BENDIX TU-FLO 501 AIR COMPRESSOR User manual

1
®
Bendix®TU-FLO®501 Air Compressor
SD-01-337
DESCRIPTIONAND OPERATION
General
Thefunctionoftheaircompressoristoprovideandmaintain
air under pressure to operate devices in the air brake and/
or auxiliary air systems.
Description
TheTu-Flo®501compressor isa two cylinder,singlestage,
reciprocating compressor with a rated displacement of 12
cubic feet of air per minute at 1250 R.P.M.
TheTu-Flo®501 compressoris constructed fromtwo major
assemblies,thehead andthecrankcase. Theheadhouses
thedischargevalvingandis installed ontheupperportion of
the crankcase. The crankcase is a one piece casting
combiningthecylinder blockand the crankcase.The upper
portion of the casting houses the cylinder bores and inlet
valving; and the lower portion, the crankshaft and main
bearings.Variousmountinganddriveconfigurations,required
by the numerous vehicle engine designs, are obtained by
bolting different mounting flanges, end covers, and base
adapterstothecrankcase.Twohorizontalgovernormounting
pads are located on either side of the upper portion of the
crankcasetoprovideconvenientgovernor mounting.
Two methods are employed for cooling the Tu-Flo®501
compressorduringoperation.Thecylinderheadisconnected
totheengine’scoolingsystem,whilethecylinderboreportion
of the crankcase has external fins for efficient air cooling.

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FIGURE 1 - VARIOUS COMPRESSOR MOUNTINGS
FIGURE2- COMPRESSOR NAMEPLATE
D-2 D-3D-1
AllTu-Flo®501compressorsutilizetheengine’spressurized
oilsystem to lubricatethe internal moving parts.
A nameplate is attached to the crankcase to identify the
compressor.ThenameplatedisplaysaBendixpiecenumber
orinsome cases anengineor vehiclemanufacturer’spiece
number, along with a serial number.
OPERATION
General
The compressor is driven by the vehicle engine and is
operating continuously while the engine is running. Actual
compressionof airiscontrolledbythecompressorunloading
mechanism and the governor. The governor is generally
mountedon thecompressorandmaintainsthebrakesystem
air pressure to a preset maximum and minimum pressure
level.
Intake and Compression of Air (Loaded)
During the down stroke of the piston, a slight vacuum is
createdbetweenthetop of thepistonandthehead, causing
theflat circularinlet valveto moveup andoff itsseat. (Note
the flat square discharge valve remains on its seat.)
Atmospheric air is drawn through the air strainer by the
open inlet valve and into the cylinder (see Fig. 4). As the
pistonbegins itsupward stroke, the air thatwas drawn into
the cylinder on the down stroke is being compressed. Air
pressureon top ofthe inletvalve plus theforce ofits spring,
returns the inlet valve to its seat. The piston continues the
upward stroke and compressed air then flows by the open
discharge valve, into the discharge line and on to the
reservoirs (see Fig. 5).As the piston reaches the top of its
stroke and starts down, the discharge valve spring and air
pressure in the discharge line returns the discharge valve
toitsseat.Thispreventsthe compressed air in the discharge
line from returning to the cylinder bore as the intake and
compression cycle is repeated.
Non-Compression of Air (Unloaded)
Whenairpressureinthereservoirreachesthecut-outsetting
of the governor, the governor allows air to pass from the
reservoirinto thecavity beneaththe unloaderpistons. This
liftsthe unloaderpistons andplungers. Theplungers move
up and hold the inlet valves off their seats (see Fig. 6).
With the inlet valves held off their seats by the unloader
pistonsandplungers,air is pumpedbackandforth between
the two cylinders. When air is used from the reservoir and
thepressure dropsto thecut-in settingof the governor,the
governor closes and exhausts the air from beneath the
unloader pistons. The unloader saddle spring forces the
saddle,pistonsandplungersdownandtheinletvalvesreturn
to their seats. Compression is then resumed.

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COMPRESSOR & THE AIR BRAKE SYSTEM
GENERAL
The compressor is part of the total air brake system, more
specifically,the chargingportion of theair brakesystem.As
acomponent inthe overallsystem itscondition, dutycycle,
proper installation and operation will directly affect other
components in the system.
Powered by the vehicle engine, the air compressor builds
theairpressurefortheairbrakesystem.Theaircompressor
istypically cooledby theengine coolantsystem, 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
enteringtheairsystem,themajority, butnotall,willcondense
in the reservoirs. The quantity of contaminants that reach
the air system depends on several factors including
installation,maintenanceandcontaminanthandlingdevices
inthe system.Thesecontaminantsmusteitherbeeliminated
prior to entering the air system or after they enter.
DUTYCYCLE
The duty cycle is the ratio of time the compressor spends
buildingairtothetotalenginerunning time.Aircompressors
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
undersizedcompressor,frequent stops, excessiveleakage
FIGURE 3A - SYSTEM DRAWING
AirDryer
Reservoir Drain
Service Reservoir
(Supply Reservoir)
Compressor
Governor
(Governor plus Synchro valve
for the Bendix®DuraFlo™596
Compressor)
Discharge
Line Optional“Ping” Tank
OptionalBendix®PuraGuard®QC™
OilCoalescing Filter
The Air Brake Charging System supplies the
compressedair for thebraking systemas well asother air
accessories for the vehicle. The system usually consists
of an air compressor, governor, discharge line, air dryer,
andservicereservoir.
from fittings, connections, lines, chambers or valves, etc.
RefertoTableAintheTroubleshootingsection foraguideto
variousdutycyclesandtheconsiderationthatmustbegiven
tomaintenance ofother components.
COMPRESSORINSTALLATION
While the original compressor installation is usually
completed by the vehicle manufacturer, conditions of
operation and maintenance may require additional
consideration.The following presentsbase guidelines.
DISCHARGELINE
Thedischarge line allowsthe air,water-vaporand oil-vapor
mixture to cool between the compressor and air dryer or
reservoir.The typical sizeof avehicle'sdischarge line,(see
column2ofTableAintheTroubleshootingsection)assumes
a compressor with a normal (less than 25%) duty cycle,
operating in a temperate climate. See Bendix and/or other
airdryermanufacturer guidelinesas needed.
The discharge line must maintain a constant slope down
fromthe compressorto theair dryer inlet fitting orreservoir
toavoidlowpointswhereicemayform and blocktheflow.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
45degreefitting.Shorterdischargelinelengthsor insulation
may be required in cold climates.
While not all compressors and charging systems are
equippedwith a dischargeline safetyvalve thiscomponent
isrecommended.Thedischargelinesafetyvalveisinstalled
in the cylinder head (Tu-Flo®550/750) or close to the
compressor discharge port and protects against over
pressurizingthecompressor in theeventof a dischargeline
freezeup.

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DISCHARGE
VALVE
PISTON
STROKE TO GOVERNOR
INTAKE
STRAINER
UNLOADER
PLUNGER
INLETVALVE
TO RESERVOIR
DISCHARGE
VALVE
PISTON
STROKE TO GOVERNOR
INTAKE
STRAINER
UNLOADER
PLUNGER
INLETVALVE
TO RESERVOIR
FIGURE 4 - INTAKE
FIGURE 5 - COMPRESSION
DISCHARGELINE TEMPERATURE
When the temperature of the compressed air that enters
the air dryer is within the normal range, the air dryer can
removemost of the charging systemoil. If the temperature
ofthe compressed airis 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
dischargeline lengthscan helpreduce thetemperature.
Theairdryer containsa filter thatcollects oildroplets,and a
desiccantbedthat removes almost alloftheremainingwater
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™oilcoalescing filter, designedto minimize
the amount of oil present.
Lubrication
Since all Tu-Flo®501 compressors are connected to the
engine’s pressurized oil system, a continuous flow of oil is
providedto the compressor,which is eventuallyreturned to
theengine.
Oilis fedinto thecompressor in various ways, for example:
throughtherearendcover,thedriveendofthecrankshaftor
through the front flange adapter. An oil passage in the
crankshaftconducts pressurizedoil tothe precisionsleeve
main bearings and to the connecting rod bearings. Splash
lubrication of the cylinder bores, connecting rod wrist pin
bushings,andtheballtypemainbearings,on some models,
isobtainedasoilisforcedoutaroundthecrankshaftjournals
byengine oilpressure.
Checktheexterior ofthe compressor forthe presenceofoil
seepageandrefer totheTROUBLESHOOTING section for
appropriatetests andcorrective action.
Cooling
Airflowingthrough theenginecompartment from theaction
ofthe engine’s fanand themovement of thevehicle assists
incooling the crankcase.Coolant flowingfrom theengine’s
cooling system through connecting lines enters the head
andpassesthrough the head’swater jacket andbackto the
engine.Propercoolingisimportantinmaintainingdischarge
airtemperaturesbelowthemaximum400°Frecommended.
FIGURE 3B - DISCHARGE LINE SAFETY VALVE
HOLE
THREAD
DISCHARGE
VALVE
PISTON
STROKE TO GOVERNOR
INTAKE
STRAINER
UNLOADER
PLUNGER
TO RESERVOIR
INLET VALVE
FIGURE 6 - UNLOADING

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PREVENTIVE MAINTENANCE
Regularly scheduled maintenance is the single most
importantfactorinmaintainingtheairbrakechargingsystem.
RefertoTableAintheTroubleshootingsection foraguideto
variousconsiderationsthatmustbegiventothemaintenance
of the compressor and other related charging system
components.
Everymonth,300operatinghoursoraftereach10,000miles,
dependingon the operatingconditions, experienceand the
typeof strainer used, service theair strainer.
POLYURETHANE SPONGE STRAINER EVERY
5000 MILES OR 150 OPERATING HOURS
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
andwatersolution.Theelementshouldbesaturatedinclean
engine oil, then squeezed dry before replacing it in the
strainer. Be sure to replace the air strainer gasket if the
entireair straineris removedfrom the compressor intake.
DRY ELEMENT-PLEATED PAPER AIR
STRAINER
EVERY 20,000 MILES OR 800 OPERATING HOURS
Removethe springclips from either side ofmounting baffle
andremove thecover.Replace thepleated paperfilterand
remount the cleaned cover making sure the filter is in
position. Be sure to replace the air strainer gasket if the
entireair straineris removedfrom the compressor intake.
(NOTE: Some compressors are fitted with compressor
intakeadapterswhich allowthe 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 compressorintakeadaptershouldbechecked.
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
bothat the compressorintake adapterand at theengine air
cleaner.Inspect the connectinglineforrupturesand replace
it if necessary.
EVERY 6 MONTHS, 1800 OPERATING HOURS
OR AFTER EACH 50,000 MILES
Remove the discharge head fittings and inspect the
compressordischargeportand discharge lineforexcessive
carbondeposits. If excessive buildup is noted ineither, the
discharge line must be cleaned or replaced and the
compressor checked more thoroughly, paying special
attention to the air induction system, oil supply and return
system, and proper cooling. If necessary, repair or replace
thecompressor.Checkfor proper beltand pulley alignment
and belt tension. Adjust if necessary, paying special
attentionnottoovertighten thebelttension.Checkfor noisy
compressor operation, which could indicate a worn drive
gear coupling or a loose pulley. Adjust and/or replace as
necessary. Check all compressor mounting bolts and
retightenevenlyif necessary.Checkforleakage and proper
unloadermechanism operation. Replace if defectivein any
way.
FIGURE 7 - POLYURETHANE SPONGE STRAINER
FIGURE8-PAPERAIR STRAINERDRYELEMENT-PLEATED
FIGURE9- COMPRESSOR INTAKEADAPTER

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EVERY 24 MONTHS, 7200 OPERATING HOURS
OR AFTER EACH 200,000 MILES
Perform a thorough inspection as indicated below and
dependingupontheresults of thisinspectionorexperience,
disassemble the compressor, clean and inspect all parts
thoroughly, repair or replace all worn or damaged parts
using only genuine Bendix replacements or replace the
compressor with a genuine Bendix remanufactured unit.
IMPORTANT - Should it be necessary to drain the engine
coolingsystemtopreventdamagefromfreezing,thecylinder
headof the compressor must also be drained.
GENERAL SERVICE CHECKS
Inspection
Itis ofthe utmostimportance thatthe compressor receives
a clean supply of air. The air strainer must be properly
installedandkeptclean.Ifthecompressorintakeisconnected
to the engine air cleaner, supercharger, etc., these
connections must be properly installed and maintained.
Checkthecompressormountingstobesuretheyaresecure.
Checkthe drivefor proper alignment, belt tension,etc.
Inspect the oil supply and return lines. Be sure these lines
are properly installed and that the compressor is getting
theproper supplyof oil, and just asimportant, thatthe oil is
returningto the engine.Check thecoolant lines toand from
the compressor and see that the cooling fins on the
crankcase are not clogged with dirt, grease, etc. Check
the unloader mechanism for proper and prompt operation.
Operating Tests
Vehicles manufactured after the effective date of FMVSS
121,withthe minimum required reservoirvolume,musthave
a compressor capable of raising air system pressure from
85-100 P.S.I. in 25 seconds or less. This test is performed
with the engine operating at maximum governed speed.
Thevehicle manufacturermust certifythis performance on
new vehicles with appropriate allowances for air systems
withgreaterthan the minimumrequired reservoir volume.
Air Leakage Tests
Leakage past the discharge valves can be detected by
removingthedischargeline, applying shopairbackthrough
the discharge port and listening for escaping air.Also, the
dischargevalves andthe unloaderpistons can be checked
forleakage by building up theair system until the governor
cutsout,thenstoppingtheengine.With the enginestopped,
listenfor escapingair atthe compressorintake.Topinpoint
leakage if noted, apply a small quantity of oil around the
unloader pistons. If there is no noticeable leakage at the
unloader pistons, the discharge valves may be leaking. If
the compressor does not function as described above, or
leakageis excessive,it isrecommended thatit bereturned
to the nearest authorized Bendix Distributor for a factory
remanufactured compressor. If this is not possible, the
compressor can be repaired using genuine Bendix
replacementparts, inwhich case,the following information
shouldprovehelpful.
REMOVINGAND DISASSEMBLY
Removing
These instructions are general and are intended to be a
guide, in some cases additional preparations and
precautionsarenecessary.Chockthe wheels ofthevehicle
and drain the air pressure from all the reservoirs in the
system. Drain the engine cooling system and the cylinder
head of the compressor. Disconnect all air, water and oil
linesleadingtoand fromthecompressor.Remove thedrive
gear(s) or pulley from the compressor crankshaft using a
gearpuller.Inspect the pulley or gear and associatedparts
forvisible wearor damage.Since theseparts areprecision
fitted, they must be replaced if they are worn or damaged.
DISASSEMBLY
General
Remove road dirt and grease from the exterior of the
compressorwitha cleaning solvent.Beforethe compressor
is disassembled, the following items should be marked to
showtheirrelationship when thecompressor is assembled.
Mark both the front and rear end cover in relation to the
crankcase. Mark the drive end of the crankshaft in relation
tothe frontend coverand thecrankcase. Markthe cylinder
head in relation to the crankcase. Mark the base plate or
base adapter in relation to the crankcase.
FIGURE 10 - TU-FLO®501AIR COMPRESSOR (THRU
DRIVE)EXPLODED VIEW

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Aconvenientmethod to indicatetheabove relationship isto
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
Removethe six cylinderhead capscrews andtap the head
withasoft mallettobreak thegasket seal. Removethe inlet
valvespringsfromtheheadandinletvalvesfromtheirguides
in the crankcase. Remove inlet valve guides from around
the inlet valve seats on the crankcase taking care not to
damage seats. Scrape off any gasket material from the
cylinderheadand crankcase.Unscrew the dischargevalve
seats from the head and remove the discharge valves and
springs.Inspectthe discharge valveseats for nicks,cracks,
and excessive wear and replace if necessary.
The discharge valve stops should be inspected for wear
and replaced if excessive peening has occurred. To
determineif excessivepeening has occurred, measure the
dischargevalvetravel.Dischargevalvetravelmustnotexceed
.057inches.Toremove thedischarge valve stops, support
themachinedsurfaceofthecylinderhead on anarborpress
bedandgently pressthestops fromthe top ofthe head and
outthe bottom.Be sureto allow sufficient clearance for the
stopsbetween the pressbed andthe bottom ofthe cylinder
head. The valve stop bores in the cylinder head must be
inspectedfor excessivescoring.Anewhead body must be
used if scoring is excessive. Discard the inlet valves and
springs,thedischargevalvesandspringsandthe discharge
valveseatsifdefective.
Crankcase Base Plate or Adapter
Remove the cap screws securing the base plate or base
adapter.Tapwithsoftmallettobreak the gasket seal. Scrape
offany gasket materialfromcrankcaseandplateor adapter.
Connecting Rod Assemblies
(Note: Before removing the connecting rods, mark each
connectingrod andits cap. Each connecting rod is
matched to its own cap for proper bearing fit, and
these parts must not be interchanged.)
Straighten the prongs of the connecting rod bolt lock strap
and remove the bolts and bearing caps. Push the piston
withtheconnectingrodsattachedoutthetopofthecylinders
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
connectingrods.
Ifthe pistonsare 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.
Crankcase
Removethe keyor keys from the crankshaftand any burrs
fromthe crankshaftwhere the key or keys were removed.
(Note: ThroughDriveCompressorsmayhaveacrankshaft
key at both ends.)
Removethefourcapscrewssecuring front ordrive-endend
coverorflange adapter.Removethe endcover,takingcare
notto damagethe crankshaft oil seal or front mainbearing,
if any. Remove both of the small seal rings from the
crankcase,and the o-ring from around the frontend cover.
Remove the four cap screws securing the rear end cover
and remove the rear end cover taking care not to damage
therearmain bearing,if any.Removeboth of thesmall seal
ringsfromthecrankcaseandtheo-ring from aroundtheend
cover.Ifthe compressorhas ball typemain bearings,press
the crankshaft and ball bearings from the crankcase, then
press the ball bearings from the crankshaft. Remove the
unloader spring, spring saddle, and spring seat from the
inletcavityofthecrankcase,usinglongnosepliers.Remove
theunloaderplungersandguides.Covertheinletcavitywith
ashoprag andapply air pressureto the governormounting
pad unloader port to blow the unloader pistons out of their
bores and into the inlet cavity.
CLEANING OF PARTS
General
All parts should be cleaned in a good commercial grade
solvent and dried prior to inspection.
Cylinder Head
Removeallthe carbondepositsfrom thedischarge cavities
and all the rust and scale from the cooling cavities of the
cylinder head body. Scrape all the foreign matter from the
body surfaces and use shop air pressure to blow the dirt
particles from all the cavities.
Crankcase
Clean the carbon and dirt from the inlet and unloader
passages. Use shop air pressure to blow the carbon and
dirtdeposits from theunloader passages.
Oil Passages
Thoroughly clean all oil passages through the crankshaft,
crankcase, end covers, and base plate or base adapter.
Inspect the passages with a wire to be sure. Blow the
loosenedforeign matterout withair pressure.

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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.
ForparticularlyoilsensitivesystemstheBendix®PuraGuard®
QC™oil coalescing filter can be used in conjunction with a
Bendixair 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"orBASIC testtohelpsubstantiatesuspectedexcessive
oilpassing.The steps tobe followed whenusingthe BASIC
test are presented in APPENDIX A at the end of the
TROUBLESHOOTINGsection.
INSPECTION OF PARTS
Cylinder Head Body
Inspectthecylinder headfor cracks ordamage.Applyshop
air pressure to one of the coolant ports with all others
plugged,andcheck forleakage by applyinga soap solution
to the exterior of the body. If leakage is detected, replace
thehead.
EndCovers
Check for cracks and external damage. If the crankshaft
main bearings are installed in the end cover, check for
excessivewearandflat spotsandreplacethemifnecessary.
Ifthe compressor hasan oil sealin the endcover, it should
beremoved bypressing it out of theend cover.
Crankcase
Check all crankcase surfaces for cracks and damage. On
compressorswhereballbearingmainbearingsareusedthe
differencebetweentheO.D. oftheouterrace andtheI.D.of
the crankcase hole should be .0000 in. to .0015 in. loose.
Thisisto maintainthecorrect press fit.The crankcase must
be replaced if the fit is too loose.
Oncompressorsfittedwithprecision, sleeve mainbearings,
the difference between the O.D. of the crankshaft journal
and the main bearing I.D. must not exceed .0065 in. If the
clearance is greater than .0065 in., the end cover or main
bearingmust be replaced.
Check the 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 into the bushing, and inserting a 1/8 in. pipe
threaded rod and pulling the bushing straight up and out.
Donot usean easy-out for removing thesebushings. If the
inlet valve seats are worn or damaged, so they cannot be
reclaimed by facing, they should be replaced. Cylinder
bores should be checked with inside micrometers or
calipers.(Fig.11).Cylinder boreswhich are scoredorout of
round by more than .001 in. or tapered more than .002 in.
shouldbereboredorhonedoversize.Oversizedpistonsand
piston rings are available in .010 in., .020 in. and .030 in.
oversizes. Cylinder bores must be smooth, straight, and
round.Clearancebetweenthecastironpistonsand cylinder
bores should be between .002 in. minimum and .004 in.
maximum.
FIGURE 11 - MEASURING CYLINDER BORES
FIGURE 12 - CORRECT GROOVE CLEARANCE
PISTON RING OIL RING
.001”
.003”
.002”
.004”
CORRECT GAP CLEARANCE
WITH RINGS IN CYLINDER
.002”
.010”
EXPANDER RING
OIL RING
PISTON RING
Pistons
Check the pistons for scores, cracks, or enlarged ring
grooves; replace the pistons if any of these conditions are
found. Measure each piston with a micrometer in relation
to the cylinder bore diameter to be sure the diametral
clearance is between .002 in. minimum and .004 in.
maximum.
Checkthe fitof the wrist pins to the pistonsand connecting
rodbushings. The wrist pin should be alight press fitin the
piston. If the wrist pin is a loose fit, the piston and pin
assembly should be replaced. Check the fit of the wrist pin
in the connecting rod bushing by rocking the piston. This
clearanceshouldnot exceed .0007in.Replace the wristpin
bushingsifexcessiveclearanceisfound.Wrist pin bushings
should be reamed to between .5314 in. and .5317 in. after
beingpressed into the connecting rods.
Check the fit of the piston rings in the piston ring grooves.
Check the ring gap with the rings installed in the cylinder
bores.RefertoFig.12forcorrectgapandgrooveclearances.

9
Crankshaft
Checkthe crankshaftthreads, keyways, taperedends and
all machined and ground surfaces for wear, scores, or
damage. Standard crankshaft journals are 1.1250 in. to
1.1242 in. in diameter. If the crankshaft journals are
excessively scored or worn or out of round and cannot be
reground, the crankshaft must be replaced. Connecting
rod bearing inserts are available in .010 in., .020 in. and
.030 in. undersizes for compressors with reground
crankshafts. Main bearing journals must be maintained so
theballbearingsare a snugfitorso that nomorethan.0065
in. clearance exists between the precision sleeve main
bearingand the mainbearing journalson thecrankshaft. In
crankshaftsfitted withoil sealrings, theoil sealring groove
or grooves must not be worn. The ring groove walls must
have a good finish and they must be square. Check to be
surethe oil passages are openthrough the crankshaft.
Connecting Rod Bearings
Used bearing inserts must be replaced. Connecting rod
caps are not interchangeable. The locking slots of the
connecting rod and cap should be positioned adjacent to
eachother.Clearance betweenthe connectingjournal and
the connecting rod bearing must not be less than .0003 in.
or more than .0021 in. after rebuilding.
REPAIRS
Discharge Valves, Valve Stops and Seats
Ifthedischargevalve seatsmerelyshowsignsofslightwear,
they can be dressed by using a lapping stone, grinding
compound and grinding tool. If the discharge valve stops
are to be replaced, an application of a sealer is required,
such as “Locktite Retaining Compound #75.” Be sure that
the press fit between the discharge valve stop outside
diameter and the valve stop bore in the cylinder head is a
minimum of .0008 in. and a maximum of .0028 in. If this fit
can not be maintained, a new cylinder head body must be
used. Be sure to completely support the outside top of the
cylinder head casting, while pressing in the replacement
stops. Install the new discharge valve springs and valves.
Screwin the discharge valve seats.Discharge valve travel
should be between .041 in. to .057 in.
Totestforleakagebythedischargevalves,apply100pounds
of air pressure through the cylinder head discharge port
andapplyasoapsolutiontothedischarge valves and seats.
Aslight leakagein theform of soap bubbles is permissible.
Ifexcessiveleakageis found,leavetheair pressure applied
andwiththe useofafibreorhardwooddowelandahammer,
tap the discharge valves off their seats several times. This
will help the valves to seat and should reduce the leakage.
With the air pressure still applied at the discharge port of
the cylinder head, check for leakage around the discharge
valvestopsexposedon thetopofthe cylinder headcasting.
Noleakage is permitted.
Inlet Valves and Seats
Inletvalvesandspringsshould bereplaced,iftheinlet valve
seats show signs of slight nicks or scratches. They can be
redressedwitha fine pieceofemery clothorby lapping with
alappingstone, grindingcompoundand grindingtool.If the
seats are damaged to the extent that they cannot be
reclaimed,they must be replaced. Thedimension from the
top of the cylinder block to the inlet valve seat should not
exceed .113 in. nor be less than .101 in.
ASSEMBLY
General Note: All torques specified in this manual are
assembly torques and can be expected to fall off after
assembly is accomplished. Do not retorque after initial
assemblytorques fall.
To convert inch pounds of torque to foot pounds of torque,
divideinch poundsby 12.
inch pounds ÷ 12 = foot pounds
To convert foot pounds of torque to inch pounds of torque,
multiply foot pounds by 12.
foot pounds x 12 = inch pounds
Installing the Crankshaft
Cautionary Note:
Allflangemountedcompressors must be assembledwithout
a gasket between the crankcase and flange adapter and
somecompressorsdonotrequiregasketsontheendcover.
Install the new crankcase gaskets only where they were
removed during disassembly. In service failure of the
compressor will occur if gaskets are used in disregard of
thepreceding.
FIGURE 13 - DISCHARGE
VALVE, VALVE STOPAND
SEAT
FIGURE 14 - INLET VALVE
ANDSEAT

10
If the compressor uses a ball type main bearing, press the
ballbearing onto thecorrect endof thecrankshaft. Position
theballbearingandthecrankshaftinthecrankcase, making
sure the drive end of the crankshaft is positioned in the
crankcase as marked before disassembly. Carefully press
thecrankshaft and ballbearing intothe crankcaseusing an
arborpress.
In the case of compressors with a front ball bearing, place
twosmall seal ringsin thecounter-sunkholes atthe front of
the crankcase, as well as an end cover gasket. Install the
front end cover in the proper position as marked before
disassembly, taking care not to damage the new oil seal.
In the case of compressors with a rear ball bearing, place
two small seal rings in the counter-bore at the rear of the
crankcase. In one case a gasket is used and in another a
large o-ring is placed in the counterbore at the rear of the
crankcase. These are in addition to the seal rings. Install
the rear end cover in the proper position as marked before
disassembly. Since June, 1978, the two small seal rings
havebeenincreasedslightlyincrosssectionand a retaining
ringadded, as shownin Figure 15.
Secure the flange adapter, front or rear end cover to the
crankcasebytightening thefourcapscrews.Seenotebelow
fortorque.
Note:For cast iron flange adapters, torque the four 7/16
in. cap screws to 38-45 foot pounds. For die cast
aluminum end covers, torque the four 7/16 in. cap
screws to 25-30 foot pounds.All end covers using
5/16 in. cap screws or stud and nuts are torqued
to15-18foot pounds.For through drivecompressors
with a cast iron end cover, torque the four 7/16 in.
cap screws to 25-30 foot pounds.
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
bushinglines upwith the onein therod. The new bushings
shouldthen bereamed orhoned toprovide between.0001
in. (.00254 mm) and .0006 in. (.01524 mm) clearance on
the wrist pin. Position the connecting rod in the piston and
press in the wrist pin.
Pistons installed in compressors manufactured prior to
November,1976, will have the wrist pinsecuredinthepiston
byalock wireextendingthrough matchingholesin wristpin
and piston boss, anchored in a hole in the side wall of the
piston.If the original pistons areused thewrist pin must be
pressedin so the hole inthe wrist pin aligns withthat of the
piston and secure same by inserting the new lockwire
throughthe holein pistonand wristpin andlock thewire by
snapping the short 90° section into the lockwire hole in the
bottom of the piston.
CompressorsbuiltafterNovember,1976,will havethewrist
pin secured by Teflon buttons in either end of the wrist pin,
allowing the wrist pin to float. The Teflon buttons pc. no.
292392 may be used with either new or old wrist pins. The
laterdesign pistons have two rings above the wristpin and
one below. Install the piston rings in the correct location
with the ring pipmarks up. Stagger the position of the ring
gaps. Pre-lubricate the piston, piston rings, wrist pins and
connectingrod.
Unloader
A new unloader kit should used when rebuilding. (Figure
14).(PieceNumber279615).The unloaderpistonsinthekit
are pre-lubricated with a special lubricant piece number
239379andneednoadditionallubrication.Installtheunloader
pistons in their bores being careful not to cut the o-rings.
Positiontheunloader plungersin their guidesand slip them
inandoverthetopsofthepistons.Installtheunloaderspring
seat in the crankcase inlet cavity; a small hole is drilled in
thecrankcaseforthispurpose. Position thesaddlebetween
theunloader pistonguides, soits forks are centered on the
guides. Install the unloader spring, making sure it seats
overthespringseatsbothinthecrankcaseandonthesaddle.
FIGURE 15
SEAL RING
SEAL RING
O-RING RETAINER
OLD
NEW
Inthecaseofcompressorswithasleeve bearing eitherfront
or rear, place the two small seal rings in the counter-sunk
holesinthecrankcase. Caution: Anend covergasketmust
notbe used.Place the o-ringseal inthe groove around the
flangeadapteror theendcover, andaffixthethrustwasher.
Installtheflange adapterorend cover inthe proper position
as marked before disassembly, taking care not to damage
thesleevebearing.

11
Positionandinstall the inletvalveguides, then droptheinlet
valves in their guides. The inlet valves should be a loose
sliding fit in the guides.
During this test, the compressor should be checked for
gasket leakage and noisy operation, as well as unloader
operationandleakage.
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,
andcotterpinsas required and then protecttheendsagainst
damagebywrappingwith masking tapeorfrictiontape. The
open bottom of a vertical engine lubricated compressors
should be protected against the entrance of dirt during
handling or storage, by installing a temporary cover over
the base.
COMPRESSOR TROUBLESHOOTING
IMPORTANT:Thetroubleshootingcontainedinthis section
considers the compressor as an integrated component of
theoverall airbrake charging system and assumesthat an
airdryer is inuse. Thetroubleshooting presentedwill cover
notonlythecompressoritself,butalsootherchargingsystem
devices as they relate to the compressor.
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID
PERSONAL INJURY OR DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all times.
1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
Always wear safety glasses.
2. Stop the engine and remove ignition key when
working under or around the vehicle. When
working in the engine compartment, the engine
should be shut off and the ignition key should be
removed. Where circumstances require that the
enginebeinoperation,EXTREMECAUTIONshould
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. Useonlythepropertoolsandobserve
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™airdryersystemoradryerreservoirmodule,
be sure to drain the purge reservoir.
5. Following the vehicle manufacturer’s
recommendedprocedures,deactivatetheelectrical
systeminamannerthatsafelyremovesallelectrical
power from the vehicle.
FIGURE 16 - UNLOADER MECHANISM
Cylinder Head
Installtheinletvalvespringsinthecylinder head by applying
a turning motion to the spring after it is in the head. The
turning motion should dig the spring wire into the spring
seat in the bottom of the spring bore in the head. Should
thisprocedurefail afterrepeatedattempts, useavery small
quantity of grease to hold them in place, just enough to
keep the springs from failing out. Place the cylinder head
gasket on the cylinder block. Carefully align the cylinder
head assembly on the block and install the cap screws,
tightening them evenly to a torque of 25-30 foot pounds.
Base Plate or Base Adapter
Position the base plate or base adapter gasket on the
crankcase and install the base plate or base adapter as
marked before disassembly. Tighten the six cap screws
securing the cast iron base adapter evenly to a torque of
38-45foot pounds,and 12-16 foot pounds forbase plateor
aluminumcover.
Testing Rebuilt Compressor
In order to properly test a compressor under operating
conditions, a test rack for correct mounting, cooling,
lubricating,and drivingthe compressor is necessary. Such
testsarenotcompulsoryif theunithasbeencarefully rebuilt
by an experienced person. A compressor efficiency or
build-uptest canbe run which is not too difficult.An engine
lubricated compressor must be connected to an oil supply
line of at least 15 P.S.I. pressure during the test and an oil
returnline must beinstalled tokeep the crankcasedrained.
Connectto thecompressor dischargeport, areservoir with
a volume of 1500 cubic inches, including the volume of
connecting line. With the compressor operating at 2100
R.P.M.,the time required toraise the reservoir(s) pressure
from 85 P.S.I. to 100 P.S.I. should not exceed 7 seconds.

12
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
bedesignedspecificallyforsuchapplicationsand
systems.
9. Components with stripped threads or damaged
parts should be replaced rather than repaired. Do
notattemptrepairsrequiringmachiningorwelding
unless specifically stated and approved by the
vehicle and component manufacturer.
10. Prior to returning the vehicle to service, make
certainallcomponentsandsystemsarerestoredto
their proper operating condition.
11. Forvehicles with Antilock TractionControl(ATC),
the ATC function must be disabled (ATC indicator
lampshouldbeON)priortoperforminganyvehicle
maintenance where one or more wheels on a
drive axle are lifted off the ground and moving.
TABULATED DATA
Number of cylinders 2
Bore size 2.625 in.
Stroke 1.50 in.
Piston displacement at 1250 RPM 12 cu. ft.
Piston displacement per revolution 16.5 cu. in.
Maximum recommended RPM
(naturally aspirated) 3000
Minimum coolant flow at maximum RPM 2.5 gal./min.
Horsepower required at 3000 RPM
against 100 PSI head pressure 4.9H.P.
Recommended minimum discharge 5/8 in. OD
line size Copper Tube
Recommended minimum oil return
line size 5/8 in. OD Tubing
Recommended minimum oil supply
line size 1/4 in. OD Tubing
Recommended minimum unloader
line size 1/4 in. OD Tubing
Recommended minimum inlet cavity line
size (when compressor is
connected to engine air cleaner) 5/8 in. ID
minimum
Recommended minimum coolant line
size 1/2 in. OD Tubing
Recommended maximum inlet air
temperature 250°F
Recommended maximum discharge
air temperature 400°F
Minimum pressure required to unload 60 PSI

*This guide is only for vehicles that use desiccant air dryers.
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.
Advanced Troubleshooting Guide
for Air Brake Compressors*
This troubleshooting guide obsoletes and supersedes all previous published
troubleshooting information relative to Bendix air compressors.
Air brake charging system:
Slow build (9.0) . . . . . . . . . . . . . . . . . 21 - 22
Doesn’t build air (10.0) . . . . . . . . . . . . . . . 23
Air dryer:
Doesn’t purge (14.0) . . . . . . . . . . . . . . . . . 24
Safety valve releases air (12.0). . . . . . . . . 24
Compressor:
Constantly cycles (15.0) . . . . . . . . . . . . . . 24
Leaks air (16.0) . . . . . . . . . . . . . . . . . . . . . 25
Safety valve releases air (11.0). . . . . . . . . 23
Noisy (18.0) . . . . . . . . . . . . . . . . . . . . . . . . 25
Reservoir:
Safety valve releases air (13.0). . . . . . . . . 24
INDEX
Air Coolant
Engine
Oil
Compressor leaks coolant (17.0) . . . . . . . . . . 25
Oil consumption (6.0) . . . . . . . . . . . . . . . . . . . 21
Oil Test Card results (1.0) . . . . . . . . . . . . . . . . 16
Oil is present:
On the outside of the compressor (2.0). . . 17
At the air dryer purge/exhaust
or surrounding area (3.0) . . . . . . . . . . . 17
In the supply reservoir (4.0). . . . . . . . 18 - 20
At the valves (5.0) . . . . . . . . . . . . . . . . . . . 20
At air dryer cartridge (7.0) . . . . . . . . . . . . . 21
In the ping tank or compressor
discharge aftercooler (8.0) . . . . . . . . . . 21
Symptom Page Number
(1) Oil Leakage at Head Gasket . . .26
(2) System Leakage . . . . . . . . . . . .26
(3) Compressor Discharge and
Air Dryer Inlet Temperature . . . .26
(4) Governor Malfunction . . . . . . . .27
(5) Governor Control Line . . . . . . . .27
(6) Compressor Unloader . . . . . . . .27
BASIC Test Information . . . . . . 29-31
Test Procedures
Maintenance Schedule and
Usage Guidelines (Table A) . . 15
Symptom Page Number
Maintenance & Usage Guidelines
13

14
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
aircompressor istypically cooledby theengine 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
pressurelevel by monitoring the pressurein theservice
(or“supply”) reservoir. When theair pressurebecomes
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
airpressure dropsto the“cut-in”setting ofthe 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.
Aircompressors are designed to buildair (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 15) 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.
Whenthetemperatureof thecompressedairthatenters
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
dryerandintothe air system. Largerdiameterdischarge
linesand/orlongerdischargelinelengthscanhelpreduce
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 32-34). 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
purgedwhen thegovernor reaches its “cut-out”setting.
Forvehicles with accessoriesthat aresensitive tosmall
amounts of oil, we recommended installation of a
Bendix®PuraGuard®system filter, designedto minimize
the amount of oil present.
Air Dryer
Reservoir Drain
Service Reservoir
(Supply Reservoir)
Compressor
Governor
(Governor plus Synchro valve
for the Bendix®DuraFlo™596™
Compressor)
Discharge
Line Optional “Ping” Tank
Optional Bendix®PuraGuard®
System Filter or PuraGuard®
QC™Oil Coalescing Filter
The Air Brake Charging System supplies the
compressed air for the braking system as well as other
air accessories for the vehicle. The system usually
consists of an air compressor, governor, discharge line,
air dryer, and service reservoir.

15
Compressor with up to 25% duty cycle
Footnotes:
1 With increased air demand the air dryer cartridge needs to be replaced more often.
2 Use the drain valves to slowly drain all reservoirs to zero psi.
3 Allow the oil/water mixture to fully settle before measuring oil quantity.
4 Tocounterabovenormaltemperaturesattheairdryerinlet,(andresultantoil-vaporpassing
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-vaporcondensesandcanberemovedbytheairdryer. Discharge line upgrades are not
coveredunderwarranty. Note:Tohelppreventdischarge line freeze-ups,shorterdischarge
linelengthsorinsulation mayberequiredincoldclimates. (See Bendix BulletinsTCH-08-21
and TCH-08-22, included inAppendix B, for more information.)
5 For certain vehicles/applications, where turbo-charged inlet air is used, a smaller size
compressor may be permissible.
Recom- Recom- Acceptable
Typical Discharge mended mended Reservoir
Compressors Line Air Dryer Reservoir Oil Contents3
No. of Spec'd Cartridge Drain at Regular
Axles Replacement1Schedule2Drain Interval
High Air Use
Low Air Use
e.g. Double/triple trailer, open
highway coach/RV, (most)
pick-up & delivery, yard or
terminal jockey, off-highway,
construction, loggers, concrete
mixer, dump truck, fire truck.
e.g. Line haul single trailer
w/o air suspension, air over
hydraulic brakes.
e.g. Line haul single trailer
with air suspension,
school bus.
e.g. City transit bus, refuse,
bulk unloaders, low boys,
urban region coach, central
tire inflation.
5
or
less
5
or
less
8
or
less
12
or
less
Table A: Maintenance Schedule and Usage Guidelines
Recom-
mended
Every
Month -
Max of
every 90
days
Every
Month
Every 3
Years
Every 2
Years
Every
Year
I.D.
Vehicle Used for:
Column 1 Column 2 Column 3 Column 4 Column 5
Regularly scheduled maintenance is the single most important factor in maintaining the air brake charging system.
Note: Compressor and/or air dryer
upgradesare recommendedin 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.
Length
6 ft.
1/2 in.
9 ft.1/2 in.
12 ft.
1/2 in.
5/8 in. 12 ft.
BASIC test
acceptable
range:
5 oil units
per month.
See
appendix
A.
For oil carry-over
control4 suggested
upgrades:
3/4 in. 15 ft.
For oil carry-over
control4 suggested
upgrades:
5/8 in. 15 ft.
For oil carry-over
control4 suggested
upgrades:
5/8 in. 9 ft.
For oil carry-over
control4 suggested
upgrades:
5/8 in. 12 ft.
Compressor with less than 15% duty
cycle
Compressor with up to 25% duty cycle
Compressor with up to 25% duty cycle
Bendix®BA-921™air compressor
Bendix®Tu-Flo®550 air compressor
Bendix®Tu-Flo®750 air compressor
Bendix®BA-922™, or DuraFlo™596air compressor
BASIC test
acceptable
range:
3 oil units
per month.
See
appendix
A.
For the
BASIC
Test Kit:
Order
Bendix
P/N
5013711

16
ü
Air Brake Charging System Troubleshooting
How to use this guide:
1.0 Oil Test Card
Results Not a valid test. Discontinue using this test.
Do not use this card test to diagnose
compressor "oil passing" issues. They are
subjective and error prone. Use only the
BendixAirSystem InspectionCup(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 29 for a flowchart and expanded
explanation of the checklist used when
conducting the BASIC test.)
Symptom: What it may indicate: What you should do:
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.
Look for:
Normal - Charging system is working within
normal range.
Check - Charging system needs further
investigation.
û
Bendix®
BASIC Test
WARNING! Please READ and follow these instructions to
avoid personal injury or death:
When working on or around a vehicle, the following general
precautions should be observed at all times.
1. Park the vehicle on a level surface, apply the parking
brakes, and always block the wheels. Always wear safety
glasses.
2. Stop the engine and remove ignition key when working
under or around the vehicle. When working in the engine
compartment,theengineshouldbe shut offandtheignition
keyshould be removed. Where circumstancesrequire that
the engine be in operation, EXTREME CAUTION should
be used to prevent personal injury resulting from contact
withmoving,rotating,leaking,heatedorelectricallycharged
components.
3. Donot attempt toinstall,remove,disassembleor assemble
a component until you have read and thoroughly
understand the recommended procedures. Use only the
proper tools and observe all precautions pertaining to use
of those tools.
4. If the work is being performed on the vehicle’s air brake
system, or any auxiliary pressurized air systems, make
certain to drain the air pressure from all reservoirs before
beginning ANY work on the vehicle. If the vehicle is
equipped with an AD-IS™air dryer system or a dryer
reservoir module, be sure to drain the purge reservoir.
5. Following the vehicle manufacturer’s recommended
procedures, deactivate the electrical system in a manner
that safely removes all electrical power from the vehicle.
6. Never exceed manufacturer’s recommended pressures.
7. Never connect or disconnect a hose or line containing
pressure;it maywhip. Never remove a component or plug
unless you are certain all system pressure has been
depleted.
8. Useonly genuine Bendix®replacementparts,components
andkits.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 withAntilock Traction Control (ATC), theATC
function must be disabled (ATC indicator lamp should be
ON) prior to performing any vehicle maintenance where
oneor more wheels on adrive axle are lifted offthe ground
and moving.

Symptom: What it may indicate: What you should do:
17
2.2 Oil leaking
from compressor: (a)Excessive leak at head gasket.
(b)Leak at bottom cover plate.
(c)Leak at internal rear flange gasket.
(d)Leak through crankcase.
(e)(If unable to tell source of leak.)
ðGo to Test 1 on page 26.
ðReseal bottom cover plate using RTV
silicone sealant.
ðReplace compressor.
ðReplace compressor.
ðClean compressor and check periodically.
Air brake charging system functioning
normally.
ðAir dryers remove water and oil from the
air brake charging system.
Check that regular maintenance is being
performed. Return the vehicle to service.
An optional kit (Bendix piece number
5011327 for the Bendix®AD-IS™or AD-IP™
air dryers, or 5003838 for the Bendix®
AD-9™air dryer) is available to redirect the
air dryer exhaust.
3.0 Oil at air dryer
purge/exhaust or
surrounding area
(c)
2.0 Oil on the
Outside of the
Compressor
Find the source and repair. Return the vehicle
to service.
ðRepair or replace as necessary. If the
mounting bolt torques are low, replace the
gasket.
ðReplace the fitting gasket. Inspect inlet
hose and replace as necessary.
ðReplace gasket or fitting as necessary to
ensure good seal.
ðInspect and repair as necessary.
Engine and/or other accessories
leaking onto compressor.
(a)Leak at the front or rear (fuel
pump, etc.) mounting flange.
(b)Leak at air inlet fitting.
(c)Leak at air discharge fitting.
(d)Loose/broken oil line fittings.
2.1 Oil leaking at
compressor / engine
connections:
(a)
ð
ð
Head
gasket
and rear
flange
gasket
locations.
(c)

18
4.0 Oil in Supply or
Service Reservoir
(air dryer installed)
(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.)
(a)If air brake charging system
maintenance has not been
performed.
Thatis, reservoir(s)have not been
drained per the schedule in Table
Aon page15,Column 4 and/or the
air dryer maintenance has not
been performed as in Column 3.
(b)If the vehicle maintenance has
been performed as recom-
mended in Table A on page 15,
someoil in thereservoirs isnormal.
ðDrainall airtanks and check vehicleat next
service interval using the Bendix®BASIC
test. See Table A on page 15, column 3
and4, for recommendedservice schedule.
ðDrain 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 26), 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.
ðIf outside the normal range go to
Symptom 4.0(c).
Also see the Table A on page 15, column
3 for recommended air dryer cartridge
replacement schedule.
Maintenance
(a)
ðGo to Test 2 on page 26.
ðSee Table A, column 1, on page 15 for
recommended compressor sizes.
ðIf 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 costsincurred(e.g.
installing a larger capacity compressor,
etc.) are not covered under original
compressor warranty.
ðIf the compressor is correct for the
vehicle, go to Symptom 4.0 (e).
Duty cycle too high
Symptom: What it may indicate: What you should do:
See Table A, on page 15,
for maintenance
schedule information.
Drain all air tanks (reservoirs)
into the Bendix®BASIC test
cup. (Bendix kit P/N 5013711).
The duty cycle is the ratio of time the compressor spends
building air to total engine running time. Air compressors
are designed to build air (to "run loaded") up to 25% of the
time. Higher duty cycles cause conditions that affect air
brake charging system performance which may require
additional maintenance. Factors that add to the duty cycle
are: air suspension, additional air accessories, use of an
undersized compressor, frequent stops, excessive leakage
from fittings, connections, lines, chambers or valves, etc.
(c)Air brake system leakage.
(d)Compressormay beundersizedfor
the application.

Symptom: What it may indicate: What you should do:
19
(e)Air compressor discharge and/or
airdryer inlettemperature toohigh.
(f) Insufficient coolant flow.
(g)Restricted discharge line.
ðCheck temperature as outlined in Test 3
on page 26. If temperatures are normal
go to 4.0(h).
ðInspectcoolant line. Replace as necessary
(I.D. is 1/2").
ðInspect the coolant lines for kinks and
restrictions and fittings for restrictions.
Replace as necessary.
ðVerify coolant lines go from engine block
tocompressor andback to the water pump.
Repair as necessary.
ðIf discharge line is restricted or more than
1/16" carbon build up is found, replace the
discharge line. See TableA, column 2, on
page 15 for recommended size. Replace
as necessary.
ðThe discharge line must maintain a
constant slope downfrom thecompressor
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
informationonhowtohelppreventdischarge
line freeze-ups, see Bendix Bulletins
TCH-08-21 and TCH-08-22 (Appendix B).
Shorter discharge line lengths or insulation
may be required in cold climates.
Temperature
Other
ðCheck compressor air inlet line for
restrictions, brittleness, soft or sagging
hoseconditions etc. Repair as necessary.
Inlet line size is 3/4 ID. Maximum
restriction requirement for compressors is
25 inches of water.
ðCheck the engine air filter and service if
necessary (if possible, check the air filter
usage indicator).
(h)Restricted air inlet (not enough air
to compressor).
(g)
(h)
4.0 Oil in Supply
or Service
Reservoir*
(air dryer installed)
(continued)
(f)
(e)
(g)
Kinked discharge line shown.
Partly
collapsed
inlet line
shown.
Testing the temperature
at the discharge fitting. Inspecting the coolant hoses.
*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.

Symptom: What it may indicate: What you should do:
20
(i) Poorly filtered inlet air (poor air
quality to compressor).
(j) Governor malfunction or setting.
(k)Compressor malfunction.
4.0 Oil in Supply
or Service
Reservoir*
(air dryer installed)
(continued)
ðCheck for leaking, damaged or defective
compressor air inlet components (e.g.
inductionline, fittings,gaskets,filterbodies,
etc.). Repair inlet components as needed.
Note: Dirt ingestion will damage
compressor and is not covered under
warranty.
ðGo to Test 4 on page 27.
ðIf 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.
Other (cont.)
Inspect the
engine air
cleaner.
** SAE J2024 outlines testsallairbrakesystem pneumatic
componentsneedtobeableto pass,includingminimum
levels of tolerance to contamination.
5.0 Oil present at
valves (e.g. at
exhaust, or seen
during servicing).
Air brake system valves are required
to tolerate a light coating of oil. ðA small amount of oil does not affect SAE
J2024** compliant valves.
ðCheck 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®
BASICtest cup (seealso column 5ofTable
A on page 15). Return the vehicle to
service.
For oil-sensitive systems, see page 14.
Genuine
Bendix
valves are
all SAE
J2024
compliant.
*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.
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.