Bendix Tu Flo 400 500 1000 Air Compressor Users Manual ManualsLib Makes It Easy To Find Manuals Online!

: Bendix Bendix-Tu-Flo-400-500-1000-Air-Compressor-Users-Manual-119041 bendix-tu-flo-400-500-1000-air-compressor-users-manual-119041 bendix pdf

Open the PDF directly: View PDF .
Page Count: 40

Download
Open PDF In Browser	View PDF

SD-01-326

®

Bendix® TU-FLO® 400, 500, 1000 Air Compressors

TU-FLO® 400 Air Compressor

TU-FLO® 500 Air Compressor

TU-FLO® 1000 Air Compressor
1

DESCRIPTION AND OPERATION
GENERAL
The function of the air compressor is to build up and maintain
the air pressure required to operate air powered devices in
air brake or air auxiliary systems.

and they have no external moving parts. Both air and water
cooled type compressors are available. Various mounting
and drive adaptations are used as required by different vehicle
engine designs (Fig. 4).

DESCRIPTION
Tu-Flo® Type 400, 500, and 1000 compressors are single
stage, reciprocating piston type compressors. Tu-Flo® 400
(Fig. 1) and 500 (Fig. 2) compressors have two cylinders
while the Tu-Flo® 1000 compressor (Fig. 3) is a V-type
design having four cylinders. The rated capacity of all Bendix
compressors is their piston displacement in cubic feet per
minute when operating at 1,250 RPM. The rated capacity
of the Tu-Flo® 400 compressor is 7-1/4 cubic feet per minute.
The Tu-Flo® 500 compressor is rated at 12 cubic feet per
minute and the Tu-Flo® 1000 compressor has a rating of 24
cubic feet per minute.
Tu-Flo® type compressors have automatic type inlet valves.
Their unloading mechanisms are located in the cylinder block

FIGURE 1 - TU-FLO® 400 AIR COMPRESSOR
FIGURE 4 - VARIOUS COMPRESSOR MOUNTINGS

Compressors are either engine or self-lubricated. The
majority used are the engine lubricated types (Fig. 5) which
obtain the oil necessary to lubricate their moving parts from
the engines on which they are mounted. To meet the
requirements of some manufacturers and for field
installations, self-lubricated types (Fig. 6) are available. They
are compressors having a self-contained oil supply and
pumping system.
FIGURE 2 - TU-FLO® 500 AIR COMPRESSOR

FIGURE 3 - TU-FLO® 1000 AIR COMPRESSOR
2

The method of lubricating the moving parts of the compressor
is the same in either type. Oil is forced through the oil
passage in the crankshaft and out around each connecting
rod journal. The turning motion of the crankshaft throws the
oil that is forced out at the journals, against the cylinder
bores and crankcase walls, lubricating the bores and
crankshaft bearings.
The wrist pins and wrist pin bushings are lubricated in two
ways depending upon the type connecting rods used. Older
design compressors had forged steel rifle-drilled rods through
which oil was forced to the wrist pin bushings. Later versions

OPERATION
GENERAL

FIGURE 5
ENGINE LUBRICATED TYPE

FIGURE 6
SELF-LUBRICATED TYPE

had either die cast aluminum, cast ductile iron, or forged
steel rods which were not rifle drilled but were drilled at the
top of the rod. The wrist pins and bushings are lubricated
by oil dripping from a drip-boss on the piston into a
“catch-funnel” at the top of the rod and through the drilled
passage to the bushings and pins. (SEE FIG. 7)

All compressors run continuously while the engine is running,
but actual compression of air is controlled by a governor,
which stops or starts the compression of air by loading or
unloading the compressor in conjunction with its unloading
mechanism. This is done when the air pressure in the system
reaches the desired maximum or minimum pressures.

TO RESERVOIR
INLET VALVE
UNLOADER PLUNGER

DISCHARGE
VALVE
PISTON

INTAKE
STRAINER

WRIST PIN
BUSHING

PISTON WRIST PIN
LOCK WIRE

TO GOVERNOR

CAST IRON
PISTON

WRIST PIN

STROKE
INTAKE

OIL
PASSAGE

STEEL
CONNECTING
ROD
OLD DESIGN
“CATCH FUNNEL”

WRIST PIN
BUSHING
DIE CAST
PISTON
DIE CAST
CONNECTING ROD
NEW DESIGN
FIGURE 7- PISTONS & CONNECTING RODS

A nameplate is attached to the crankcase of all compressors.
It shows the piece number, type and serial number (Fig. 8).
A nameplate with a black background denotes a new
compressor, whereas a nameplate with a red background
designates that the compressor is a factory reconditioned
unit. All compressors are identified by the piece number
which is the number to use when reference is made to a
particular compressor. The type and serial number is
supplementary information.

FIGURE 9

INTAKE AND COMPRESSION (Loaded)
During the down stroke of the piston, a slight vacuum created
above the piston causes the inlet valve to move off its seat.
Atmospheric air is drawn in through the compressor intake,
by the open inlet valve, and on top of the piston (Fig. 9). As
the piston starts its upward stroke, the air that was drawn in
on the down stroke is being compressed. Now, air pressure
on top of the inlet valve plus the force of its spring, returns
the inlet valve to its seat. The piston continues the upward
stroke and compresses the air sufficiently to overcome the
discharge valve spring and unseat the discharge valve. The
compressed air then flows by the open discharge valve, into
the discharge line and on to the reservoirs (Fig. 10).

TO RESERVOIR
INLET VALVE
UNLOADER PLUNGER

DISCHARGE
VALVE

INTAKE
STRAINER

PISTON

TO GOVERNOR
STROKE
COMPRESSION
FIGURE 8 - COMPRESSOR NAMEPLATE

FIGURE 10
3

As the piston reaches the top of its stroke and starts down,
the discharge valve spring 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.
NON-COMPRESSION (Unloaded)
When the air pressure in the reservoir reaches the high
pressure setting of the governor, the governor opens, allowing
air to pass from the reservoir through the governor and into
the cavity beneath the unloader pistons. This lifts the
unloader pistons and plungers. The plungers move up and
hold the inlet valves off their seats (Fig. 11).

TO RESERVOIR
INLET VALVE
UNLOADER
PLUNGER

DISCHARGE
VALVE
PISTON

INTAKE
STRAINER
TO GOVERNOR
STROKE
UNLOADING
FIGURE 11

With the inlet valves held off their seats by the unloader
pistons and plungers, air is merely pumped back and forth
between the two cylinders. When air is used from the
reservoir and the pressure drops to the low pressure setting
of the governor, the governor closes, and in doing so,
exhausts the air from beneath the unloader pistons. The
unloader saddle spring forces the saddle, pistons and
plungers down 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
specifically, 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.
Powered by the vehicle engine, the air compressor builds
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
4

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
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 fittings, 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 fitting or reservoir
to avoid low points where ice may form and block the flow. If,
instead, ice blockages occur at the air dryer or reservoir
inlet, insulation may be added here, or if the inlet fitting is a
typical 90 degree fitting, it may be changed to a straight or
45 degree fitting. 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 installed
in the cylinder head 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 oilvapor 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 Brake Charging System supplies the
Discharge
Line

Optional “Ping” Tank
Air Dryer

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.
Optional Bendix® PuraGuard ® QC™
Oil Coalescing Filter

Compressor
Governor
(Governor plus Synchro valve
for the Bendix® DuraFlo™ 596
Compressor)

Service Reservoir
(Supply Reservoir)

Reservoir Drain
FIGURE 12A - SYSTEM DRAWING

PREVENTIVE MAINTENANCE

HOLE

THREAD

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.
If the compressor is a self-lubricated type, its oil level should
be checked daily. The oil level should be kept between the
bottom of the dipstick threads and the bottom of the dipstick
(Fig. 13). Every 8,000 miles or 300 operating hours, the oil
should be drained and refilled with SAE 10-20-30.

FIGURE 12B - DISCHARGE LINE SAFETY VALVE

The air dryer contains a filter 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 recommend installation of a Bendix®
PuraGuard® QC™ oil coalescing filter, designed to minimize
the amount of oil present.
COOLING
Tu-Flo® 400, 500 or 1000 compressors may be air-cooled or
water- cooled and in some instances will have air-cooled
blocks and water-cooled heads. The air-cooled versions
are easily recognized by the external fins. The water-cooled
versions are cooled by vehicle coolant.

FIGURE 13 - OIL LEVEL - SELF-LUBRICATED
COMPRESSOR

POLYURETHANE SPONGE STRAINER (Fig. 14)
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 air strainer is removed from the compressor intake.
5

FIGURE 16 - COMPRESSOR INTAKE ADAPTER
FIGURE 14 - POLYURETHANE SPONGE STRAINER

AIR LEAKAGE TESTS
Leakage past the discharge valves can be detected by
removing the discharge line, applying shop air back through
the discharge port and listening for escaping air. Also the
discharge valves and the unloader pistons can be checked
for leakage by building up the air system until the governor
cuts out, then stopping the engine. With the engine stopped,
carefully listen for escaping air at the intake. To pinpoint
leakage if noted, squirt oil around the unloader pistons. If
there is no noticeable leakage at the unloader pistons, the
discharge valves may be leaking.

FIGURE 15 - DRY ELEMENT- PLEATED PAPER AIR
STRAINER

DRY ELEMENT - PLEATED PAPER AIR
STRAINER (FIG. 15)
Remove the spring clips from either side of mounting baffle
and remove the cover. Replace the pleated paper filter and
remount the cleaned cover making sure the filter is in
position. Be sure to replace the air strainer gasket if the
entire air strainer is removed from the compressor intake.
(NOTE: Some compressors are fitted with compressor intake
adapters (Fig. 16) which allow the compressor intake to be
connected to the engine air cleaner.) In this case, the
compressor receives a supply of clean air from the engine
air cleaner. When the engine air filter 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 air
cleaner. Inspect the connecting line for ruptures and replace
it if necessary.

6

If the compressor does not function as described above, or
leakage is excessive, it is recommended that it be returned
to the nearest Bendix authorized distributor for a factory
rebuilt compressor under the repair exchange plan. If this is
not possible, the compressor can be repaired with genuine
Bendix parts, in which case the following information should
prove helpful.

REMOVING AND INSTALLING
REMOVING
These instructions are general and in some cases additional
precautions must be taken.
Drain air brake system.
If water-cooled type compressor, drain engine cooling
system, compressor cylinder head and block.
Disconnect all air lines, water and oil lines to and from
compressor.
Remove compressor mounting bolts and compressor from
engine.
Use a gear-puller to remove the gear or pulley from
compressor crankshaft.
INSTALLATION
ENGINE-LUBRICATED TYPES
Clean oil supply line. Before connecting this line to the
compressor, run the engine briefly to be sure oil is flowing
freely through the supply line.
Clean the oil return line or return passages through the
brackets; these passages must be unrestricted so oil can
return to the engine.

Prelubricate compressor cylinder walls and bearings with
clean engine oil before assembling compressor.
Always use a new mounting gasket and be sure oil hole in
gasket and compressor is properly aligned with oil supply
line.
SELF-LUBRICATED TYPES
Fill compressor crankcase with clean engine oil before
operating compressor. Refer to “Tabulated Data” section for
proper amount.
ALL TYPES
Inspect pulley or gear and associated parts for wear or
damage. They must be a neat fit on compressor crankshaft.
Replace pulley or gear if worn or damaged.
Install pulley or gear on compressor crankshaft making sure
it properly contacts the shaft and does not ride the key.
Tighten crankshaft nut to 65-70 ft. lbs. and install cotter
pin.
Be sure the air cleaner is clean and properly installed. If the
compressor intake is connected to either the engine air
cleaner or supercharger, these connections must be tight
with no leakage.
Clean or replace any damaged or dirty air or water lines
which may be corroded, before connecting them to the
compressor. Use a new discharge fitting gasket.
Align compressor drive and adjust proper belt tension.
Tighten mounting bolts securely and evenly.
After installation, run compressor and check for air, oil, or
water leaks at compressor connections. Also check for
noisy operation.
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 filter 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.

Drain the engine cooling system and the cylinder head of
the compressor. Disconnect all air, water and oil lines leading
to and from the compressor. 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 fitted,
they must be replaced if they are worn or damaged.

DISASSEMBLY
GENERAL
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 both the front and rear end cover in relation to the
crankcase. Mark the drive end of the crankshaft in relation
to the front end cover and the crankcase. Mark the cylinder
head in relation to the block and block to 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 a marking method that can be wiped off or
obliterated during rebuilding, such as chalk. Remove all
compressor attachments such as governors, air strainers
or inlet fittings, discharge fittings and pipe plugs.
CYLINDER HEAD
Remove the cylinder head cap screws and tap the head
with a soft mallet to break the gasket seal. Remove the
inlet valve springs form the head and inlet valves from their
guides in the block. Remove inlet valve guides from around
the inlet valve seats on the block, taking care not to damage
seats. Scrape off any gasket material from the cylinder
head and block. Unscrew the discharge cap nuts from the
head and remove the discharge valves and springs. Inspect
the discharge valve seats for nicks, cracks, and excessive
wear and remove and replace if necessary.
The discharge valve cap nuts should be inspected for wear
and replaced if excessive peening has occurred. To
determine if excessive peening has occurred, measure the
discharge valve travel. Discharge valve travel must not exceed
.056 in. for the Tu-Flo® 400 compressor and .046 in. for the
Tu-Flo® 500 and 1000 compressors.

CRANKCASE BASE PLATE OR ADAPTER
Remove the cap screws securing the base plate or base
adapter. Tap with soft mallet to break the gasket seal. Scrape
off any gasket material from crankcase and plate or adapter.

REMOVING AND DISASSEMBLY

CONNECTING ROD ASSEMBLIES

REMOVING

(NOTE: Before removing the connecting rods, mark each
connecting rod and its cap. Each connecting rod
is matched to its own cap for proper bearing fit, and
these parts must not be interchanged.)

These instructions are general and are intended to be a
guide. In some cases additional preparations and
precautions are necessary. Chock the wheels of the vehicle
and drain the air pressure from all the reservoirs in the system.

7

FIGURE 17 - TU-FLO® 400 AIR COMPRESSOR VERTICAL MOUNT - ENGINE LUBRICATED

Straighten the prongs of the connecting rod bolt lock strap
and remove the bolts and bearing caps. Push the piston
with the connecting rods attached out the top of the cylinders
of the crankcase. Replace the bearing caps on their
respective connecting rods. Remove the piston rings from
the pistons. If the pistons are to be removed from the
connecting rods, remove the wrist pin lock wires or teflon
plugs and press the wrist pins from the pistons and
connecting rods.
If the pistons are removed from the rod, inspect the bronze
wrist pin bushing. Press out and replace the bushing if it is
excessively worn. (See Inspection of Parts.) Discard the
piston rings and the connecting rod journal bearings. Discard
the wrist pin bushings if they were removed. New Tu-Flo®
400 compressors manufactured after approximately
September 1977 will have connecting rods without bearing
inserts. Repair size rods will have inserts.
REMOVING AND DISASSEMBLING BASE PLATE
SELF-LUBRICATED TYPE COMPRESSORS (Fig. 18)
Remove screws that hold base plate. Remove base plate.
Remove oil relief valve set screw, then oil relief valve.
Remove oil strainer retaining ring and lift out oil strainer.
Unless it is necessary, the oil pump piston bushing should
not be removed. If necessary, remove the bushing set screw,
then bushing and shim.
8

FIGURE 18 - BASE PLATE SELF-LUBRICATED TYPE
COMPRESSOR

Remove cotter pin from oil rod cap nuts, remove nuts, oil
pump piston rod and cap.
CRANKCASE (Fig. 19)
Remove end cover with oil seal, remove end cover gasket.
Replace oil seal after cleaning end cover.
Remove cap screws that hold opposite end cover to
crankcase; remove end cover and its gasket. Some
compressors have crankcases that have a shoulder for
positioning the crankshaft. In these cases the crankshaft
must be removed through one particular end.

Press the crankshaft and ball bearings from the crankcase,
then press ball bearings from crankshaft. Many compressors
will have sleeve-type bearings in the crankcase or in the end
cover. If the clearance between crankshaft journal and
bearing exceeds .0065 in. the sleeve bearing should be
replaced with appropriate undersize.

CLEANING AND INSPECTION OF PARTS
CLEANING
All parts should be cleaned thoroughly in a good cleaning
solvent before inspection.
CYLINDER HEAD ASSEMBLY
Remove all carbon deposits from discharge cavities and all
rust and scale from cooling cavities of cylinder head body.
Scrape all foreign matter from body surfaces and use air
pressure to blow dirt particles from all cavities.
Discharge valves can be dressed by lapping them on a piece
of fine crocus cloth on a flat surface, provided they are not
excessively worn.

FIGURE 19 - CRANKCASE - TU-FLO® 400 & 500 AIR
COMPRESSORS

CYLINDER BLOCK
Clean carbon and dirt from inlet and unloader passages.
Use air pressure to blow carbon and dirt deposits from
unloader passages.
Inlet valves, as in the case of discharge valves, not worn
excessively, can be cleaned by lapping them on a piece of
fine crocus cloth on a flat surface.
OIL PASSAGE

FIGURE 19A - CRANKCASE - TU-FLO® 1000 AIR
COMPRESSOR

BLOCK (Fig. 20)
If compressor is fitted with an air strainer, inlet elbow or
governor, remove same.
Remove cap screws securing cylinder block to crankcase;
separate crankcase and cylinder block and scrape off gasket.
Remove unloader spring, spring saddle and spring seat from
cylinder block.
Remove unloader guides and plungers and, with the use of
shop air, blow unloader pistons out of cylinder block unloader
piston bores.
Remove inlet valve guides; inlet valve seats can be removed
but only if they are worn or damaged and are being replaced.
Unloader bore bushings should be inspected but not removed
unless they are damaged.

Clean thoroughly all oil passages through crankshaft,
connecting rods, crankcase, end covers and base plate. If
necessary, inspect passages with a wire and blow foreign
matter out with air pressure.
CRANKCASE - SELF-LUBRICATED TYPE
The breather should be thoroughly washed and cleaned.
The oil pump check valve in the base should be removed
and replaced. It is important when the oil pump check valve
is replaced that it be installed correctly with the ball stop pin
end pressed in first. When installed, the ball and its seat
should be visible from the crankcase base.

INSPECTION OF PARTS
CYLINDER HEAD BODY
Inspect cylinder head body for cracks or damage.
WATER-COO LED TYPE
Use air pressure to test water jackets of cylinder head and
block for leakage. Replace unit if leakage is found.
DISCHARGE VALVES AND SEATS
If discharge valves are worn and grooved where they contact
the seats, they should be replaced. If the discharge valve
seats are worn excessively so that there is no longer enough
metal left to reclaim them by lapping, the seats should be
replaced.
DISCHARGE VALVE SPRING AND CAP NUTS
Replace all used discharge valve springs and cap nuts.

FIGURE 20 - CYLINDER BLOCK - EXPLODED VIEW
9

CRANKCASE AND END COVERS
Check for cracks or broken lugs in crankcase and end covers.
Also check their oil passages to make sure they are open
and clean.
If an oil seal ring is used in the end cover, check fit of ring in
ring groove. There should be 0.008 in. to 0.015 in. clearance
at the gap when placed in the end bore of the crankshaft. If
the oil ring is worn thin or is damaged, it should be replaced.
Inspect oil ring groove in end cover; if groove is worn
excessively replace end cover or machine groove for next
oversize oil seal ring.
If the crankshaft main bearings are installed in the end cover,
check for excessive wear and flat spots and replace if
necessary.
CYLINDER BLOCK
Check for cracks or broken lugs on cylinder block. Also
check unloader bore bushings to be sure they are not worn,
rusted or damaged. If these bushings are to be replaced
they can be removed by running a 1/8 in. pipe thread tap
inside the bushing, then inserting a 1/8 in. pipe threaded rod
and pulling the bushing straight up and out. Do not use an
easy-out for removing these bushings.
INLET VALVES AND SEATS
If inlet valves are grooved or worn where they contact the
seat, they should be replaced. If the inlet valve seats are
worn or damaged so they cannot be reclaimed by facing,
they should be replaced.
CYLINDER BORES
Cylinder bores which are scored or out of round by more
than 0.002 in. or tapered more than 0.003 in. should be
rebored or honed oversize. Oversize pistons are available in
0.010, 0.020, and 0.030 oversizes.
Cylinder bores must be smooth, straight and round.

Clearance between cast iron pistons and cylinder bores
should be between 0.002 in. minimum and 0.004 in.
maximum (Fig. 21).
PISTONS
Check pistons for scores, cracks or enlarged ring grooves;
replace 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 clearance is between 0.002 in.
minimum and 0.004 in. maximum.
Check fit of wrist pins on pistons and connecting rod bushings.
Wrist pin should be a light press fit in pistons. If wrist pin is
loose fit, the pin, piston, or both should be replaced. Check
fit of wrist pin in connecting rod bushing by rocking the piston.
This clearance should not exceed 0.0015 in. Replace wrist
pin bushings if excessive clearance is found. Wrist pin
bushings should be reamed after being pressed into
connecting rods. Replace used wrist pin lock wires.
Tu-Flo® 400 compressors manufactured after September
1977 will have Teflon plugs in each end of the wrist pins
instead of the lock wire. The Teflon plugs (pc. no. 292392)
may be used instead of the lock wires on all compressors.
See Fig. 22.
PISTON RINGS
Check fit of piston rings in piston ring grooves. Check ring
gap with rings installed in cylinder bores. Refer to Fig. 24
for correct gap and groove clearance.
All rings must be located in their proper ring grooves as
shown. The rings can be identified by the width and should
be installed with the bevel or the pipmark (if any) toward the
top of the piston. This applies to cast iron pistons (only as
shown above).
Die cast pistons use five (5) narrow rings.
COMPRESSION
RINGS (2)

COMPRESSION
RINGS (2)

FIGURE 22 - TU-FLO® 400 AIR COMPRESSOR NEW STYLE

FIGURE 21 - MEASURING CYLINDER BORES

10

TU-FLO® 400 AIR COMPRESSOR
CORRECT GROOVE
CLEARANCE

Used unloader mechanism should be replaced by unloader
kits 265014 for Type Tu-Flo® 400 compressors and 265015
for Types Tu-Flo® 500 and 1000 compressors. The Tu-Flo®
1000 compressor requires two kits per compressor.

.0015”
.0030”

The new unloader pistons should be a loose sliding fit in the
unloader piston bores of the cylinder block.

CORRECT GAP
CLEARANCE WITH RING
IN CYLINDER

PARTS SPECIAL TO SELF-LUBRICATED
TYPE COMPRESSORS

.0035”
.014”
FIGURE 23 - TU-FLO® 400 AIR COMPRESSOR OLD STYLE
TU-FLO® 500 & 1000 AIR COMPRESSOR
CORRECT GROOVE
CLEARANCE
NARROW
WIDE
.0035”
.0035”

.002”
.004”

OIL PUMP SCREEN
Check oil pump screen to be sure it is clean and not
damaged; replace if damaged.
OIL PUMP PISTON AND BUSHING
Check fit of oil pump piston in base plate pump bushing. It
must be a medium sliding fit. If excessive clearance is
found, the oil rod and/or bushing must be replaced.
OIL PUMP RELIEF VALVE

CORRECT GAP
CLEARANCE WITH RING
IN CYLINDER
.0035”
.014”

UNLOADER MECHANISM

If the oil pump relief valve is defective, it should be replaced.
NARROW
WIDE

FIGURE 24 - PISTON RING POSITIONS - GAPS AND
GROOVE CLEARANCE

OIL PUMP CHECK VALVE
The check valve should be replaced. It can be checked by
applying air pressure back through the pin stop end and
noting that the ball check seals on its seat.

REPAIRS
CRANKSHAFT

DISCHARGE VALVES AND SEATS

Check crankshaft screw threads, keyways, tapered ends
and all machined and ground surfaces for wear, scores, or
damage. Crankshaft journals which are out of round more
than 0.001 in. must be reground. Bearing inserts are available
in 0.010 in., 0.020 in., and 0.030 in. undersizes for reground
crankshafts. Main bearing journals must be maintained so
bearings are snug fit. The oil seal ring groove or grooves in
crankshafts fitted with oil seal rings must not be worn. The
ring groove walls must have a good finish and they must be
square. Check to be sure the oil passages are open and
clean through the crankshaft.

If discharge valve seats merely show signs of slight wear,
they can be dressed by using a lapping stone, grinding
compound and grinding tool. Install new discharge valves
and valve springs.

CONNECTING ROD BEARINGS
Check connecting rod bearings on crankshaft journals for
proper fit. Used bearing inserts should be replaced.
Connecting rod caps are not interchangeable. The locking
slots of the connecting rod and cap should be positioned
adjacent to each other.
Clearance between the connecting rod journal and the
connecting rod bearing must not be less than 0.0003 in. or
more than 0.0021 in. after rebuilding.
MAIN BEARINGS
Check for wear or flat spots; if found, bearings should be
replaced. If type with sleeve bearing, this bearing should be
checked for scores and wear and replaced if necessary.

To test for leakage by the discharge valves, apply about 100
pounds of air pressure through the cylinder head discharge
port and apply soap suds at the discharge valves and seats.
Leakage which will permit the formation of bubbles is
permissible.
If excessive leakage is found, leave the air pressure applied,
and with the use of a fibre or hardwood dowel and hammer,
tap the discharge valves off their seats several times. This
will help the valves to seat and should reduce any leakage.
With the air pressure still applied at the discharge port of
the cylinder head, check for leakage at the discharge valve
cap nuts. No leakage is permissible.
INLET VALVES AND SEATS
If inlet valve seats show sign of slight nicks or scratches,
they can be redressed with a fine piece of emery cloth or by
lapping with a lapping stone, grinding compound and grinding
tool. If the seats are excessively damaged to the extent
that they cannot be reclaimed, they should be replaced.
The dimension from the top of the cylinder block to the inlet
valve seat should not exceed 0.118 in. nor be less than
0.101 in.
11

Slightly worn or scratched inlet valves can be reclaimed by
lapping them on a piece of fine crocus cloth on a flat surface,
but it is suggested that new inlet valves be installed.

ASSEMBLY
INSTALLING CYLINDER BLOCK
Position cylinder block gasket and block on crankcase
according to markings made prior to disassembly. Using
cap screws with lock washers, secure cylinder block to
crankcase.

Remove connecting bolts and bearing cap from one
connecting rod. Turn crankshaft so one of its connecting
rod journals is in the downward, center position. Compress
the rings with a ring compression tool and insert the
connecting rod with piston through the top of the cylinder
whose journal is down. Position and attach the bearing cap
to the connecting rod, making sure the bolt lock washers
are properly positioned on the cap. Tighten connecting rod
bolts evenly and bend the two new lock washer prongs up
against the hex head of the bolt. Install the other connecting
rod and piston in the same manner.

INSTALLING CRANKSHAFT
If the crankshaft is fitted with oil seal rings, install rings.
Position ball bearings and crankshaft in crankcase, making
sure the drive end of the crankshaft is positioned as marked
before disassembly.
If one end of the crankcase is counterbored for holding a
bearing, be sure the crankshaft is installed through the correct
end of the crankcase.
Carefully press crankshaft and bearings into crankcase using
arbor press.
Position a new rear end cover gasket, when used, over the
rear end of the crankcase, making sure the oil hole in the
gasket lines up with the oil hole in the crankcase. Position
end cover with oil seal ring, if used, installed over crankcase
and end cover gasket. The end cover should be positioned
correctly in relation to the oil holes in the gasket and
crankcase. Secure end cover to crankcase with cap screws
and lock washers.
If the opposite end cover requires an oil seal which was
removed on disassembly, a new seal should be pressed
into end cover. Position new end cover gasket and carefully
install end cover over crankshaft and to crankcase, avoiding
damage to the seal. Secure end cover with cap screw and
lock washers.
PISTONS AND CONNECTING RODS
If new wrist pin bushings are to be used, they should be
pressed into the connecting rods so that the oil hole in the
bushing lines up with the one in the rod. The new bushings
should then be reamed or honed to provide between 0.0002
in and 0.0007 in. clearance on the wrist pin. Position
connecting rod in piston and press in wrist pin so that
lockwire hole in the pin aligns with that of the piston. Install
new lockwire through piston and wrist pin and lock same by
snapping short end into lockwire hole at the bottom of the
piston (Fig. 7). Teflon plugs in wrist pin ends may be used
instead of the lockwires (Fig. 22).
Install piston rings in correct location with ring pipmarks up
(Fig. 24). Stagger the position of the ring gaps.
Prelubricate piston, piston rings, wrist pin and connecting
rod bearings with clean engine oil before installing them in
the compressor.
12

FIGURE 25 - UNLOADER MECHANISM

UNLOADER MECHANISM (Fig. 25)
The unloader pistons and their bores must be lubricated
with special lubricant piece number 239379 (dimethyl
polysiloxane) prior to installation. If new unloader kits are
being installed, the pistons in the kit are already lubricated.
Install the unloader pistons in their bores with caution against
cutting the grommets or distorting the back-up rings. Position
unloader plungers in their guides and slip them in and over
the tops of the pistons.
Install the unloader spring seat in the cylinder block; a small
hole is drilled in the block for this purpose. Position the
saddle between unloader piston guides so its forks are
centered on the guides. Install the unloader spring, making
sure it seats over the spring seats both in the block and on
the saddle.
Install inlet valve seats if they have been previously removed.
Position and install inlet valve guides, then drop inlet valves
in their guides. There should be a loose sliding fit between
guides and valves.
CYLINDER HEAD ASSEMBLY
If previously removed, the discharge valve seats should be
installed. Drop discharge valves into their seats. Install
discharge valve springs and cap nuts.
Place the inlet valve springs in the cylinder head. Use a
small quantity of grease to hold them in place, just enough
grease to keep the springs from falling out. Place cylinder
head gasket on cylinder block. Carefully align cylinder head
assembly on block and install cap screws with lock washers.
Tighten securely and evenly cap screws that hold cylinder
head to block.

BASEPLATE

TESTING REBUILT COMPRESSOR

SELF-LUBRICATED TYPE COMPRESSORS
Install oil pump piston and rod on crankshaft.

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.

Oil rod bearing fit must be the same as specified for
connecting rod bearings. Install oil rod cap nuts and cotter
pins to lock oil rod nuts.
Install oil pump relief valve in base plate. The relief valve can
be tested at this stage by applying air pressure to the relief
valve. The valve should open when the pressure is between
14 psi minimum and 24 psi maximum. When the relief valve
is properly installed in the base plate, install set screw that
locks it in place.
Place oil pump screen in base and install retaining ring,
making sure it snaps in place and secures the screw.
Install oil filter fitting on base plate in its proper place. Install
blanking cover on opposite oil filter fitting hole in plate.
Install a new oil seal gasket around oil pump - check valve
and position a new base plate gasket on the crankcase.
Position base plate assembly on crankcase, making sure
oil pump piston engages the oil pump bushing in the base
plate. Install and tighten base plate screws.

A compressor efficiency or build-up test can be run which is
not too difficult. Before the test, the crankcase of a selflubricated type compressor should be properly filled with
lubricating oil. An engine lubricated compressor must be
connected to an oil supply line of at least 15 pounds pressure
during the test and an oil return line must be installed to
keep the crankcase drained. The compressor (when tested)
should be tested without a strainer.
To the discharge port of the compressor, connect a reservoir
or reservoirs whose volume plus the volume of the connecting
line equals 1,300 cubic inches. Run the compressor between
1,700 and 1,750 RPM. Elapsed time that the compressor
takes to build up from 0 to 100 psi depends on the type
compressor as follows:
BUILD-UP TIME
TYPE COMPRESSOR
TU-FLO® 400
TU-FLO® 500
TU-FLO® 1000

0 TO 100 PSI
47 SECONDS MAXIMUM
30 SECONDS MAXIMUM
15 SECONDS MAXIMUM

During the above test the compressor should be checked
for oil leakage and noisy operation.

COMPRESSOR TROUBLESHOOTING
FIGURE 26 - AIR STRAINER - EXPLODED VIEW

AIR STRAINER
If the compressor is type with air strainer, assemble strainer
(Fig. 26). Using a new strainer gasket, install strainer on
cylinder block.

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.

GOVERNOR
If compressor is type with pad mounted governor, install a
new or factory rebuilt governor using a new governor gasket.
INSPECTION OF REBUILT UNIT
Check to be sure that covers, plugs or masking tape are
used to protect all ports if compressor is not to be installed
immediately.
Fit the end of all crankshafts with keys, nuts and cotter pins
as required and then protect the ends against damage by
wrapping with masking or friction tape.
The open bottom of engine lubricated compressors should
be protected against the entrance of dirt during handling or
storage, by installing a temporary cover over base.

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.
13

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 ADIS™ 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.

14

8. Use only genuine Bendix® replacement parts,
components and kits. Replacement hardware,
tubing, hose, fittings, etc. must be of equivalent
size, type and strength as original equipment and
be designed specifically 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 specifically 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.

MAINTENANCE INSTRUCTIONS FOR
LARGE SUMP TU-FLO® 1000 AIR
COMPRESSOR 288578 (SPECIAL
APPLICATION)
This compressor is an air-cooled, belt driven, self lubricated,
V-four cylinder compressor. It is driven by an electric motor
and cooling air is supplied by a fan on the driven pulley. The
system air pressure is controlled between 135 psi and 150
psi by a pressure switch starting and stopping the electric
motor.

INSTALLATION
The base mounted compressor should be securely bolted
down with 1/2" grade five or better cap screws torqued to 70
ft. pounds, making sure that motor and compressor pulleys
are aligned and belt tension is correct. The crankcase should
be filled with five quarts (4.7 liter) of SAE 20 W engine oil.
The compressor must always be installed to rotate clockwise
when viewed from the pulley end. The oil pump will not
function if rotation is not correct.

SCHEDULED MAINTENANCE
NOTE: When checking or adding oil or servicing the
crankcase breather, care should be taken to prevent
dirt or foreign material from entering the breather or
oil sump.
Every 7,500 miles or seven weeks, whichever occurs first:
Check oil level - replenish to top of filler plug opening.
Replace both air cleaner filter elements and clean covers.
Check belts and replace if broken, damaged or missing.
Every 15,000 miles or 14 weeks, whichever occurs first:
Remove crankcase ventilator, clean ports and replace with
freshly oiled curled hair.
Every 22,500 miles or 21 weeks, whichever occurs first:
Drain oil and refill with fresh SAE 20 W engine oil. Inspect
all bolts, fittings and plugs to ensure that all are tight.

TABULATED DATA

Number Cylinders
Bore Size
Stroke
Displacement at 1,250 RPM
Maximum recommended RPM
Minimum coolant flow at
maximum RPM
Approximate horsepower required
at 1,250 RPM
Maximum inlet air temperature
Maximum discharge air temperature
Minimum pressure required
to unload
Minimum oil pressure required at
engine idling speed
Minimum oil pressure required at
maximum governed engine speed
Approximate average weight
Oil capacity of self-lubricated model
Minimum discharge line size

Minimum coolant line size
Minimum oil supply line size
Minimum oil return line size
**Minimum air inlet line size

TU-FLO® 400
Air Compressor
2
2.0625"
1.5"
7.25 cu. ft./min.
3,000 water cooled
2,400 air cooled
2.5 gal./min.
water cooled
250 CFM air flow

TU-FLO® 500
Air Compressor
2
2.5"
1.6875"
12 cu. ft./min.
3,000 water cooled
2,400 air cooled
2.5 gal./min.
water cooled
250 CFM air flow

TU-FLO® 1000
Air Compressor
4
2.5"
1.6875"
24 cu. ft./min.
3,000 water cooled
2,400 air cooled
2.5 gal./ min.
water cooled
250 CFM air flow

1.2 H.P.
250° F.
400° F.

2.3 H.P.
250° F.
400° F.

4.6 H.P.
250° F.
400° F.

60 PSI

60 PSI

60 PSI

5 PSI

5 PSI

5 PSI

15 PSI
34 lbs.
.53 qts.
1/2" O.D. tubing
or equivalent

15 PSI
46 lbs.
.53 qts.
5/8" O.D. tubing
or equivalent

3/8" O.D. tubing
or equivalent
1/4" O.D. tubing
or equivalent
1/2" O.D. tubing
or equivalent
5/8" I.D.

1/2" O.D. tubing
or equivalent
1/4" O.D. tubing
or equivalent
5/8" O.D. tubing
or equivalent
5/8" I.D.

15 PSI
75 lbs.
.95 qts. to 5 qts.*
5/8" O.D. tubing or equivalent
from each head to a common
manifold with 1" tubing from
manifold.
1/2" O.D. tubing
or equivalent
1/4" O.D. tubing
or equivalent
5/8" O.D. tubing
or equivalent
1" I.D. if equipped with inlet
manifold; or, dual 5/8" I.D. lines
from engine to compressor inlets.

*Part Number dictates oil capacity
**Inlet line sizes specified for compressors with inlet connected to engine manifold.

15

This troubleshooting guide obsoletes and supersedes all previous published
troubleshooting information relative to Bendix air compressors.

Advanced Troubleshooting Guide
for Air Brake Compressors
*

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.

INDEX
Symptom

Page Number

Air

Symptom

Page Number

Coolant

Air brake charging system:
Slow build (9.0) . . . . . . . . . . . . . . . . . 24 - 25
Doesn’t build air (10.0) . . . . . . . . . . . . . . . 26
Air dryer:
Doesn’t purge (14.0) . . . . . . . . . . . . . . . . . 27
Safety valve releases air (12.0) . . . . . . . . . 27
Compressor:
Constantly cycles (15.0) . . . . . . . . . . . . . . 27
Leaks air (16.0) . . . . . . . . . . . . . . . . . . . . . 28
Safety valve releases air (11.0) . . . . . . . . . 26
Noisy (18.0) . . . . . . . . . . . . . . . . . . . . . . . . 28
Reservoir:
Safety valve releases air (13.0) . . . . . . . . . 27

Compressor leaks coolant (17.0) . . . . . . . . . . 28

Test Procedures

Maintenance & Usage Guidelines

(1) Oil Leakage at Head Gasket . . . 29
(2) System Leakage . . . . . . . . . . . . 29

Engine
Oil consumption (6.0) . . . . . . . . . . . . . . . . . . . 24
Oil
Oil Test Card results (1.0) . . . . . . . . . . . . . . . . 19
Oil is present:
On the outside of the compressor (2.0) . . . 20
At the air dryer purge/exhaust
or surrounding area (3.0) . . . . . . . . . . . 20
In the supply reservoir (4.0) . . . . . . . . 21 - 23
At the valves (5.0) . . . . . . . . . . . . . . . . . . . 23
At air dryer cartridge (7.0) . . . . . . . . . . . . . 24
In the ping tank or compressor
discharge aftercooler (8.0) . . . . . . . . . . 24

Maintenance Schedule and
Usage Guidelines (Table A) . . 18

(3) Compressor Discharge and
Air Dryer Inlet Temperature . . . . 29
(4) Governor Malfunction . . . . . . . . 30
(5) Governor Control Line . . . . . . . . 30
(6) Compressor Unloader . . . . . . . . 30
BASIC Test Information . . . . . . 32-34

*This guide is only for vehicles that use desiccant air dryers.
16

Introduction to the Air Brake Charging System
Powered by the vehicle engine, the air compressor
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 fittings, 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 18) 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 fitting
to avoid low points where ice may form and block the
flow. If, instead, ice blockages occur at the air dryer
inlet, insulation may be added here, or if the inlet fitting
is a typical 90 degree fitting, it may be changed to a
straight or 45 degree fitting. For more information on
how to help prevent discharge line freeze-ups, see
Bendix Bulletins TCH-08-21 and TCH-08-22 (see
pages 35-37). Shorter discharge line lengths or
insulation may be required in cold climates.
The air dryer contains a filter 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 filter, designed to minimize
the amount of oil present.

The Air Brake Charging System supplies the
Discharge
Line

Optional “Ping” Tank
Air Dryer

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.
Optional Bendix® PuraGuard®
System Filter or PuraGuard®
QC™ Oil Coalescing Filter

Compressor
Governor
(Governor plus Synchro valve
for the Bendix® DuraFlo™ 596™
Compressor)

Service Reservoir
(Supply Reservoir)

Reservoir Drain

17

Table A: Maintenance Schedule and Usage Guidelines
Regularly scheduled maintenance is the single most important factor in maintaining the air brake charging system.

Vehicle Used for:

No. of
Axles

Column 1

Column 2

Typical
Compressors
Spec'd

Discharge
Line
I.D.

Length

1/2 in.

6 ft.

Column 3
Recommended
Air Dryer
Cartridge
Replacement1

Column 4
Recommended
Reservoir
Drain
Schedule2

Column 5
Acceptable
Reservoir
Oil Contents3
at Regular
Drain Interval

e.g. Line haul single trailer
w/o air suspension, air over
hydraulic brakes.

5
or
less

e.g. Line haul single trailer
with air suspension,
school bus.

5
or
less

High 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, fire truck.

8
or
less

Compressor with up to 25% duty cycle

e.g. City transit bus, refuse,
bulk unloaders, low boys,
urban region coach, central
tire inflation.

12
or
less

Bendix® Tu-Flo® 750 air compressor

Compressor with up to 25% duty cycle

Bendix® BA-921™ air compressor

Compressor with up to 25% duty cycle

For oil carry-over
control4 suggested
upgrades:

5/8 in.

9 ft.
Every 3
Years

1/2 in.

9 ft.

For oil carry-over
control4 suggested
upgrades:

5/8 in.

1/2 in.

5/8 in.

12 ft.
Every 2
Years

15 ft.

Every
Month
5/8 in.

12 ft.

For oil carry-over
control4 suggested
upgrades:

3/4 in.

BASIC test
acceptable
range:
3 oil units
per month.
See
appendix
A.

For the
BASIC
Test Kit:
Order
Bendix
P/N
5013711

BASIC test
acceptable
range:
5 oil units
per month.
See
appendix
A.

Every
Year

15 ft.

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 sufficient 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 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.

18

Recommended
Every
Month Max of
every 90
days

12 ft.

For oil carry-over
control4 suggested
upgrades:
Bendix® BA-922™, or DuraFlo™ 596 air compressor

Compressor with less than 15% duty
cycle

Bendix® Tu-Flo® 550 air compressor

Low Air Use

Note: Compressor and/or air dryer
upgrades are recommended in cases
where duty cycle is greater than the
normal range (for the examples
above).
For Bendix® Tu-Flo® 550 and 750
compressors, unloader service is
recommended every 250,000 miles.

Air Brake Charging System Troubleshooting
How to use this guide:
Find the symptom(s) that you see, then move to the right to
find 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.

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.

Symptom:
1.0 Oil Test Card
Results

Look for:

Normal - Charging system is working within
normal range.

Check - Charging system needs further
investigation.

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, fittings, etc.
must be of equivalent size, type and strength as original
equipment and be designed specifically 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 specifically
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.

What it may indicate:

What you should do:

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
definitive method for judging excessive oil
fouling/oil passing. (See Appendix A, on
page 32 for a flowchart and expanded
explanation of the checklist used when
conducting the BASIC test.)

û
Bendix®
BASIC Test

ü

19

Symptom:

What it may indicate:

What you should do:

2.0 Oil on the
Outside of the
Compressor

Engine and/or other accessories
leaking onto compressor.

Find the source and repair. Return the vehicle
to service.

2.1 Oil leaking at
compressor / engine
connections:

(a)Leak at the front or rear (fuel
pump, etc.) mounting flange.

ð Repair or replace as necessary. If the
mounting bolt torques are low, replace the
gasket.

(b)Leak at air inlet fitting.

ð Replace the fitting gasket. Inspect inlet
hose and replace as necessary.

(c)Leak at air discharge fitting.

ð Replace gasket or fitting as necessary to
ensure good seal.

(d)Loose/broken oil line fittings.

ð Inspect and repair as necessary.

(a)Excessive leak at head gasket.

ð Go to Test 1 on page 29.

(b)Leak at bottom cover plate.

ð Reseal bottom cover plate using RTV
silicone sealant.

(c)Leak at internal rear flange gasket.

ð Replace compressor.

(d)Leak through crankcase.

ð Replace compressor.

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

ð Clean compressor and check periodically.

2.2 Oil leaking
from compressor:

ð

(c)

(a)

ð
(c)

3.0 Oil at air dryer
purge/exhaust or
surrounding area

20

Head
gasket
and rear
flange
gasket
locations.

Air brake charging system functioning
normally.

ð 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.

Symptom:

What it may indicate:

4.0 Oil in Supply or
Service Reservoir
(air dryer installed)

What you should do:

Maintenance

(a) If air brake charging system
maintenance has not been
(If a maintained Bendix
performed.
PuraGuard® system filter
That is, reservoir(s) have not been
or Bendix® PuraGuard®
drained per the schedule in Table
QC™ oil coalescing filter
is installed, call
A on page 18, Column 4 and/or the
1-800-AIR-BRAKE
air dryer maintenance has not
(1-800-247-2725) and
been performed as in Column 3.

ð Drain all air tanks and check vehicle at next
service interval using the Bendix® BASIC
test. See Table A on page 18, column 3
and 4, for recommended service schedule.

(b) If the vehicle maintenance has
been performed as recommended in Table A on page 18,
some oil in the reservoirs is normal.

ð 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
service. 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 29), 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.
ðIf within the normal range, return the
vehicle to service. For vehicles with
accessories that are sensitive to small
amounts of oil, consider a Bendix ®
PuraGuard® QC™ oil coalescing filter.
ð If outside the normal range go to
Symptom 4.0(c).
Also see the Table A on page 18, column
3 for recommended air dryer cartridge
replacement schedule.

®

speak to a Tech Team
member.)

(a)

See Table A, on page 18,
for maintenance
schedule information.
Drain all air tanks (reservoirs)
into the Bendix® BASIC test
cup. (Bendix kit P/N 5013711).

Duty cycle too high
(c) Air brake system leakage.

ð Go to Test 2 on page 29.

(d) Compressor may be undersized for
the application.

ð See Table A, column 1, on page 18 for
recommended compressor sizes.
ð If the compressor is "too small" for
the vehicle's role (for example, where a
vehicle's use has changed or service
conditions 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.
ð If the compressor is correct for the
vehicle, go to Symptom 4.0 (e).

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 fittings, connections, lines, chambers or valves, etc.

21

Symptom:

What it may indicate:

4.0 Oil in Supply
or Service
Reservoir*
(air dryer installed)
(continued)

What you should do:

Temperature
(e) Air compressor discharge and/or
air dryer inlet temperature too high.

ð Check temperature as outlined in Test 3
on page 29. If temperatures are normal
go to 4.0(h).

(f) Insufficient coolant flow.

ð Inspect coolant line. Replace as necessary
(I.D. is 1/2").
ð Inspect the coolant lines for kinks and
restrictions and fittings for restrictions.
Replace as necessary.

(f)

(e)

ð Verify coolant lines go from engine block
to compressor and back to the water pump.
Repair as necessary.

(g)

Testing the temperature
at the discharge fitting.

Inspecting the coolant hoses.

(g) Restricted discharge line.
(g)

ð 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 18 for recommended size. Replace
as necessary.
ð The discharge line must maintain a
constant slope down from the compressor
to the air dryer inlet fitting to avoid low
points where ice may form and block the
flow. If, instead, ice blockages occur at the
air dryer inlet, insulation may be added
here, or if the inlet fitting is a typical 90
degree fitting, it may be changed to a
straight or 45 degree fitting. 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.

Other
(h) Restricted air inlet (not enough air
to compressor).
(h)

Partly
collapsed
inlet line
shown.

ð Check compressor air inlet line for
restrictions, 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.
ð Check the engine air filter and service if
necessary (if possible, check the air filter
usage indicator).

*If a maintained Bendix® PuraGuard® system filter or Bendix® PuraGuard® QC™ oil coalescing
filter is installed, call 1-800-AIR-BRAKE (1-800-247-2725) and speak to a Tech Team
member.
22

Symptom:
4.0 Oil in Supply
or Service
Reservoir*
(air dryer installed)
(continued)

What it may indicate:

What you should do:

Other (cont.)
(i) Poorly filtered inlet air (poor air
quality to compressor).

Inspect the
engine air
cleaner.

ð Check for leaking, damaged or defective
compressor air inlet components (e.g.
induction line, fittings, gaskets, filter bodies,
etc.). Repair inlet components as needed.
Note: Dirt ingestion will damage
compressor and is not covered under
warranty.

(j) Governor malfunction or setting.

ð Go to Test 4 on page 30.

(k) Compressor malfunction.

ð If you found excessive oil present in the
service reservoir in step 4.0 (b) above and
you did not find 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 flushed from the air brake
system.

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.

*If a maintained Bendix® PuraGuard® system filter or Bendix® PuraGuard® QC™ oil coalescing
filter is installed, call 1-800-AIR-BRAKE (1-800-247-2725) and speak to a Tech Team
member.

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.

ð A small amount of oil does not affect SAE
J2024** compliant valves.
ð Check that regular maintenance is being
performed and that the amount of oil in the
air tanks (reservoirs) is within the
acceptable range shown on the Bendix®
BASIC test cup (see also column 5 of Table
A on page 18). Return the vehicle to
service.
For oil-sensitive systems, see page 17.
** SAE J2024 outlines tests all air brake system pneumatic
components need to be able to pass, including minimum
levels of tolerance to contamination.

Genuine
Bendix
valves are
all SAE
J2024
compliant.

23

Symptom:

What it may indicate:

What you should do:

6.0 Excessive oil
consumption in
engine.

A problem with engine or other engine
accessory.

ð See engine service manual.

7.0 Oil present at
air dryer cartridge
during
maintenance.

Air brake charging system is
functioning normally.

The engine
service
manual has
more
information.

Oil shown
leaking
from an air
dryer
cartridge.

24

ð 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 18). Replace the air
dryer cartridge as needed and return the
vehicle to service.

8.0 Oil in ping tank
or compressor discharge aftercooler.

Air brake charging system is
functioning normally.

ð Follow vehicle O.E. maintenance
recommendation for these components.

9.0 Air brake
charging system
seems slow to
build pressure.

(a) Air brake charging
functioning normally.

ð 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.

system

(b) Air brake system leakage.

ð Go to Test 2 on page 29.

(c) Compressor may be undersized for
the application.

ð See Table A, column 1, on page 18 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.

(d) Compressor unloader mechanism
malfunction.

ð Go to Test 6 on page 30.

(e) Damaged
gasket.

ð 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).

compressor

head

Symptom:
9.0 Air brake
charging system
seems slow to
build pressure.
(continued)

What it may indicate:

What you should do:

(f) Restricted discharge line.

ð If discharge line is restricted:
ð By more than 1/16" carbon build up,
replace the discharge line (see Table A,
column 2, on page 18 for recommended
size) and go to Test 3 on page 29.
ð By other restrictions (e.g. kinks).
Replace the discharge line. See Table A,
column 2, on page 18 for recommended
size. Retest for air build. Return vehicle to
service or, if problem persists, go to 9.0(a).

(f)

Dash gauges.

Kinked discharge line shown.

(g) Restricted air inlet (not enough air
to compressor).
(g)

ð The discharge line must maintain a
constant slope down from the compressor
to the air dryer inlet fitting to avoid low points
where ice may form and block the flow. If,
instead, ice blockages occur at the air dryer
inlet, insulation may be added here, or if
the inlet fitting is a typical 90 degree fitting,
it may be changed to a straight or 45 degree
fitting. 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.
ð Check compressor air inlet line for
restrictions, brittleness, soft or sagging
hose conditions etc. Repair as necessary.
Refer to vehicle manufacturer’s guidelines
for inlet line size.
ð Check the engine air filter and service if
necessary (if possible, check the air filter
usage indicator).

Partly collapsed
inlet line shown.

(h) Poorly filtered inlet air (poor air
quality to compressor).

ð Check for leaking, damaged or defective
compressor air inlet components (e.g.
induction line, fittings, gaskets, filter
bodies, etc.). Repair inlet components as
needed. Note: Dirt ingestion will damage
compressor and is not covered under
warranty.

(i) Compressor malfunction.

ð Replace the compressor only after making
certain that none of the preceding
conditions, 9.0 (a) through 9.0 (h), exist.

25

Symptom:
10.0 Air charging
system doesn’t
build air.

What it may indicate:
(a) Governor malfunction*.

ð Go to Test 4 on page 30.

(b) Restricted discharge line.

ð See 9.0(f).

(c) Air dryer heater malfunction:
exhaust port frozen open.

ð Replace air dryer heater.

(d) Compressor malfunction.

ð Replace the compressor only after making
certain the preceding conditions do not
exist.

* 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.

11.0 Compressor
safety valve
releases air
(Compressor
builds too much
air).

ð
26

What you should do:

(a) Restricted discharge line.

Damaged
discharge
line
shown.

ð If discharge line is restricted:
ð By more than 1/16" carbon build up,
replace the discharge line (see Table A,
column 2, on page 18 for recommended
size) and go to Test 3 on page 29.
ð By other restrictions (e.g. kinks).
Replace the discharge line. See Table A,
column 2, on page 18 for recommended
size.
ð The discharge line must maintain a
constant slope down from the compressor
to the air dryer inlet fitting to avoid low
points where ice may form and block the
flow. If, instead, ice blockages occur at the
air dryer inlet, insulation may be added
here, or if the inlet fitting is a typical 90
degree fitting, it may be changed to a
straight or 45 degree fitting. For more
information on how to help prevent discharge
line freeze-ups, see Bendix Bulletins TCH08-21 and TCH-08-22 (Appendix B).
Shorter discharge line lengths or insulation
may be required in cold climates.

(b) Downstream air brake system
check valves or lines may be
blocked or damaged.

ð Inspect air lines and verify check valves
are operating properly.

(c) Air dryer lines incorrectly installed.

ð Ensure discharge line is installed into the
inlet of the air dryer and delivery is routed
to the service reservoir.

(d) Compressor safety valve
malfunction.

ð Verify relief pressure is 250 psi. Replace
if defective.

(e) Compressor unloader mechanism
malfunction.

ð Go to Test 6 on page 30.

(f) Governor malfunction.

ð Go to Test 4 on page 30.

Symptom:
12.0 Air dryer
safety valve
releases air.

What it may indicate:

What you should do:

(a) Restriction between air dryer and
reservoir.

ð Inspect delivery lines to reservoir for
restrictions and repair as needed.

(b) Air dryer safety valve malfunction.

ð Verify relief pressure is at vehicle or
component manufacturer specifications.
Replace if defective.

(c) Air dryer
performed.

ð See Maintenance Schedule and Usage
Guidelines (Table A, column 3, on page
18).

Air dryer
safety valve

ð

maintenance

not

(d) Air dryer malfunction.

ð Verify operation of air dryer. Follow vehicle
O.E. maintenance recommendations and
component Service Data information.

(e) Improper governor control line
installation to the reservoir.

ð Go to Test 5 on page 30.

(f) Governor malfunction.

ð Go to Test 4 on page 30.

(a) Reservoir safety valve malfunction.

ð Verify relief pressure is at vehicle or
component manufacturer's specifications
(typically 150 psi). Replace if defective.

(b) Governor malfunction.

ð Go to Test 4 on page 30.

(c) Compressor unloader mechanism
malfunction.

ð Go to Test 6 on page 30.

(a) Air dryer malfunction.

ð Verify operation of air dryer. Follow vehicle
O.E. maintenance recommendations.

(b) Governor malfunction.

ð Go to Test 4 on page 30.

(c) Air brake system leakage.

ð Go to Test 2 on page 29.

(d) Improper governor control line
installation to the reservoir.

ð Go to Test 5 on page 30.

(a) Air brake charging system
maintenance not performed.

ð 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 18.

(b) Compressor unloader mechanism
malfunction.

ð Go to Test 6 on page 30.

(c) Air dryer purge valve or delivery
check valve malfunction.

ð Verify operation of air dryer. Follow vehicle
O.E. maintenance recommendations and
component Service Data information.

(d) Air brake system leakage.

ð Go to Test 2 on page 29.

ê
ê

Technician removes
governor.

13.0 Reservoir
safety valve
releases air

14.0 Air dryer
doesn’t purge.
(Never hear
exhaust from air
dryer.)

15.0 Compressor
constantly cycles
(compressor
remains unloaded
for a very short
time.)

27

Symptom:
16.0 Compressor
leaks air

What it may indicate:
(a) Compressor leaks
connections or ports.

at

ð Check for leaking, damaged or defective
compressor fittings, gaskets, etc. Repair
or replace as necessary.
ð Go to Test 6 on page 30.

(c) Damaged
gasket.

head

ð An air leak at the head gasket may indicate
a downstream restriction such as a freezeup 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).

(a) Improperly installed plugs or
coolant line fittings.

ð Inspect for loose or over-torqued fittings.
Reseal and tighten loose fittings and plugs
as necessary. If overtorqued fittings and
plugs have cracked ports in the head,
replace the compressor.

(b) Damaged
gasket.

head

ð An air leak at the head gasket may indicate
a downstream restriction such as a freezeup 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).

(c) Porous compressor head casting.

ð If casting porosity is detected, replace the
compressor.

(a) Damaged compressor.

ð Replace the compressor.

compressor

Head
gasket
location

ð

18.0 Noisy
compressor
(Multi-cylinder
compressors only)

air

(b) Compressor unloader mechanism
malfunction.

Testing for leaks
with soap solution.

17.0 Compressor
leaks coolant

What you should do:

compressor

Other Miscellaneous Areas to Consider
This guide attempts to cover most
compressor 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.

28

• 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
connecting rod bearings. Damage of this
kind may not be detected and could lead
to compressor problems at a later date.

Tests
Test 1: Excessive Oil Leakage at the
Head Gasket
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.

LOOK
FOR
WEEPAGE

Test 2: Air Brake System and Accessory Leakage
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

Test 3: Air Compressor Discharge
Temperature and Air Dryer Inlet
Temperature*
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
five (5) minutes.

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 confirm
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.

(* Note that only vehicles that have passed Test 2
would be candidates for this test.)
4. Then, while maintaining max rpm and
pressure range, measure and record the
surface temperature of the fittings:
ð at the compressor discharge port. (T1).
ð at the air dryer inlet fitting. (T2).
Use a touch probe thermocouple for
measuring the temperature.
5. See table below.
6. Retest before returning the vehicle to service.

T1

T2

Compressor Air Dryer
Discharge
Inlet
Fitting
Fitting

under
360°F

under
200°F

Temperatures are within
normal range for this test, check
other symptoms. Go to 4.0 (h).

under
360°F

over
200°F

This could indicate a discharge
line problem (e.g. restriction).
Call 1-800-AIR-BRAKE
(1-800-247-2725)
and speak with our Tech Team.

over
360°F

__

T1

T2

Discharge Line

Action

Compressor is running hot.
Check coolant 4(f) and/or
discharge line 4(g).

29

Tests (continued)
Test 4: Governor Malfunction
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 cutout pressures are within vehicle OEM
specification.
3. If the governor is malfunctioning, replace it.

Test 5: Governor Control Line
1. Ensure that the governor control line from the
reservoir is located at or near the top of the
reservoir. (This line, if located near the bottom
of the reservoir, can become blocked or
restricted by the reservoir contents e.g. water
or ice.)

2. Perform proper reservoir drain intervals and
air dryer cartridge maintenance per
Maintenance Schedule and Usage Guidelines
(Table A on page 18).
3. Return the vehicle to service.

Test 6: Compressor Unloader Leakage
Bendix ® Compressors: Park vehicle, chock
wheels, and follow all standard safety procedures.
Remove the governor and install a fitting to the
unloader port. Add a section of air hose (min 1ft
long for a 1/2" diameter line) and a gauge to the
fitting followed by a shut-off valve and an air
source (shop air or small air tank). Open the shut

30

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.

NOTES

31

Appendix A: Information about the BASIC Test Kit (Bendix P/N 5013711)
Service writer records info - including
the number of days since all air tanks
were drained - and fills out symptom
checklist. Technician inspects items.

days

Bendix® Air System Inspection Cup
(BASIC) Test Information

START BASIC TEST
Park vehicle on LEVEL ground.
Chock wheels, drain air from system.

Drain contents of ALL air
tanks into BASIC cup

Is there
less than one
unit of liquid?

Vehicle OK.
Return vehicle to
service.

YES

END TEST

NO
Is
there more
than one unit of:
• water, or
• cloudy emulsion
mixture?

Cloudy emulsion mixture

YES

NO, only oil.
Is this a
transit vehicle, bulk
unloader, or has more
than 5 axles?

YES, this is a high
air use
vehicle.

Hig

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.

h

Low

Hig

Is the
point above
the HIGH Air Use
line on the
cup?
H

NO, this is a low air
use vehicle.

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.

h

Is the
point above
the LOW Air Use
line on the
cup?

NO

YES

Test for air
leakage

Low

Does
the vehicle have
excessive air
leakage?

YES

Was
the number of
days since last
draining
known?

Change air dryer
cartridge**

Test for air
leakage

Use Test 2:
Air Leakage

Re-test with the
BASIC Test after
30 days***

END TEST

Repair leaks and
return vehicle to
service

END TEST

NO (did not know
when last
drained) Re-test with the
BASIC Test after
30 days***

END TEST

* 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.

END TEST

YES, number of days
was known (30 - 90 days)

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).

END TEST

NO

Low

Vehicle OK.
Return vehicle to
service.

NO

32

END TEST

YES

Use Test 2:
Air Leakage

Is this vehicle
being re-tested (after
water, etc. was found
last time?)

Go to the
Advanced
Troubleshooting
Guide to find
reason(s) for
presence of water

NO

igh

Compressor

YES

*** 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
on pages 35-37 of this document).
****Note: After replacing a compressor, residual oil may take a
considerable period of time to be flushed from the air brake system.

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

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.

The Service Writer fills out these fields with information gained from the customer
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: ____________________
Checklist for Technician

The Service Writer
also checks off any
complaints that the
customer makes to
help the Technician
in investigating.

Have you confirmed complaint?
è

Customer’s Complaint
(Please check all that apply)

“Relay valve q leaks oil / q malfunctions” . . . . . . . q no q yes*
“Dash valve q leaks oil / q malfunctions” . . . . . . . q no q yes*
q “Air dryer leaks oil” . . . . . . . . . . . . . . . . . . . . . . . q no q yes*
q “Governor malfunction” . . . . . . . . . . . . . . . . . . . . q no q yes*
q “Oil in gladhands” . . . . . . . . . . . . . . . . . . . . . . . . q no q yes*
how much oil did you find? ________________________________
q “Oil on ground or vehicle exterior” . . . . . . . . . . . q no q yes*
amount described: ______________________________________
q “Short air dryer cartridge life”
replaces every: ______________ q miles, q kms, or q months
q “Oil in air tanks” amount described:_______________________
We will measure amount currently found when we get to step B of the test.

q “Excessive engine oil loss” amount described: ______________
Is the engine leaking oil? . . . . . . . . . . . . . . . . . . . . . q no q yes*
Is the compressor leaking oil? . . . . . . . . . . . . . . . . . q no q yes*
q Other complaint:
______________________________________
q No customer complaint.

BASIC test starts here:

STEP A - Select one:

q This is a low air use vehicle: Line haul (single trailer) with 5 or less axles, or
q This is a high air use vehicle: Garbage truck, transit bus, bulk unloader, or
line haul with 6 or more axles.
Then go to Step B.

STEP B - Measure the Charging System Contents
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:
(a) Change the vehicle’s air dryer cartridge
Oil
- see Footnote 1,
Units
(b) Conduct the 4 minute leakage test (Step D),
(c) STOP the inspection, and check the vehicle
again after 30 days - see Footnote 2. STOP
Otherwise, go to Step C.

+ CK.

The Technician
checks boxes for
any of the
complaints that
can be confirmed.

* Note: A confirmed complaint above does NOT mean
that the compressor must be
replaced.
The full BASIC test below will
investigate the facts.

The Technician selects the air use
category for the vehicle. This
decided 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.
Note for returning vehicles that are being
retested 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.

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).
33

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

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.

2. Record amount
of oil found:

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).

_________ days

_________ units

3. Action to
take
è

è

1. Record days since air
tanks were last drained.

è

STEP C - How to Use the BASIC Test

if oil level is at or below System OK.
STOP
If number of days is:
acceptance line for number
TEST
30-60 days (high air
Return
to
service.
of daysè
use) or
if oil level is above
30-90 days (low air use)
Go to Step D
acceptance line for number
è
of days è
if oil level is at or below System OK.
STOP
TEST
30-day acceptance line è
Return to service.
Stop inspection.
(if the number of days is
STOP
unknown, or outside the if oil level is above 30-day Test again
acceptance
line
è
after 30 days. + CK.
limits above)
See Footnote 2.

Otherwise . . .
è

Acceptance
Lines

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.

Oil
Level

X
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 we go to the leakage test.

Sixty days since last air
tank draining

STEP D - Air Brake System Leakage Test
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 confirm 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.
If no air leakage was detected, and if you are conducting
this test after completing Step C, go to Step E.

STEP E - If no air leakage was detected in Step D
Replace the compressor.
Note: If the compressor is within warranty period,
please follow standard warranty procedures. Attach
the completed checklist to warranty claim.

34

Decision point

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, for 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).

Appendix B

Technical Bulletin
Bulletin No.: TCH-008-021

Subject:

Effective Date: 11/1/92

Page: 1 of 2

Air Brake System - Cold Weather Operation Tips

As the cold weather approaches, operators and fleets 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 significant 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 form 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
6.0-9.5 ft.
9.5-12 ft.

I.D. Min.
½ in.
½ in.

12-16 ft.

5/8 in.

Other Requirements
None
Last 3 feet, including fitting at the end of the
discharge line, must be insulated with ½ inch thick closed
cell polyethylene pipe insulation.
Last 3 feet, including fitting 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.

35

Appendix B: Continued
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
figures 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
AD-4™ Air Dryer
AD-2™ Air Dryer
AD-IP™ Air Dryer
AD-SP™ Air Dryer
Trailer System-Guard™ Air Dryer

36

Service Data Sheet SD-08-2412
Service Data Sheet SD-08-2407
Service Data Sheet SD-08-2403
Service Data Sheet SD-08-2414
Service Data Sheet SD-08-2415
Service Data Sheet SD-08-2416

Appendix B: Continued

Technical Bulletin
Bulletin No.: TCH-008-022

Subject: Additional

Effective Date: 1/1/1994

Page: 1 of 1

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 flame 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) fluids into air brake lines or hose couplings (“glad hands”). Some fluids
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.

37

38

39

40

BW1420 © 2004 Bendix Commercial Vehicle Systems LLC All rights reserved. 10/2004 Printed in U.S.A.



---

Source Exif Data:

File Type                       : PDF
File Type Extension             : pdf
MIME Type                       : application/pdf
PDF Version                     : 1.7
Linearized                      : No
Author                          : Provided By MANUALSLIB.COM - http://www.manualslib.com/
Create Date                     : 2012:10:04 11:58:00Z
Keywords                        : manuals, instruction manuals, user manuals, service manuals, user guides, pdf manuals, owners manuals, installation guides
Modify Date                     : 2014:12:07 11:52:57+08:00
Subject                         : Search through 700.000 manuals online & and download pdf manuals.
Has XFA                         : No
XMP Toolkit                     : Adobe XMP Core 5.4-c005 78.147326, 2012/08/23-13:03:03
Format                          : application/pdf
Creator                         : Provided By MANUALSLIB.COM - http://www.manualslib.com/
Description                     : Search through 700.000 manuals online & and download pdf manuals.
Title                           : ManualsLib - Makes it easy to find manuals online!
Creator Tool                    : pdftk 1.44 - www.pdftk.com
Metadata Date                   : 2014:12:07 11:52:57+08:00
Producer                        : itext-paulo-155 (itextpdf.sf.net-lowagie.com)
Document ID                     : uuid:be0d4468-0e1e-f54e-9d60-afcd8cb4bd25
Instance ID                     : uuid:9e165549-2268-6549-a9c4-a477d2dbac16
Page Count                      : 40

EXIF Metadata provided by EXIF.tools