Genuine

Bendix

valves are

all SAE

J2024

compliant.

*If a maintained Bendix® PuraGuard® system ﬁ lter or Bendix® PuraGuard QC™ oil coalescing

ﬁ lter is installed, call 1-800-AIR-BRAKE (1-800-247-2725) and speak to a Tech Team member.

Crankcase Flooding

Consider installing a compressor bottom drain kit

(where available) in cases of chronic oil passing where

all other operating conditions have been investigated.

Bendix compressors are designed to have a 'dry'

sump and the presence of excess oil in the crankcase

can lead to oil carryover.

A-9

Symptom: What it may indicate: What you should do:

8.0 Oil in ping tank

or compressor dis-

charge aftercooler.

Air brake charging system is functioning

normally.

 Air dryers remove water and oil from

the air brake charging system. A small

amount of oil is normal. Check that regular

maintenance is being performed and that

the amount of oil in the air tanks (reservoirs)

is within the acceptable range shown by the

BASIC™ test (see also column 5 of Table

A on page A-3). Replace the air dryer

cartridge as needed and return the vehicle

to service.

7.0 Oil present

at air dryer

cartridge during

maintenance.

A problem with engine or other engine

accessory.

 See engine service manual.

6.0 Excessive oil

consumption in

engine.

Air brake charging system is functioning

normally.

 Follow vehicle O.E. maintenance

recommendation for these components.

(a) Air brake charging system

functioning normally.

(b) Air brake system leakage.

the application.

(d) Compressor unloader mechanism

malfunction.

(e) Damaged compressor head

gasket.

 Using dash gauges, verify that the

compressor builds air system pressure

from 85-100 psi in 40 seconds or less with

engine at full governed rpm. Return the

vehicle to service.

 Go to Test 2 on page A-14.

 See Table A, column 1, on page A-3 for

some typical compressor applications. If the

compressor is "too small" for the vehicle's

role, for example, where a vehicle's use has

changed, then upgrade the compressor.

Note: The costs incurred (e.g. installing

a larger capacity compressor, etc.) are

not covered under original compressor

warranty.

 Go to Test 6 on page A-15.

 An air leak at the head gasket may indi-

cate a downstream restriction such as a

freeze-up or carbon blockage and/or could

indicate a defective or missing safety valve.

Find blockage (go to 9.0(f) for details) and

then replace the compressor. Do not re-

use the safety valve without testing. See

Symptom 12.0(a).

9.0 Air brake

charging system

seems slow to

build pressure.

The engine

service

manual

has more

information.

Oil shown

leaking

from an

air dryer

cartridge.

A-10

Symptom: What it may indicate: What you should do:

(g) Restricted air inlet (not enough air

to compressor).

 Check compressor air inlet line for restric-

tions, brittleness, soft or sagging hose con-

ditions etc. Repair as necessary. Refer to

vehicle manufacturer’s guidelines for inlet

line size.

 Check the engine air ﬁ lter and service if

necessary (if possible, check the air ﬁ lter

usage indicator).

(i) Compressor malfunction.  Replace the compressor only after making

certain that none of the preceding conditions,

9.0 (a) through 9.0 (h), exist.

(h) Poorly filtered inlet air (poor air

quality to compressor).

 Check for leaking, damaged or defective

compressor air inlet components (e.g.

induction line, ﬁ ttings, gaskets, ﬁ lter bodies,

etc.). Repair inlet components as needed.

Note: Dirt ingestion will damage compressor

and is not covered under warranty.

9.0 Air brake

charging system

seems slow to

build pressure.

(continued)

(f) Restricted discharge line.  If discharge line is restricted:

 By more than 1/16" carbon build-up,

replace the discharge line (see Table A,

column 2, on page A-3 for recommended

size) and go to Test 3 on page A-14.

 By other restrictions (e.g. kinks).

Replace the discharge line. See Table A,

column 2, on page A-3 for recommended

size. Re test for air build. Return vehicle

to service or, if problem persists, go to

9.0(a).

 The discharge line must maintain a

constant slope down from the compressor

to the air dryer inlet ﬁ tting to avoid low points

where ice may form and block the ﬂ ow. If,

instead, ice blockages occur at the air dryer

inlet, insulation may be added here, or if the

inlet ﬁ tting is a typical 90 degree ﬁ tting, it

may be changed to a straight or 45 degree

ﬁ tting. For more information on how to

help prevent discharge line freeze-ups, see

Bendix Bulletins TCH-08-21 and TCH-08-22

(Appendix B). Shorter discharge line

lengths or insulation may be required in cold

climates.

Kinked discharge line shown.

Dash gauges.

Partly collapsed

inlet line shown.

(f)

(g)

Engine Oil Quality

Inadequate oil change intervals, the formulation of the

oil and/or the quality of oil ﬁ lter used can all lead to poor

oil quality. These can increase the rate at which carbon

builds up in the discharge line. Bendix recommends oil

soot (solids) be maintained at less than 3%.

A-11

Symptom: What it may indicate: What you should do:

10.0 Air charging

system doesn’t

build air.

(a) Governor malfunction*.

(b) Restricted discharge line.

exhaust port frozen open.

(d) Compressor malfunction.

 Go to Test 4 on page A-15.

 See 9.0(f).

 Replace air dryer heater.

 Replace the compressor only after making

certain the preceding conditions do not

exist.

11.0 Compressor

safety valve

releases air

(Compressor

builds too much

air).

(a) Restricted discharge line.  If discharge line is restricted:

 By more than 1/16" carbon build-up,

replace the discharge line (see Table A,

column 2, on page A-3 for recommended

size) and go to Test 3 on page A-14.

 By other restrictions (e.g. kinks).

Replace the discharge line. See Table A,

column 2, on page A-3 for recommended

size.

 The discharge line must maintain a

constant slope down from the compressor

to the air dryer inlet ﬁ tting to avoid low points

where ice may form and block the ﬂ ow.

If, instead, ice blockages occur at the air

dryer inlet, insulation may be added here,

or if the inlet ﬁ tting is a typical 90 degree

ﬁ tting, it may be changed to a straight or

45 degree ﬁ tting. For more information on

how to help prevent discharge line freeze-

ups, see Bendix Bulletins TCH-08-21

and TCH-08-22 (Appendix B). Shorter

discharge line lengths or insulation may be

required in cold climates.

 Inspect air lines and verify check valves are

operating properly.

 Ensure discharge line is installed into the

inlet of the air dryer and delivery is routed

to the service reservoir.

 Verify relief pressure is 250 psi. Replace if

defective.

 Go to Test 6 on page A-15.

 Go to Test 4 on page A-15.

Damaged

discharge

line shown.

* Note: For the Bendix® DuraFlo™ 596 air compressor, not only

the governor, but also the SV-1™ synchro valve used would

need to be tested. See Bulletin TCH-001-048.



(b) Downstream air brake system check

valves or lines may be blocked or

damaged.

(d) Compressor safety valve

malfunction.

(e) Compressor unloader mechanism

malfunction.

(f) Governor malfunction.

A-12

Symptom: What it may indicate: What you should do:

15.0 Compressor

constantly cycles

(compressor

remains unloaded

for a very short

time.)

(a) Air brake charging system

maintenance not performed.

(b) Compressor unloader mechanism

malfunction.

check valve malfunction.

(d) Air brake system leakage.

 Available reservoir capacity may be

reduced by build-up of water etc. Drain and

perform routine maintenance per Table A,

columns 3 & 4, on page A-3.

 Go to Test 6 on page A-15.

 Verify operation of air dryer. Follow vehicle

O.E. maintenance recommendations and

component Service Data information.

 Go to Test 2 on page A-14.

14.0 Air dryer

doesn’t purge.

(Never hear

exhaust from air

dryer.)

(a) Air dryer malfunction.

(b) Governor malfunction.

(d) Improper governor control line

installation to the reservoir.

 Verify operation of air dryer. Follow vehicle

O.E. maintenance recommendations.

 Go to Test 4 on page A-15.

 Go to Test 2 on page A-14.

 Go to Test 5 on page A-15.

12.0 Air dryer

safety valve

releases air.

(a) Restriction between air dryer and

reservoir.

(b) Air dryer safety valve

malfunction.

performed.

(d) Air dryer malfunction.

(e) Improper governor control line

installation to the reservoir.

(f) Governor malfunction.

 Inspect delivery lines to reservoir for

restrictions and repair as needed.

 Verify relief pressure is at vehicle or

component manufacturer speciﬁ cations.

Replace if defective.

 See Maintenance Schedule and Usage

Guidelines (Table A, column 3, on page

A-3).

 Verify operation of air dryer. Follow vehicle

O.E. maintenance recommendations and

component Service Data information.

 Go to Test 5 on page A-15.

 Go to Test 4 on page A-15.

13.0 Reservoir

safety valve

releases air

(a) Reservoir safety valve

malfunction.

(b) Governor malfunction.

malfunction.

 Verify relief pressure is at vehicle or

component manufacturer's speciﬁ cations

(typically 150 psi). Replace if defective.

 Go to Test 4 on page A-15.

 Go to Test 6 on page A-15.

Technician removes

governor.



Air dryer

safety valve



A-13

Symptom: What it may indicate: What you should do:

This guide attempts to cover most com-

pressor system problems. Here are some

rare sources of problems not covered in

this guide:

• Turbocharger leakage. Lubricating

oil from leaking turbocharger seals can

enter the air compressor intake and give

misleading symptoms.

• Where a compressor does not have

a safety valve installed, if a partial or

complete discharge line blockage has

occurred, damage can occur to the con-

necting rod bearings. Damage of this kind

may not be detected and could lead to

compressor problems at a later date.

17.0 Compressor

leaks coolant (a) Improperly installed plugs or coolant

line ﬁ ttings.

(b) Damaged compressor head

gasket.

 Inspect for loose or over-torqued ﬁ ttings.

Reseal and tighten loose ﬁ ttings and plugs

as necessary. If overtorqued ﬁ ttings and

plugs have cracked ports in the head,

replace the compressor.

 An air leak at the head gasket may indicate

a downstream restriction such as a freeze-

up or carbon blockage and/or could indicate

a defective or missing safety valve. Find

blockage (go to 9.0(f) for details) and then

replace the compressor. Do not re-use the

safety valve without testing. See Symptom

12.0(a).

 If casting porosity is detected, replace the

compressor.

18.0 Noisy

compressor

(Multi-cylinder

compressors only)

(a) Damaged compressor.  Replace the compressor.

Testing for leaks with

soap solution.

16.0 Compressor

leaks air (a) Compressor leaks air at connections

or ports.

(b) Compressor unloader mechanism

malfunction.

gasket(s).

 Check for leaking, damaged or defective

compressor ﬁ ttings, gaskets, etc. Repair

or replace as necessary.

 Go to Test 6 on page A-15.

 An air leak at the head gasket(s) may

indicate a downstream restriction such as a

freeze-up or carbon blockage and/or could

indicate a defective or missing safety valve.

Find blockage (go to 9.0(f) for details) and

then replace the compressor. Do not re-

use the safety valve without testing. See

Symptom 12.0(a).

Other Miscellaneous Areas to Consider

Head gasket

location



A-14

Tests

Exterior leaks at the head gasket are not a sign that oil is being passed into

the air charging system. Oil weepage at the head gasket does not prevent

the compressor from building air.

Observe the amount of weepage from the head gasket.

If the oil is only around the cylinder head area, it is acceptable (return the vehicle

to service), but, if the oil weepage extends down to the nameplate area of the

compressor, the gasket can be replaced.

Test 1: Excessive Oil Leakage at the

Head Gasket

Inspect for air leaks when working on a vehicle and

repair them promptly.

Park the vehicle on level ground and chock wheels.

Build system pressure to governor cut-out and allow

the pressure to stabilize for one minute.

Step 1: Observe the dash gauges for two additional

minutes without the service brakes applied.

Step 2: Apply the service brakes and allow the

pressure to stabilize. Continue holding for two

minutes (you may use a block of wood to hold the

pedal in position.) Observe the dash gauges.

If you see any noticeable decrease of the dash air

gauge readings (i.e. more than 4 psi, plus two psi

for each additional trailer) during either two minute

test, repair the leaks and repeat this test to conﬁ rm

that they have been repaired.

Air leaks can also be found in the charging system,

parking brakes, and/or other components - inspect

and repair as necessary.

Test 2: Air Brake System and Accessory Leakage

Caution: The temperatures used in this test

are not normal vehicle conditions.

Above normal temperatures can cause oil (as

vapor) to pass through the air dryer into the

air brake system.

This test is run with the engine at normal operating

temperature, with engine at max. rpm. If

available, a dyno may be used.

1. Allow the compressor to build the air system

pressure to governor cut-in.

2. Pump the brakes to bring the dash gauge

pressure to 90 psi.

3. Allow the compressor to build pressure from

95 to 105 psi gauge pressure and maintain

this pressure range by cycling the brakes for

ﬁ ve (5) minutes.

4. Then, while maintaining max rpm and

pressure range, measure and record the

surface temperature of the ﬁ ttings:

 at the compressor discharge port. (T1).

 at the air dryer inlet ﬁ tting. (T2).

Use a touch probe thermocouple for measuring

the temperature.

5. See table below.

6. Re test before returning the vehicle to

service.

Test 3: Air Compressor Discharge

Temperature and Air Dryer Inlet

Temperature*

Compressor Air Dryer

Discharge Inlet

Fitting Fitting

Action

under under Temperatures are within

360°F 200°F normal range for this test, check

other symptoms. Go to 4.0 (h).

under over This could indicate a discharge

360°F 200°F line problem (e.g. restriction).

Call 1-800-AIR-BRAKE

(1-800-247-2725)

and speak with our Tech Team.

over __ Compressor is running hot.

360°F Check coolant 4(f) and/or

discharge line 4(g).

T1 T2

(* Note that only vehicles that have passed Test 2

would be candidates for this test.)

Discharge Line

Look

for

Weepage

A-15

1. Ensure that the governor control line from the

reservoir is located at or near the top of the res-

ervoir. (This line, if located near the bottom of

the reservoir, can become blocked or restricted

by the reservoir contents e.g. water or ice.)

Bendix® Compressors: Park vehicle, chock

wheels, and follow all standard safety procedures.

Remove the governor and install a ﬁ tting to the

unloader port. Add a section of air hose (min

1 ft long for a 1/2" diameter line) and a gauge

to the ﬁ tting followed by a shut-off valve and an

air source (shop air or small air tank). Open the

Test 5: Governor Control Line

Test 6: Compressor Unloader Leakage

1. Inspect control lines to and from the governor

for restrictions (e.g. collapsed or kinked).

Repair as necessary.

2. Using a calibrated external gauge in the

supply reservoir, service reservoir, or reservoir

port of the D-2™ governor, verify cut-in and

cut-out pressures are within vehicle OEM

speciﬁ cation.

3. If the governor is malfunctioning, replace it.

Tests (continued)

Test 4: Governor Malfunction

2. Perform proper reservoir drain intervals and air

dryer cartridge maintenance per Maintenance

Schedule and Usage Guidelines (Table A on

page A-3).

3. Return the vehicle to service.

shut-off and charge the unloader port by allowing

air pressure to enter the hose and unload the

compressor. Shut off the air supply and observe

the gauge. A steady reading indicates no leakage

at the unloader port, but a falling reading shows

that the unloader mechanism is leaking and needs

to be serviced.

A-16

High

START BASIC TEST

Is this a

transit vehicle, bulk

unloader, or has more

than 5 axles?

YES, this is a high

air use

vehicle.

NO, this is a low air

use vehicle.

Park vehicle on ground.LEVEL

Chock wheels, drain air from system.

Drain contents of air

tanks into

ALL

BASIC cup

™

• water, or

• cloudy emulsion

mixture?

Is this vehicle

being re-tested? (after

water, etc. was found

last time?)

YES

Is the

point above

the HIGH Air Use

line on the

cup?

YES

Does

the vehicle have

excessive air

leakage?

Repair leaks and

return vehicle to

service

Is there

less than one

unit of liquid?

END TEST

Vehicle OK.

Return vehicle to

service.

YES

NO, only oil.

Vehicle OK.

Return vehicle to

service.

Find the point on the label

where the number of oil units

meets the number of days*

since the vehicle's air tanks

were last drained.

Is the

point above

the LOW Air Use

line on the

cup?

YES

END TEST

Compressor

Change air dryer

cartridge**

Re-test with the

BASIC Test after

™

30 days***

Test for air

leakage

Find the point on the label

where the number of oil units

meets the number of days*

since the vehicle's air tanks

were last drained.

Cloudy emulsion mixture

Go to the

Advanced

Troubleshooting

Guide to find

reason(s) for

presence of water

END TEST

Test for air

leakage

END TEST

there more

than one unit of:

High

Low

High

Service writer records info - including

the number of days since all air tanks

were ills out symptom

checklist. Technician inspects items.

drained - and f

days

Use Test 2:

Air Leakage

Use Test 2:

Air Leakage

Re-test with the

BASIC Test after

™

30 days***

NO (did not know

when last

drained)

Was

the number of

days since last

draining

known?

YES, number of days

was known (30 - 90 days)

END TEST

Bendix® Air System Inspection Cup

(BASIC™) Test Information

Appendix B: Information about the BASIC™ Test Kit (Bendix P/N 5013711)

* If the number of days since the air tanks were drained is unknown

- use the 30 day line.

** Note: Typical air dryer cartridge replacement schedule is every

3 yrs/ 300K miles for low air use vehicles and every year/100K

miles for high air use vehicles.

*** To get an accurate reading for the amount of oil collected during

a 30 day period, ask the customer not to drain the air tanks before

returning. (Note that 30-90 days is the recommended air tank

drain schedule for vehicles equipped with a Bendix air dryer that

is properly maintained.) If, in cold weather conditions, the 30 day

air tank drain schedule is longer than the customer's usual draining

interval, the customer must determine, based on their experience

with the vehicle, whether to participate now, or wait for warmer

weather. See the cold weather tips in Bulletins TCH-008-21 and

TCH-008-22 (included on pages A-19-21 of this document).

****Note: After replacing a compressor, residual oil may take

a considerable period of time to be ﬂ ushed from the air brake

system.

Replace the Compressor. If under warranty, follow standard

procedures.

If, after a compressor was already replaced, the vehicle fails the

BASIC™ test again, do not replace the compressor**** - use the

Advanced Troubleshooting Guide to investigate the cause(s).

A-17

Footnote 1: Note: Typical air dryer cartridge replacement schedule is every 3 yrs/ 300K miles for low air use vehicles and every year/100K miles for

high air use vehicles.

Footnote 2: To get an accurate reading for the amount of oil collected during a 30 day period, ask the customer not to drain the air tanks before returning.

(Note that 30-90 days is the recommended air tank drain schedule for vehicles equipped with a Bendix air dryer that are properly maintained.) If, in cold

weather conditions, the 30 day air tank drain schedule is longer than the customer's usual draining interval, the customer must determine, based on its

experience with the vehicle, whether to participate now, or wait for warmer weather. See the cold weather tips in Bulletins TCH-008-21 and TCH-008-22

(included in Appendix B of the advanced troubleshooting guide).

Note for returning vehicles that are being

re tested after a water/cloudy emulsion

mixture was found last time and the air

dryer cartridge replaced: If more than one

oil unit of water or a cloudy emulsion mixture

is found again, stop the BASIC™ test and

consult the air dryer's Service Data sheet

troubleshooting section.

* Note: A conﬁ rmed complaint

above does NOT mean that

the compressor must be

replaced.

The full BASIC™ test below

will investigate the facts.

Customer’s Have you conﬁ rmed

complaint?

(Please check all that apply)

“Relay valve  leaks oil /  malfunctions”  no  yes*

“Dash valve  leaks oil /  malfunctions”  no  yes*

 “Air dryer leaks oil”  no  yes*

 “Governor malfunction”  no  yes*

 “Oil in gladhands”  no  yes*

how much oil did you ﬁ nd? ________________________________

 “Oil on ground or vehicle exterior”  no  yes*

amount described: ______________________________________

 “Short air dryer cartridge life”

replaces every: ______________  miles,  kms, or  months

 “Oil in air tanks” amount described:_______________________

We will measure amount currently found when we get to step B of the test.

 “Excessive engine oil loss” amount described: ______________

Is the engine leaking oil?  no  yes*

Is the compressor leaking oil?  no  yes*

 Other complaint: _____________________________________

 No customer complaint.

Checklist for Technician



The Service Writer ﬁ lls out these ﬁ elds with information gained from the customer

The Service Writer

also checks off any

complaints that the

customer makes to

help the Technician

in investigating.

The Technician

checks boxes

for any of the

complaints that

can be conﬁ rmed.

STEP A - Select one:

BASIC™ test starts here:

STEP B - Measure the Charging System Contents

The Technician selects the air use

category for the vehicle. This decides

which of the two acceptance lines

on the cup will be used for the test

below.

For an accurate test, the

contents of all the air tanks on

the vehicle should be used.

Then go to Step B.

Number of Days Since Air Tanks Were Last Drained: ________ Date: ___________Vehicle #: ____________

Engine SN __________________________ Vehicle Used for: _______________Typical Load:________ (lbs.)

No. of Axles: ____ (tractor) ____ (trailer) No. of Lift Axles: ____ Technician’s Name: ____________________

 This is a low air use vehicle: Line haul (single trailer) with 5 or less axles, or

 This is a high air use vehicle: Garbage truck, transit bus, bulk unloader, or line

haul with more than 5 axles.

1. Park and chock vehicle on level ground. Drain the air system by

pumping the service brakes.

2. Completely drain ALL the air tanks into a single BASIC™cup.

3. If there is less than one unit of contents total, end the test now and

return the vehicle to service. Vehicle passes.

4. If more than one oil unit of water (or a cloudy emulsion mixture)

is found:

Otherwise, go to Step C.

Filling in the Checklist for the Bendix® Air System Inspection Cup (BASIC™) Test

Note: Follow all standard safety precautions. For vehicles using a desiccant air dryer.

Appendix B continued: Information about the BASIC™Test Kit (Bendix P/N 5013711)

(a) Change the vehicle’s air dryer cartridge

- see Footnote 1,

(b) Conduct the 4 minute leakage test (Step D),

again after 30 days - see Footnote 2. STOP

+ CK.

Oil

Units

A-18

Park the vehicle on level ground and chock wheels. Build system pressure to governor cut-out

and allow the pressure to stabilize for one minute.

1: Observe the dash gauges for two additional minutes without the service brakes applied.

2: Apply service brakes for two minutes (allow pressure to stabilize) and observe the dash

gauges.

If you see any noticeable decrease of the dash air gauge readings, repair leaks. Repeat

this test to conﬁ rm that air leaks have been repaired and return vehicle to service. Please

repeat BASIC™ test at next service interval. Note: Air leaks can also be found in the charging

system, parking brakes, and/or other components - inspect and repair as necessary.

STEP E - If no air leakage was detected in Step D

STEP D - Air Brake System Leakage Test

STEP C - How to Use the BASIC™ Test

Sixty days since last air

tank draining Decision point

The Technician uses the chart (label) on the BASIC™

test cup to help decide the action to take, based on

the amount of oil found. Use the lower acceptance

line for low air use vehicles, and upper line for high

air use vehicles (from Step A).

If no air leakage was detected, and if you are conducting

this test after completing Step C, go to Step E.

BASIC™ Test Example

An oil level of 4 units in a sixty-day period is within the

acceptance area (at or below the line) for both low and

high air use vehicles. Return the vehicle to service.

1. Record days since air

tanks were last drained.



3. Action to

take

2. Record amount

of oil found:

If number of days is:

30-60 days (high air

use) or

30-90 days (low air

use)



if oil level is at or below

acceptance line for number

of days

if oil level is above

acceptance line for number

of days 

System OK.

Return to service.

Otherwise . . .



(if the number of days is

unknown, or outside the

limits above)

if oil level is at or below

30-day acceptance line 

if oil level is above 30-day

acceptance line 

STOP

TEST

Stop inspection.

Test again

after 30 days.

See Footnote 2.

_________ days _________ units

Go to Step D

System OK.

Return to service.STOP

TEST

STOP

+ CK.

The Technician looks for the point where the number

of days since the air tanks were drained meets the oil

level. If it is at or below the (low or high use) acceptance

line, the vehicle has passed the test. If the point is

above the line then go to the leakage test. Air leakage is the number one

cause of compressors having

to pump excessive amounts of

air, in turn run too hot and pass

oil vapor along into the system.

Here the Technician conducts a

four-minute test to see if leakage

is a problem with the vehicle

being tested.

The Technician only reaches

Step E if the amount of oil

found, or the amount of time

since the air tanks were last

drained exceeds the acceptance

level, AND the vehicle passes

the four-minute leakage test

(no noticeable leakage was

detected).

Replace the compressor.

Note: If the compressor is within warranty period,

please follow standard warranty procedures. Attach

the completed checklist to warranty claim.

Filling in the Checklist for the Bendix® Air System Inspection Cup (BASIC™) Test

Note: Follow all standard safety precautions. For vehicles using a desiccant air dryer.

Appendix B continued: Information about the BASIC™Test Kit (Bendix P/N 5013711)

Oil

Level

Acceptance

Lines

A-19

Technical Bulletin

Bulletin No.: TCH-008-021 Effective Date: 11/1/92

Page: 1 of 2

Subject: Air Brake System - Cold Weather Operation Tips

As the cold weather approaches, operators and ﬂ eets alike begin to look to their vehicles with an eye

toward “winterization”, and particularly what can be done to guard against air system freeze-up. Here

are some BASIC™“Tips” for operation in the cold weather.

Engine Idling

Avoid idling the engine for long periods of time! In addition to the fact that most engine manufacturers

warn that long idle times are detrimental to engine life, winter idling is a big factor in compressor discharge line

freeze-up. Discharge line freeze-ups account for a signiﬁ cant number of compressor failures each year. The

discharge line recommendations under “Discharge Lines” are important for all vehicles but are especially so

when some periods of extended engine idling can not be avoided.

Discharge Lines

The discharge line should slope downward from the compressor discharge port without forming water traps,

kinks, or restrictions. Cross-overs from one side of the frame rail to the other, if required, should occur as close

as possible to the compressor. Fitting extensions must be avoided. Recommended discharge line lengths and

inside diameters are dependent on the vehicle application and are as follows.

Typical P&D, School Bus and Line Haul

The maximum discharge line length is 16 feet.

Length I.D. Min. Other Requirements

6.0-9.5 ft. ½ in. None

9.5-12 ft. ½ in. Last 3 feet, including ﬁ tting at the end of the

discharge line, must be insulated with ½ inch thick closed

cell polyethylene pipe insulation.

12-16 ft. 5/8 in. Last 3 feet, including ﬁ tting at the end of the

discharge line, must be insulated with ½ inch thick

closed cell polyethylene pipe insulation.

If the discharge line length must be less than 6 feet or greater than 16 feet, contact your local Bendix

representative.

Appendix C

A-20

Bulletin No.: TCH-008-021 Effective Date: 11/1/92

Page: 2 of 2

High Duty Cycle Vehicles (City Transit Coaches, Refuse Haulers, Etc.)

The maximum discharge line length is 16 feet.

Length I.D. min. Other Requirements

10-16 ft. ½ in. None

If the discharge line length must be less than 10 feet or greater than 16 feet, contact your local Bendix

representative.

System Leakage

Check the air brake system for excessive air leakage using the Bendix “Dual System Air Brake Test and Check

List” (BW1279). Excessive system leakage causes the compressor to “pump” more air and also more moisture

into the brake system.

Reservoir Draining (System Without Air Dryer)

Routine reservoir draining is the most BASIC™step (although not completely effective) in reducing the possibility

of freeze-up. All reservoirs in a brake system can accumulate water and other contamination and must be

drained! The best practice is to drain all reservoirs daily. When draining reservoirs; turn the ENGINE OFF and

drain ALL AIR from the reservoir, better still, open the drain cocks on all reservoirs and leave them open over

night to assure all contamination is drained (reference Service Data Sheet SD-04-400 for Bendix Reservoirs).

If automatic drain valves are installed, check their operation before the weather turns cold (reference Service

Data Sheet SD-03-2501 for Bendix® DV-2™ Automatic Drain Valves). It should be noted that, while the need

for daily reservoir draining is eliminated through the use of an automatic drain valve, periodic manual draining

is still required.

Alcohol Evaporator or Injector Systems

Check for proper operation of these systems by monitoring alcohol consumption for a few days (Reference

Service Data Sheet SD-08-2301 for the Bendix Alcohol Evaporator). Too little means the system is not receiving

adequate protection and too much simply wastes alcohol. As a general guide, these systems should consume

approximately 1 to 2 ounces of alcohol per hour of compressor loaded time (compressing air). City pick-up

and delivery vehicles will operate with the compressors loaded (compressing air) more while compressors on

highway vehicles will be loaded less. These ﬁ gures are approximate and assume that air system leakage is

within the limits of the Bendix “Dual System Air Brake Test and Check List” (BW1279). Last but not least, begin

using alcohol several weeks prior to freezing weather to ensure that the system is completely protected. Use

only methanol alcohol, such as Bendix “Air Guard”, in evaporators or injectors.

Air Dryers

Make certain air brake system leakage is within the limits stated in BW1279. Check the operation and function

of the air dryer using the appropriate Service Data Sheet for the air dryer.

AD-9™ Air Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service Data Sheet SD-08-2412

AD-4™ Air Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service Data Sheet SD-08-2407

AD-2™ Air Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service Data Sheet SD-08-2403

AD-IP™ Air Dryer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service Data Sheet SD-08-2414

AD-SP™ Air Dryer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Service Data Sheet SD-08-2415

Trailer System-Guard® Air Dryer. . . . . . . . . . . . . . . . . . . . . . Service Data Sheet SD-08-2416

Bendix® PuraGuard QC™ Oil Coalescing Filter. . . . . . . . . . . Service Data Sheet SD-08-187B

Appendix C: Continued

A-21

Technical Bulletin

Bulletin No.: TCH-008-022 Effective Date: 1/1/1994

Page: 1 of 1

Subject: Additional Cold Weather Operation Tips for the Air Brake System

Last year we published Bulletin PRO-08-21 which provided some guidelines for “winterizing” a

vehicle air brake system. Here are some additional suggestions for making cold weather vehicle

operation just a little more bearable.

Thawing Frozen Air Lines

The old saying; “Prevention is the best medicine” truly applies here! Each year this activity accounts

for an untold amount of unnecessary labor and component replacement. Here are some Do’s and

Don’ts for prevention and thawing.

Do’s

1. Do maintain freeze prevention devices to prevent road calls. Don’t let evaporators or injectors run

out of methanol alcohol or protection will be degraded. Check the air dryer for proper operation

and change the desiccant when needed.

2. Do thaw out frozen air lines and valves by placing the vehicle in a warmed building. This is the

only method for thawing that will not cause damage to the air system or its components.

3. Do use dummy hose couplings on the tractor and trailer.

4. Do check for sections of air line that could form water traps. Look for “drooping” lines.

Don’ts

1. Do not apply an open ﬂ ame to air lines and valves. Beyond causing damage to the internal

nonmetallic parts of valves and melting or burning non-metallic air lines. WARNING: THIS

PRACTICE IS UNSAFE AND CAN RESULT IN VEHICLE FIRE!

2. Do not introduce (pour) ﬂ uids into air brake lines or hose couplings (“glad hands”). Some ﬂ uids

used can cause immediate and severe damage to rubber components. Even methanol alcohol,

which is used in Alcohol Evaporators and Injectors, should not be poured into air lines. Fluids

poured into the system wash lubricants out of valves, collect in brake chambers and valves and

can cause malfunction. Loss of lubricant can affect valve operating characteristics, accelerate

wear and cause premature replacement.

3. Do not park a vehicle outside after thawing its air system indoors. Condensation will form in the

system and freeze again. Place the vehicle in operation when it is removed to the outdoors.

Supporting Air and Electrical Lines

Make certain tie wraps are replaced and support brackets are re-assembled if removed during routine

maintenance. These items prevent the weight of ice and snow accumulations from breaking or

disconnecting air lines and wires.

Automatic Drain Valves (System without Air Dryer)

As we stated last year, routine reservoir draining is the most BASIC™step (although not completely

effective) in reducing the possibility of freeze-up. While automatic drain valves relieve the operator

of draining reservoirs on a daily basis, these valves MUST be routinely checked for proper operation.

Don’t overlook them until they fail and a road call is required.

Appendix D

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