SD-01-335

Bendix® TU-FLO® 700 Air Compressor

DISCHARGE
CAP NUT DISCHARGE
VALVE UNLOADER
DISCHARGE SPRING MECHANISM
VALVE
DISCHARGE
VALVE SEAT

INLET
VALVE
SPRING
INLET
VALVE
PISTON
RINGS
PISTON

CRANKSHAFT

CONNECTING
EXTERIOR ROD
CRANKCASE BENDIX® TU-FLO® 700 AIR COMPRESSOR
(CROSS SECTION)

DESCRIPTION Two methods are employed for cooling the Tu-Flo® 700
compressor during operation. The cylinder head is
The function of the air compressor is to provide and main- connected to the engine’s cooling system, while the cylinder
tain air under pressure to operate devices in the air brake has external fins for efficient air cooling.
and/or auxiliary air systems
All Tu-Flo® 700 compressors utilize the engine’s pressurized
The Tu-Flo® 700 compressor is a two cylinder, single stage, oil system to lubricate the internal moving parts. A nameplate
reciprocating compressor with a rated displacement of 15.5 is attached to the crankcase to identify the compressor.
cubic feet of air per minute at 1250 R.P.M. The Tu-Flo® 700 The nameplate displays a Bendix piece number or in some
compressor is constructed from three major assemblies, cases an engine or vehicle manufacturer’s piece number,
the head, the cylinder block and the crankcase. along with a serial number.
The head houses the discharge valving and is installed on
the upper portion of the cylinder block. The cylinder block
TU-FLO 700
contains the cylinder bores and inlet valves and is mounted
BW
to the crankcase. The crankcase houses the crankshaft NO.
and main bearings.
SER
NO.
Various mounting and drive configurations, required by the MANUFACTURED BY

numerous vehicle engine designs, are available. Two BENDIX

governor mounting pads are located on either side of the

cylinder block to provide convenient governor mounting. COMPRESSOR NAMEPLATE

1
 MACK
"FOXHEAD"
CUMMINS

VARIOUS COMPRESSOR MOUNTINGS

DETROIT
DIESEL
MACK

OPERATION reservoir into the cavity beneath the unloader pistons. This
lifts the unloader pistons and plungers. The plungers move
The compressor is driven by the vehicle engine and is up and hold the inlet valves off their seats (see Figure 4).
operating continuously while the engine is running. Actual
compression of air is controlled by the compressor unloading With the inlet valves held off their seats by the unloader
mechanism and the governor. The governor is generally pistons and plungers, air is pumped back and forth between
mounted on the compressor and maintains the brake system the two cylinders. When air is used from the reservoir and
air pressure to a preset maximum and minimum pressure the pressure drops to the cut-in setting of the governor, the
level. governor closes and exhausts the air from beneath the
unloader pistons. The unloader saddle spring forces the
INTAKE AND COMPRESSION OF AIR (LOADED) saddle, pistons and plungers down and the inlet valves return
to their seats. Compression is then resumed.
During the down stroke of the piston, a slight vacuum is
created between the ton of the piston and the head, causing
COMPRESSOR & THE AIR BRAKE SYSTEM
the flat circular inlet valve to move up and off its seat. (Note
the flat square discharge valve remains on its seat.) GENERAL
Atmospheric air is drawn through the air strainer by the open
The compressor is part of the total air brake system, more
inlet valve and into the cylinder (see Fig. 2). As the piston
specifically, the charging portion of the air brake system. As
begins its upward stroke, the air that was drawn into the
a component in the overall system its condition, duty cycle,
cylinder on the down stroke is being compressed. Air
proper installation and operation will directly affect other
pressure on top of the inlet valve plus the force of its spring,
components in the system.
returns the inlet valve to its seat. The piston continues the
upward stroke and compressed air then flows by the open Powered by the vehicle engine, the air compressor builds
discharge valve, into the discharge line and on to the the air pressure for the air brake system. The air compressor
reservoirs (see Fig. 3). As the piston reaches the top of its is typically cooled by the engine coolant system, lubricated
stroke and starts down, the discharge valve spring and air by the engine oil supply and has its inlet connected to the
pressure in the discharge line returns the discharge valve to engine induction system.
its seat. This prevents the compressed air in the discharge
As the atmospheric air is compressed, all the water vapor
line from returning to the cylinder bore as the intake and
originally in the air is carried along into the air system, as
compression cycle is repeated.
well as a small amount of the lubricating oil as vapor. If an
NON-COMPRESSION OF AIR (UNLOADED) air dryer is not used to remove these contaminants prior to
entering the air system, the majority, but not all, will condense
When air pressure in the reservoir reaches the cut-out setting in the reservoirs. The quantity of contaminants that reach
of the governor, the governor allows air to pass from the the air system depends on several factors including
2
 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
Discharge Optional “Ping” Tank of an air compressor, governor, discharge line, air dryer,
Line Air Dryer and service reservoir.

Optional Bendix® PuraGuard® QC™

Oil Coalescing Filter

Compressor
Governor
(Governor plus Synchro valve Service Reservoir
for the Bendix® DuraFlo™ 596 (Supply Reservoir)
Compressor)
Reservoir Drain

FIGURE 1A - SYSTEM DRAWING

installation, maintenance and contaminant handling devices The discharge line must maintain a constant slope down
in the system. These contaminants must either be eliminated from the compressor to the air dryer inlet fitting or reservoir
prior to entering the air system or after they enter. to avoid low points where ice may form and block the flow. If,
instead, ice blockages occur at the air dryer or reservoir
DUTY CYCLE
inlet, insulation may be added here, or if the inlet fitting is a
The duty cycle is the ratio of time the compressor spends typical 90 degree fitting, it may be changed to a straight or
building air to the total engine running time. Air compressors 45 degree fitting. Shorter discharge line lengths or insulation
are designed to build air (run "loaded") up to 25% of the may be required in cold climates.
time. Higher duty cycles cause conditions that affect air
While not all compressors and charging systems are
brake charging system performance which may require
equipped with a discharge line safety valve this component
additional maintenance. Factors that add to the duty cycle
is recommended. The discharge line safety valve is installed
are: air suspension, additional air accessories, use of an
in the cylinder head (Tu-Flo® 550/750) or close to the
undersized compressor, frequent stops, excessive leakage
compressor discharge port and protects against over
from fittings, connections, lines, chambers or valves, etc.
pressurizing the compressor in the event of a discharge line
Refer to Table A in the Troubleshooting section for a guide to
freezeup.
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 HOLE
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 THREAD
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
FIGURE 1B - DISCHARGE LINE SAFETY VALVE
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.

3
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
TO RESERVOIR
of the compressed air is above the normal range, oil as oil- DISCHARGE INLET VALVE
vapor is able to pass through the air dryer and into the air VALVE
UNLOADER
system. Larger diameter discharge lines and/or longer PLUNGER
discharge line lengths can help reduce the temperature.
PISTON INTAKE
The air dryer contains a filter that collects oil droplets, and a STRAINER
desiccant bed that removes almost all of the remaining water
vapor. The compressed air is then passed to the air brake TO GOVERNOR
service (supply) reservoir. The oil droplets and the water
collected are automatically purged when the governor STROKE
reaches its "cut-out" setting.

For vehicles with accessories that are sensitive to small FIGURE 2 - INTAKE
amounts of oil, we recommend installation of a Bendix®
PuraGuard® QC™ oil coalescing filter, designed to minimize
the amount of oil present.

LUBRICATION
Since all Tu-Flo® 700 compressors are connected to the TO RESERVOIR
DISCHARGE
engine’s pressurized oil system, a continuous flow of oil is VALVE INLET VALVE
provided to the compressor, which is eventually returned to UNLOADER
PLUNGER
the engine. Oil is fed into the compressor in various ways,
for example: through the rear end cover, the drive end of the PISTON INTAKE
crankshaft or through the front flange adapter. An oil passage STRAINER
in the crankshaft conducts pressurized oil to the precision
sleeve main bearings and to the connecting rod bearings.
Splash lubrication of the cylinder bores, connecting rod wrist TO GOVERNOR
STROKE
pin bushings, and the ball type main bearings, on some
models, is obtained as oil is forced out around the crankshaft
journals by engine oil pressure.

Check the exterior of the compressor for the presence of oil FIGURE 3 - COMPRESSION
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 TO RESERVOIR
majority of oil prior to entrance into the air brake system. DISCHARGE
VALVE INLET VALVE
For particularly oil sensitive systems the Bendix® PuraGuard® UNLOADER
QC™ oil coalescing filter can be used in conjunction with a PLUNGER
PISTON
Bendix air dryer.
INTAKE
If compressor oil passing is suspected, refer to the STRAINER
TROUBLESHOOTING section and TABLE A for the
symptoms and corrective action to be taken. In addition, TO GOVERNOR
Bendix has developed the "Bendix Air System Inspection
STROKE
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. FIGURE 4 - UNLOADING

4
COOLING DRY ELEMENT—PLEATED PAPER AIR
STRAINER
Air flowing through the engine compartment from the action
of the engine’s fan and the movement of the vehicle assists Every 20,000 miles or 800 operating hours:
in cooling the crankcase. Coolant flowing from the engine’s Remove the spring clips from either side of mounting baffle
cooling system through connecting lines enters the and remove the cover. Replace the pleated paper filter and
compressor and flows through the internal passages in the remount the cleaned cover making sure the filter is in
cylinder block and head and back to the engine. Proper position. Be sure to replace the air strainer gasket if the
cooling is important in maintaining discharge air temperatures entire air strainer is removed from the compressor intake.
below the 400°F recommended maximum. (Note: Some compressors are fitted with compressor intake
adapters which allow the compressor intake to be connected
PREVENTIVE MAINTENANCE
to the engine air cleaner.) In this case, the compressor
Regularly scheduled maintenance is the single most receives a supply of clean air from the engine air cleaner.
important factor in maintaining the air brake charging system. When the engine air filter is changed, the compressor intake
Refer to Table A in the Troubleshooting section for a guide to adapter should be checked. If it is loose, remove the intake
various considerations that must be given to the maintenance adapter, clean the strainer plate, if applicable, and replace
of the compressor and other related charging system the intake adapter gasket, and reinstall the adapter securely.
components. Check line connections both at the compressor intake
adapter and at the engine air cleaner. Inspect the connecting
Important Note: Review the warranty policy before
line for ruptures and replace it if necessary.
performing any intrusive maintenance procedures. An
extended warranty may be voided if intrusive maintenance
is performed during this period.

Every month, 300 operating hours or after each 10,000 miles,

depending on the operating conditions, experience and the
type of strainer used, service the air 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
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
FIGURE 6 - PAPER AIR STRAINER DRY ELEMENT-
entire air strainer is removed from the compressor intake. PLEATED

FIGURE 7 - COMPRESSOR INTAKE ADAPTER

FIGURE 5 - POLYURETHANE SPONGE STRAINER

5
Every 6 months, 1800 operating hours or after each 85-100 P.S.I. in 25 seconds or less. This test is performed
50,000 miles: with the engine operating at maximum governed speed. The
vehicle manufacturer must certify this performance on new
Remove the discharge head fittings and inspect the
vehicles with appropriate allowances for air systems with
compressor discharge port and discharge line for excessive
greater than the minimum required reservoir volume.
carbon deposits. If excessive buildup is noted in either, the
discharge line must be cleaned or replaced and the
AIR LEAKAGE TESTS
compressor checked more thoroughly, paying special
attention to the air induction system, oil supply and return Leakage past the discharge valves can be detected by
system, and proper cooling. If necessary, repair or replace removing the discharge line, applying shop air back through
the compressor. Check for proper belt and pulley alignment the discharge port and listening for escaping air. Also, the
and belt tension. Adjust if necessary, paying special attention discharge valves and the unloader pistons can be checked
not to over tighten the belt tension. Check for noisy for leakage by building up the air system until the governor
compressor operation, which could indicate a worn drive cuts out, then stopping the engine. With the engine stopped,
gear coupling or a loose pulley. Adjust and/or replace as listen for escaping air at the compressor intake. To pinpoint
necessary. Check all compressor mounting bolts and leakage if noted, apply a small quantity of oil around the
retighten evenly if necessary. Check for leakage and proper unloader pistons. If there is no noticeable leakage at the
unloader mechanism operation. Replace if defective in any unloader pistons, the discharge valves may be leaking. If
way. the compressor does not function as described above, or
leakage is excessive, it is recommended that it be returned
Every 24 months, 7200 operating hours or after each to the nearest authorized Bendix Distributor for a factory
200,000 miles: remanufactured compressor. If this is not possible, the
Perform a thorough inspection as indicated below and compressor can be repaired using genuine Bendix
depending upon the results of this inspection or experience, replacement parts, in which case, the following information
disassemble the compressor, clean and inspect all parts should prove helpful.
thoroughly, repair or replace all worn or damaged parts using
only genuine Bendix replacements or replace the REMOVING AND DISASSEMBLY
compressor with a genuine Bendix remanufactured unit.
REMOVING
Important: Should it be necessary to drain the engine cooling
system to prevent damage from freezing, the cylinder head These instructions are general and are intended to be a
of the compressor must also be drained. guide, in some cases additional preparations and precautions
are necessary. Chock the wheels of the vehicle and drain
GENERAL SERVICE CHECKS the air pressure from all the reservoirs in the system. Drain
the engine cooling system and the cylinder head of the
INSPECTION compressor. Disconnect all air, water and oil lines leading
to and from the compressor. Remove the drive gear(s) or
It is of the utmost importance that the compressor receives
pulley from the compressor crankshaft using a gear puller.
a clean supply of air. The air strainer must be properly
Inspect the pulley or gear and associated parts for visible
installed and kept clean. If the compressor intake is connected
wear or damage. Since these parts are precision fitted, they
to the engine air cleaner, supercharger, etc., these
must be replaced if they are worn or damaged.
connections must be properly installed and maintained.
Check the compressor mountings to be sure they are secure.
DISASSEMBLY
Check the drive for proper alignment, belt tension, etc.

Inspect the oil supply and return lines. Be sure these lines GENERAL
are properly installed and that the compressor is getting the Remove road dirt and grease from the exterior of the
proper supply of oil, and just as important, that the oil is compressor with a cleaning solvent. Before the compressor
returning to the engine. Check the coolant lines to and from is disassembled, the following items should be marked to
the compressor and see that the cooling fins on the show their relationship when the compressor is assembled.
crankcase are not clogged with dirt, grease, etc. Check the Mark both the front and rear end cover in relation to the
unloader mechanism for proper and prompt operation. crankcase. Mark the drive end of the crankshaft in relation
to the front end cover and the crankcase. Mark the cylinder
OPERATING TESTS head in relation to the block and the block in relation to the
Vehicles manufactured after the effective date of FMVSS crankcase. Mark the base plate or base adapter in relation
121, with the minimum required reservoir volume, must have to the crankcase.
a compressor capable of raising air system pressure from
6
A convenient method to indicate the above relationship is to Discard the inlet valves (3) and springs (2), the discharge
use a metal scribe to mark the parts with numbers or lines. valves (7), springs (8) and the discharge valve seats (6) if
Do not use a marking method that can be wiped off or defective.
obliterated during rebuilding, such as chalk. Remove all
compressor attachments such as governors, air strainers CRANKCASE BASE PLATE OR ADAPTER
or inlet fittings, discharge fittings and pipe plugs. Remove the cap screws securing the base plate or base
adapter. Tap with soft mallet to break the gasket seal (11).
CYLINDER HEAD Scrape off any gasket material from crankcase and plate or
Remove the six cylinder head cap screws (1) and tap the adapter.
head with a soft mallet to break the gasket seal. Remove
the inlet valve springs (2) and spring inserts (35) from the CONNECTING ROD ASSEMBLIES
head and inlet valves (3) from their guides in the block. (Note: Before removing the connecting rods, mark each
Remove inlet valve guides (4) from around the inlet valve connecting rod and its cap. Each connecting rod is matched
seats (34) on the block taking care not to damage seats. to its own cap for proper bearing fit, and these parts must
Scrape off any gasket material (5) from the cylinder head not be interchanged.) Remove the connecting rod bolts (13)
and block. Unscrew the discharge valve seats (6) from the and bearing caps (14). Push the piston (15) with the
head and remove the discharge valves (7) and springs (8). connecting rods (16) attached out the top of the cylinders of
Inspect the discharge valve seats (2) for nicks, cracks, and the cylinder block. Replace the bearing caps (14) on their
excessive wear and replace if necessary. The discharge valve respective connecting rods. Remove the piston rings from
cap/nut stops (9) should be inspected for wear and replaced the pistons. If the pistons are to be removed from the
if excessive peening has occurred. To determine if excessive connecting rods, remove the teflon plugs (36) and press the
peening has occurred, measure the discharge valve travel. wrist pins (37) from the pistons and connecting rods.
Discharge valve travel must not exceed .046 inches. If
discharge valve travel is excessive, replace the cap nut/stop
assembly, discharge valve and spring.

9
1
CYLINDER HEAD

8
34
7 35
6 5
18
20 2
19 3
18 4
19
15 10
20 36 36
37 34
CYLINDER BLOCK 35
33
23 37
28
21 12 REAR COVER
16

17
24 26 30
FLANGE 27 22 29
ADAPTER 31
32

REAR COVER
CRANKSHAFT GASKET
14 11
26
13 CRANKCASE
25

FIGURE 8 - TU-FLO® 700 AIR COMPRESSOR (THRU DRIVE) EXPLODED VIEW

7
If the pistons are removed from the rod, inspect the bronze CYLINDER BLOCK
wrist pin bushing. Press out and replace the bushing if it is
Clean the carbon and dirt from the inlet and unloader
excessively worn. (See inspection of parts) Discard the piston
passages. Use shop air pressure to blow the carbon and
rings (18-20) and the connecting rod journal bearings (17).
dirt deposits from the unloader passages.
Discard the wrist pin bushings (21) if they were removed.
OIL PASSAGES
CYLINDER BLOCK
Thoroughly clean all oil passages through the crankshaft,
If the compressor is fitted with an air strainer, inlet elbow or
crankcase, end covers, and base plate or base adapter.
governor remove the same.
Inspect the passages with a wire to be sure. Blow the
Remove cap screws (23) securing cylinder block to the loosened foreign matter out with air pressure.
crankcase; separate the crankcase and cylinder block and
scrape off any gasket material. INSPECTION OF PARTS
Remove the unloader spring (34), spring saddle (35), and CYLINDER HEAD BODY
spring seat (36) from the inlet cavity of the crankcase, using
long nose pliers. With the use of shop air blow the unloader Inspect the cylinder head for cracks or damage. Apply shop
air pressure to one of the coolant ports with all others
plungers (37) and guides (33) out of the cylinder block.
plugged, and check for leakage by applying a soap solution
The inlet valve seats can be removed if worn or damaged to the exterior of the body. If leakage is detected, replace
and are being replaced. Unloader bore bushings should be the head.
inspected but not removed unless they are damaged. If
bushings are to be replaced, they can be removed by running END COVERS
a 1/8" pipe threaded rod and pulling the bushing straight up
Check for cracks and external damage. If the crankshaft
and out. Do not use "easy out" for removing the bushings. main bearings are installed in the end cover, check for
excessive wear and flat spots and replace them if necessary.
CRANKCASE
If the compressor has an oil seal in the end cover, it should
Remove the key (22) or keys from the crankshaft and any be removed by pressing it out of the end cover.
burrs on the crankshaft where the key or keys were removed.
CRANKCASE
(Note: Through drive compressors may have a crankshaft
key at both ends.) Remove the four cap screws (23) securing Check all crankcase surfaces for cracks and damage. On
front or drive-end end cover or flange adapter. Remove the compressors where ball bearing main bearings are used the
end cover, taking care not to damage the crankshaft oil seal difference between the O.D. of the outer race and the I.D. Of
(27) or front main bearing (26), if any. Remove the o-ring (24) the crankcase hole should be .0000 in. to .0015 in. loose.
from around the front end cover. Remove the four cap screws This is to maintain the correct press fit. The crankcase must
(30) securing the rear end cover and remove the rear end be replaced if the fit is too loose.
cover taking care not to damage the rear main bearing (29),
On compressors fitted with precision, sleeve main bearings,
if any. Remove the o-ring (31) from around the end cover. If the difference between the O.D. of the crankshaft journal
the compressor has ball type main bearings, press the
and the main bearing I.D. must not exceed .0065 in. If the
crankshaft and ball bearings from the crankcase, then press
clearance is greater than .0065 in., the end cover or main
the ball bearings from the crankshaft. bearing must be replaced.

CLEANING OF PARTS CYLINDER BLOCK

GENERAL Check the unloader bore bushings to be sure they are not
worn, rusted, or damaged. If these bushings are to be
All parts should be cleaned in a good commercial grade
replaced, they can be removed by running a 1/8 in. pipe
solvent and dried prior to inspection.
thread tap into the bushing, and inserting a 1/8 in. pipe
threaded rod and pulling the bushing straight up and out. Do
CYLINDER HEAD
not use an easy-out for removing these bushings. If the inlet
Remove all the carbon deposits from the discharge cavities valve seats are worn or damaged, so they cannot be
and all the rust and scale from the cooling cavities of the reclaimed by facing, they should be replaced. Cylinder bores
cylinder head body. Scrape all the foreign matter from the should be checked with inside micrometers or calipers (see
body surfaces and use shop air pressure to blow the dirt Figure 9). Cylinder bores which are scored or out of round
particles from all the cavities. by more than .001 in. or tapered more than .002 in. should

8
be rebored or honed oversize. Oversized pistons and piston
rings are available in .010 in., .020 in. and .030 in. oversizes.
Cylinder bores must be smooth, straight, and round.
Clearance between the cast iron pistons and cylinder bores
PISTON
should be between .002 in. minimum and .004 in. maximum. RINGS .002
.004

OIL RING STANDARD

PISTON
RING

.000
.006
EXPANDER
RING
PISTON OIL RING
RING

OIL RING .002"

END GAP .010"

FIGURE 9 - MEASURING CYLINDER BORES FIGURE 10 - CORRECT GROOVE CLEARANCE

PISTONS
CRANKSHAFT
Check the pistons for scores, cracks, or enlarged ring
grooves; replace the pistons if any of these conditions are Check the crankshaft threads, keyways, tapered ends and
found. Measure each piston with a micrometer in relation to all machined and ground surfaces for wear, scores, or
the cylinder bore diameter to be sure the diametral clearance damage. Standard crankshaft journals are 1.1250 in.- 1.1242
is between .002 in. minimum and .004 in. maximum. in. in diameter. If the crankshaft journals are excessively
scored or worn or out of round and cannot be reground, the
Check the fit of the wrist pins to the pistons and connecting crankshaft must be replaced. Connecting rod bearing inserts
rod bushings. The wrist pin should be a light press fit in the are available in .010 in., .020 in. and .030 in. undersizes for
piston. If the wrist pin is a loose fit, the piston and pin compressors with reground crankshafts. Main bearing
assembly should be replaced. Check the fit of the wrist pin journals must be maintained so the ball bearings are a snug
in the connecting rod bushing by rocking the piston. This fit or so that no more than .0065 in. clearance exists between
clearance should not exceed .0007 in. Replace the wrist pin the precision sleeve main bearing and the main bearing
bushings if excessive clearance is found. Wrist pin bushings journals on the crankshaft. In crankshafts fitted with oil seal
should be reamed to between .5314 in. and .5317 in. after rings, the oil seal ring groove or grooves must not be worn.
being pressed into the connecting rods. The ring groove walls must have a good finish and they must
be square. Check to be sure the oil passages are open
Check the fit of the piston rings in the piston ring grooves.
through the crankshaft.
Check the ring gap with the rings installed in the cylinder
bores. Refer to Figure 10 for correct gap and groove
CONNECTING ROD BEARINGS
clearances.
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 each other.
Clearance between the connecting journal and the
connecting rod bearing must not be less than .0003 in. or
more than .0021 in. after rebuilding.

9
REPAIRS ASSEMBLY
General Note: All torques specified in this manual are
DISCHARGE VALVES, VALVE STOPS AND
assembly torques and can be expected to fall off after
SEATS assembly is accomplished. Do not retorque after initial
If the discharge valve seats merely show signs of slight wear, assembly torques fall.
they can be dressed by using a lapping stone, grinding
To convert inch pounds of torque to foot pounds of torque,
compound and grinding tool. Install the new discharge valve
divide inch pounds by 12.
springs and valves. Screw in the discharge valve seats.
Discharge valve travel should be between .030 in. to .046 in. inch pounds ÷ 12 = foot pounds
To test for leakage by the discharge valves, apply 100 pounds To convert foot pounds of torque to inch pounds of torque,
of air pressure through the cylinder head discharge port and multiply foot pounds by 12.
apply a soap solution to the discharge valves and seats. A
slight leakage in the form of soap bubbles is permissible. If foot pounds x 12 = inch pounds
excessive leakage is found, leave the air pressure applied
and with the use of a fiber or hardwood dowel and a hammer,
INSTALLING THE CRANKSHAFT
tap the discharge valves off their seats several times. This Press new sleeve bearings in the end cover and crankcase.
will help the valves to seat and should reduce the leakage. Ensure that the slot in the bearings line up with the oil
With the air pressure still applied at the discharge port of passages in the end cover or crankcase. If you have a model
the cylinder head, check for leakage around the discharge with no oil passage present in the crankcase, press the
valve cap nut on the top of the cylinder head casting. No sleeve bearing into the crankcase with the slot located 90
leakage is permitted. degrees from vertical.

INLET VALVES AND SEATS Install the front thrust washer with the tang inserted in the
slot toward the flange. Insert the crankshaft and the rear
Inlet valves and springs should be replaced, if the inlet valve thrust washer with the tang toward the rear of the compressor.
seats show signs of slight nicks or scratches. They can be
redressed with a fine piece of emery cloth or by lapping with Place the oil seal ring on the boss of the rear end cover and
a lapping stone, grinding compound and grinding tool. If the install the end cover making sure not to pinch the seal ring.
seats are damaged to the extent that they cannot be Ensure the tang of the thrust washer is inserted in the slot
reclaimed, they must be replaced. The dimension from the of the end cover. Fasten the end cover to the crankcase with
top of the cylinder block to the inlet valve seat should not the four cover cap screws. Torque the cap screws to 175-
exceed .113 in. nor be less than .101 in. 225 inch pounds in a cross pattern. 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
2 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
3
to 15-18 foot pounds. For through drive compressors with a
cast iron end cover, torque the four 7/16 in. cap screws to
4
25-30 foot pounds.

10 PISTONS AND CONNECTING RODS

8 7 If new wrist pin bushings are to be used, they should be
6 pressed into the connecting rods so that the oil hole in the
bushing lines up with the one in the rod. The new bushings
DISCHARGE VALVE, should then be reamed or honed to provide between .0001
VALVE STOP INLET VALVE
in. (.00254 mm) and .0006 in. (.01524 mm) clearance on
AND SEAT AND SEAT
the wrist pin. Position the connecting rod in the piston and
press in the wrist pin.
FIGURE 11 FIGURE 12
Pistons installed in compressors manufactured prior to
November, 1976, will have the wrist pin secured in the piston
by a lock wire extending through matching holes in wrist pin
and piston boss, anchored in a hole in the side wall of the
piston. If the original pistons are used the wrist pin must be
pressed in so the hole in the wrist pin aligns with that of the
10
piston and secure same by inserting the new lockwire CYLINDER HEAD
through the hole in piston and wrist pin and lock the wire by
Install the inlet valve springs in the cylinder head by applying
snapping the short 90 section into the lockwire hole in the
a turning motion to the spring after it is in the head. The
bottom of the piston.
turning motion should dig the spring wire into the spring
Compressors built after November, 1976, will have the wrist seat in the bottom of the spring bore in the head. Should
pin secured by Teflon buttons in either end of the wrist pin, this procedure fail after repeated attempts, use a very small
allowing the wrist pin to float. The Teflon buttons pc. no. quantity of grease to hold them in place, just enough to
292392 may be used with either new or old wrist pins. The keep the springs from falling out. Place the cylinder head
later design pistons have two rings above the wrist pin and gasket on the cylinder block. Carefully align the cylinder
one below. Install the piston rings in the correct location head assembly on the block and install the cap screws,
with the ring pipmarks up. Stagger the position of the ring tightening them evenly to a torque of 15-19 foot pounds.
gaps. Prelubricate the piston, piston rings, wrist pins and
connecting rod. BASE PLATE OR BASE ADAPTER
Position the base plate or base adapter gasket on the
CYLINDER BLOCK crankcase and install the base plate or base adapter as
Align gasket (12), crankcase and cylinder block and secure marked before disassembly. Tighten the six cap screws
with cap screws (23). Torque to 15-19 foot pounds. securing the cast iron base adapter evenly to a torque of 38-
45 foot pounds, and 12-16 foot pounds for base plate or
UNLOADER aluminum cover.
A new unloader kit should used when rebuilding. (Figure
TESTING REBUILT COMPRESSOR
13). (Piece Number 279615). The unloader pistons in the kit
are prelubricated with a special lubricant piece number In order to properly test a compressor under operating
239379 and need no additional lubrication. Install the unloader conditions, a test rack for correct mounting, cooling,
pistons (28) in their bores being careful not to cut the lubricating, and driving the compressor is necessary. Such
o-rings. Position the unloader plungers (37) in their guides tests are not compulsory if the unit has been carefully rebuilt
(38) and slip them in and over the tops of the pistons. Install by an experienced person. A compressor efficiency or build-
the unloader spring seat (36) in the cylinder block inlet cavity; up test can be run which is not too difficult. An engine
a small hole is drilled in the cylinder block for this purpose. lubricated compressor must be connected to an oil supply
Position the saddle (35) between the unloader piston guides line of at least 15 P.S.I. pressure during the test and an oil
(38), so its forks are centered on the guides. Install the return line must be installed to keep the crankcase drained.
unloader spring (34), making sure it seats over the spring
Connect to the compressor discharge port, a reservoir with
seats both in the block and on the saddle. Position and
a volume of 1500 cubic inches, including the volume of
install the inlet valve guides (38), then drop the inlet valves in
connecting line. With the compressor operating at 2100
their guides. The inlet valves should be a loose sliding fit in
R.P.M., the time required to raise the reservoir(s) pressure
the guides.
from 85 P.S.I. to 100 P.S.I. should not exceed 7 seconds.
During this test, the compressor should be checked for
gasket leakage and noisy operation, as well as unloader
operation and leakage.
36
38 INSPECTION OF REBUILT UNIT
Check to be sure that covers, plugs, or masking tape are
34
37 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 tape or friction tape. 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
28 base.

35

FIGURE 13 - UNLOADER MECHANISM

11
COMPRESSOR TROUBLESHOOTING 8. Use only genuine Bendix® replacement parts,
components and kits. Replacement hardware,
IMPORTANT: The troubleshooting contained in this section tubing, hose, fittings, etc. must be of equivalent
considers the compressor as an integrated component of size, type and strength as original equipment and
the overall air brake charging system and assumes that an be designed specifically for such applications and
air dryer is in use. The troubleshooting presented will cover systems.
not only the compressor itself, but also other charging system 9. Components with stripped threads or damaged
devices as they relate to the compressor. 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.
WARNING! PLEASE READ AND FOLLOW
10. Prior to returning the vehicle to service, make
THESE INSTRUCTIONS TO AVOID certain all components and systems are restored to
PERSONAL INJURY OR DEATH: their proper operating condition.
When working on or around a vehicle, the following 11. For vehicles with Antilock Traction Control (ATC),
general precautions should be observed at all times. the ATC function must be disabled (ATC indicator
lamp should be ON) prior to performing any vehicle
1. Park the vehicle on a level surface, apply the
maintenance where one or more wheels on a
parking brakes, and always block the wheels.
drive axle are lifted off the ground and moving.
Always wear safety glasses.
2. Stop the engine and remove ignition key when TABULATED DATA
working under or around the vehicle. When
working in the engine compartment, the engine Number of cylinders ............................ 2
should be shut off and the ignition key should be Bore size ............................................ 2.75 in.
removed. Where circumstances require that the Stroke ................................................. 1.81 in.
engine be in operation, EXTREME CAUTION should Piston displacement at 1250 RPM ...... 15.5 cu. ft.
be used to prevent personal injury resulting from Maximum recommended RPM
contact with moving, rotating, leaking, heated or (naturally aspirated) ............................. 3000
electrically charged components. Minimum coolant flow at maximum
3. Do not attempt to install, remove, disassemble or RPM ................................................... 2.5 gal./min.
assemble a component until you have read and Recommended minimum
thoroughly understand the recommended discharge line size .............................. 5/8 in. OD
procedures. Use only the proper tools and observe
Copper Tube
all precautions pertaining to use of those tools.
Recommended minimum oil
4. If the work is being performed on the vehicle’s air
return line size .................................... 5/8 in. OD Tubing
brake system, or any auxiliary pressurized air
Recommended minimum oil
systems, make certain to drain the air pressure
from all reservoirs before beginning ANY work on supply line size ................................... 1/4 in. OD Tubing
the vehicle. If the vehicle is equipped with an Recommended minimum unloader
AD-IS™ air dryer system or a dryer reservoir module, line size .............................................. 1/4 in. OD Tubing
be sure to drain the purge reservoir. Recommended minimum coolant
5. Following the vehicle manufacturer’s line size .............................................. 1/2 in. OD Tubing
recommended procedures, deactivate the electrical Recommended maximum inlet
system in a manner that safely removes all electrical air temperature .................................... 250°F
power from the vehicle. Recommended maximum
6. Never exceed manufacturer’s recommended discharge air temperature .................... 400°F
pressures. Minimum pressure required
7. Never connect or disconnect a hose or line
to unload ............................................. 60 PSI
containing pressure; it may whip. Never remove a
component or plug unless you are certain all
system pressure has been depleted.

12
 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 Symptom Page Number

Air Coolant
Air brake charging system: Compressor leaks coolant (17.0) . . . . . . . . . . 25
Slow build (9.0) . . . . . . . . . . . . . . . . . 21 - 22
Engine
Doesn’t build air (10.0) . . . . . . . . . . . . . . . 23
Air dryer: Oil consumption (6.0) . . . . . . . . . . . . . . . . . . . 21
Doesn’t purge (14.0) . . . . . . . . . . . . . . . . . 24
Oil
Safety valve releases air (12.0) . . . . . . . . . 24
Compressor: Oil Test Card results (1.0) . . . . . . . . . . . . . . . . 16
Constantly cycles (15.0) . . . . . . . . . . . . . . 24 Oil is present:
Leaks air (16.0) . . . . . . . . . . . . . . . . . . . . . 25 On the outside of the compressor (2.0) . . . 17
Safety valve releases air (11.0) . . . . . . . . . 23 At the air dryer purge/exhaust
Noisy (18.0) . . . . . . . . . . . . . . . . . . . . . . . . 25 or surrounding area (3.0) . . . . . . . . . . . 17
Reservoir: In the supply reservoir (4.0) . . . . . . . . 18 - 20
Safety valve releases air (13.0) . . . . . . . . . 24 At the valves (5.0) . . . . . . . . . . . . . . . . . . . 20
At air dryer cartridge (7.0) . . . . . . . . . . . . . 21
In the ping tank or compressor
discharge aftercooler (8.0) . . . . . . . . . . 21

Test Procedures Maintenance & Usage Guidelines

(1) Oil Leakage at Head Gasket . . . 26 Maintenance Schedule and

(2) System Leakage . . . . . . . . . . . . 26 Usage Guidelines (Table A) . . 15

(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 . . . . . . 28-30

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

13
 Introduction to the Air Brake Charging System
Powered by the vehicle engine, the air compressor air dryer. The typical size of a vehicle's discharge line,
builds the air pressure for the air brake system. The (see column 2 of Table A on page 15) assumes a
air compressor is typically cooled by the engine coolant compressor with a normal (less than 25%) duty cycle,
system and lubricated by the engine oil supply. operating in a temperate climate. See Bendix and/or
The compressor's unloader mechanism and governor other air dryer manufacturer guidelines as needed.
(along with a synchro valve for the Bendix® DuraFlo™ When the temperature of the compressed air that enters
596 air compressor) control the brake system air the air dryer is within the normal range, the air dryer can
pressure between a preset maximum and minimum remove most of the charging system oil. If the
pressure level by monitoring the pressure in the service temperature of the compressed air is above the normal
(or “supply”) reservoir. When the air pressure becomes range, oil as oil-vapor is able to pass through the air
greater than that of the preset “cut-out”, the governor dryer and into the air system. Larger diameter discharge
controls the unloader mechanism of the compressor lines and/or longer discharge line lengths can help reduce
to stop the compressor from building air and also the temperature.
causes the air dryer to purge. As the service reservoir The discharge line must maintain a constant slope
air pressure drops to the “cut-in” setting of the governor, down from the compressor to the air dryer inlet fitting
the governor returns the compressor back to building to avoid low points where ice may form and block the
air and the air dryer to air drying mode. flow. If, instead, ice blockages occur at the air dryer
As the atmospheric air is compressed, all the water inlet, insulation may be added here, or if the inlet fitting
vapor originally in the air is carried along into the air is a typical 90 degree fitting, it may be changed to a
system, as well as a small amount of the lubricating oil straight or 45 degree fitting. For more information on
as vapor. how to help prevent discharge line freeze-ups, see
The duty cycle is the ratio of time the compressor Bendix Bulletins TCH-08-21 and TCH-08-22 (see
spends building air to the total engine running time. pages 31-33). Shorter discharge line lengths or
Air compressors are designed to build air (run “loaded”) insulation may be required in cold climates.
up to 25% of the time. Higher duty cycles cause The air dryer contains a filter that collects oil droplets,
conditions that affect air brake charging system and a desiccant bed that removes almost all of the
performance which may require additional remaining water vapor. The compressed air is then
maintenance. Factors that add to the duty cycle are: passed to the air brake service (supply) reservoir. The
air suspension, additional air accessories, use of an oil droplets and the water collected are automatically
undersized compressor, frequent stops, excessive purged when the governor reaches its “cut-out” setting.
leakage from fittings, connections, lines, chambers or For vehicles with accessories that are sensitive to small
valves, etc. amounts of oil, we recommended installation of a
The discharge line allows the air, water-vapor and Bendix® PuraGuard® system filter, designed to minimize
oil-vapor mixture to cool between the compressor and the amount of oil present.

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
Discharge Optional “Ping” Tank consists of an air compressor, governor, discharge line,
Line Air Dryer air dryer, and service reservoir.
Optional Bendix® PuraGuard®
System Filter or PuraGuard®
QC™ Oil Coalescing Filter

Compressor
Governor
(Governor plus Synchro valve Service Reservoir
for the Bendix® DuraFlo™ 596™ (Supply Reservoir)
Compressor)
Reservoir Drain

14
 Table A: Maintenance Schedule and Usage Guidelines
Regularly scheduled maintenance is the single most important factor in maintaining the air brake charging system.
Column 1 Column 2 Column 3 Column 4 Column 5
Recom- Recom- Acceptable
Typical Discharge mended mended Reservoir
Compressors Line Air Dryer Reservoir Oil Contents3
No. of Spec'd Cartridge Drain at Regular
Vehicle Used for: Axles I.D. Length Replacement1 Schedule2 Drain Interval

Low Air Use

Compressor with less than 15% duty 1/2 in. 6 ft.
cycle BASIC test
5 For oil carry-over acceptable
e.g. Line haul single trailer

Bendix® Tu-Flo® 550 air compressor

or control4 suggested Recom- range:
w/o air suspension, air over upgrades:
hydraulic brakes. less mended 3 oil units
5/8 in. 9 ft. per month.
Every 3 Every
Month - See
Compressor with up to 25% duty cycle Years
1/2 in. 9 ft. Max of appendix

Bendix® BA-921™ air compressor

e.g. Line haul single trailer 5 every 90 A.
with air suspension, or For oil carry-over
control4 suggested days
school bus. less upgrades:
5/8 in. 12 ft. For the
BASIC
High Air Use Test Kit:
Order
Compressor with up to 25% duty cycle Bendix
P/N
e.g. Double/triple trailer, open 5013711
Bendix® Tu-Flo® 750 air compressor

highway coach/RV, (most)

pick-up & delivery, yard or 1/2 in. 12 ft.
terminal jockey, off-highway, Every 2
8 For oil carry-over
construction, loggers, concrete control4 suggested
Years
or
mixer, dump truck, fire truck. upgrades:
less
5/8 in. 15 ft.
Bendix® BA-922™, or DuraFlo™ 596 air compressor

BASIC test
acceptable
range:
Every 5 oil units
Compressor with up to 25% duty cycle Month per month.
See
e.g. City transit bus, refuse, appendix
bulk unloaders, low boys, 5/8 in. 12 ft. A.
urban region coach, central
tire inflation. 12 Every
For oil carry-over Year
or control4 suggested
less upgrades:
3/4 in. 15 ft.

Footnotes:
1 With increased air demand the air dryer cartridge needs to be replaced more often. Note: Compressor and/or air dryer
2 Use the drain valves to slowly drain all reservoirs to zero psi. upgrades are recommended in cases
where duty cycle is greater than the
3 Allow the oil/water mixture to fully settle before measuring oil quantity. normal range (for the examples
4 To counter above normal temperatures at the air dryer inlet, (and resultant oil-vapor passing above).
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 For Bendix® Tu-Flo® 550 and 750
oil-vapor condenses and can be removed by the air dryer. Discharge line upgrades are not compressors, unloader service is
covered under warranty. Note: To help prevent discharge line freeze-ups, shorter discharge recommended every 250,000 miles.
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.

15
Air Brake Charging System Troubleshooting
How to use this guide:
Find the symptom(s) that you see, then move to the right to Look for:
find the possible causes (“What it may indicate”) and
remedies (“What you should do”).
Review the warranty policy before performing any intrusive Normal - Charging system is working within
compressor maintenance. Unloader or cylinder head gasket normal range.
replacement and resealing of the bottom cover plate are
usually permitted under warranty. Follow all standard safety
procedures when performing any maintenance. Check - Charging system needs further
investigation.

WARNING! Please READ and follow these instructions to 5. Following the vehicle manufacturer’s recommended
avoid personal injury or death: procedures, deactivate the electrical system in a manner
When working on or around a vehicle, the following general that safely removes all electrical power from the vehicle.
precautions should be observed at all times. 6. Never exceed manufacturer’s recommended pressures.
1. Park the vehicle on a level surface, apply the parking 7. Never connect or disconnect a hose or line containing
brakes, and always block the wheels. Always wear safety pressure; it may whip. Never remove a component or plug
glasses. unless you are certain all system pressure has been
2. Stop the engine and remove ignition key when working depleted.
under or around the vehicle. When working in the engine 8. Use only genuine Bendix® replacement parts, components
compartment, the engine should be shut off and the ignition and kits. Replacement hardware, tubing, hose, fittings, etc.
key should be removed. Where circumstances require that must be of equivalent size, type and strength as original
the engine be in operation, EXTREME CAUTION should equipment and be designed specifically for such
be used to prevent personal injury resulting from contact applications and systems.
with moving, rotating, leaking, heated or electrically charged 9. Components with stripped threads or damaged parts
components. should be replaced rather than repaired. Do not attempt
3. Do not attempt to install, remove, disassemble or assemble repairs requiring machining or welding unless specifically
a component until you have read and thoroughly stated and approved by the vehicle and component
understand the recommended procedures. Use only the manufacturer.
proper tools and observe all precautions pertaining to use 10. Prior to returning the vehicle to service, make certain all
of those tools. components and systems are restored to their proper
4. If the work is being performed on the vehicle’s air brake operating condition.
system, or any auxiliary pressurized air systems, make 11. For vehicles with Antilock Traction Control (ATC), the ATC
certain to drain the air pressure from all reservoirs before function must be disabled (ATC indicator lamp should be
beginning ANY work on the vehicle. If the vehicle is ON) prior to performing any vehicle maintenance where
equipped with an AD-IS™ air dryer system or a dryer one or more wheels on a drive axle are lifted off the ground
reservoir module, be sure to drain the purge reservoir. and moving.

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

1.0 Oil Test Card Not a valid test. Discontinue using this test.
Results Do not use this card test to diagnose

û
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
Bendix® page 28 for a flowchart and expanded
explanation of the checklist used when

ü
BASIC Test conducting the BASIC test.)

16
 Symptom: What it may indicate: What you should do:
2.0 Oil on the Engine and/or other accessories Find the source and repair. Return the vehicle
Outside of the leaking onto compressor. to service.
Compressor

2.1 Oil leaking at (a)Leak at the front or rear (fuel ð Repair or replace as necessary. If the
compressor / engine pump, etc.) mounting flange. mounting bolt torques are low, replace the
connections: 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.

2.2 Oil leaking (a)Excessive leak at head gasket. ð Go to Test 1 on page 26.
from compressor:
(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.

ð
(c)
(a)

Head
gasket
ð and rear
flange
gasket
(c) locations.

3.0 Oil at air dryer Air brake charging system functioning ð Air dryers remove water and oil from the
purge/exhaust or normally. air brake charging system.
surrounding area 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.

17
 Symptom: What it may indicate: What you should do:
4.0 Oil in Supply or Maintenance
Service Reservoir
(a) If air brake charging system ð Drain all air tanks and check vehicle at next
(air dryer installed)
(If a maintained Bendix® maintenance has not been service interval using the Bendix® BASIC
PuraGuard® system filter performed. test. See Table A on page 15, column 3
or Bendix® PuraGuard® That is, reservoir(s) have not been and 4, for recommended service schedule.
QC™ oil coalescing filter drained per the schedule in Table
is installed, call A on page 15, 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.
speak to a Tech Team
member.)
(b) If the vehicle maintenance has ð Drain all air tanks into Bendix® BASIC test
been performed as recom- cup (Bendix Air System Inspection Cup).
mended in Table A on page 15, If less than one unit of reservoir contents
some oil in the reservoirs is normal. is found, the vehicle can be returned to
service. Note: If more than one oil unit
of water (or a cloudy emulsion mixture)
(a) 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/
See Table A, on page 15,
for maintenance cloudy emulsion mixture) is present, use
schedule information. the BASIC cup chart on the label of the
cup to determine if the amount of oil found
Drain all air tanks (reservoirs)
is within the acceptable level.
into the Bendix® BASIC test
cup. (Bendix kit P/N 5013711). 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 15, column
3 for recommended air dryer cartridge
replacement schedule.

Duty cycle too high

(c) Air brake system leakage. ð Go to Test 2 on page 26.

(d) Compressor may be undersized for ð See Table A, column 1, on page 15 for
the application. recommended compressor sizes.
ð If the compressor is "too small" for
The duty cycle is the ratio of time the compressor spends the vehicle's role (for example, where a
building air to total engine running time. Air compressors vehicle's use has changed or service
are designed to build air (to "run loaded") up to 25% of the conditions exceed the original vehicle or
time. Higher duty cycles cause conditions that affect air engine OE spec's) then upgrade the
brake charging system performance which may require compressor. Note: The costs incurred (e.g.
additional maintenance. Factors that add to the duty cycle installing a larger capacity compressor,
are: air suspension, additional air accessories, use of an etc.) are not covered under original
undersized compressor, frequent stops, excessive leakage compressor warranty.
from fittings, connections, lines, chambers or valves, etc. ð If the compressor is correct for the
vehicle, go to Symptom 4.0 (e).

18
 Symptom: What it may indicate: What you should do:

4.0 Oil in Supply Temperature

or Service ð Check temperature as outlined in Test 3
Reservoir* (e) Air compressor discharge and/or on page 26. If temperatures are normal
(air dryer installed) air dryer inlet temperature too high. go to 4.0(h).
(continued)
ð Inspect coolant line. Replace as necessary
(f) Insufficient coolant flow. (I.D. is 1/2").

ð Inspect the coolant lines for kinks and

(e) (f) restrictions and fittings for restrictions.
Replace as necessary.

ð Verify coolant lines go from engine block

to compressor and back to the water pump.
Repair as necessary.
(g)

ð If discharge line is restricted or more than

Testing the temperature Inspecting the coolant hoses. 1/16" carbon build up is found, replace the
at the discharge fitting. discharge line. See Table A, column 2, on
(g) Restricted discharge line. page 15 for recommended size. Replace
as necessary.
(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
Kinked discharge line shown. 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.

Other
(h) Restricted air inlet (not enough air ð Check compressor air inlet line for
to compressor). restrictions, brittleness, soft or sagging
hose conditions etc. Repair as necessary.
(h) 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

Partly necessary (if possible, check the air filter
collapsed usage indicator).
inlet line
shown.

*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.
19
 Symptom: What it may indicate: What you should do:

4.0 Oil in Supply Other (cont.)

or Service
(i) Poorly filtered inlet air (poor air ð Check for leaking, damaged or defective
Reservoir*
quality to compressor). compressor air inlet components (e.g.
(air dryer installed)
induction line, fittings, gaskets, filter bodies,
(continued)
etc.). Repair inlet components as needed.
Note: Dirt ingestion will damage
compressor and is not covered under
Inspect the warranty.
engine air
cleaner.

(j) Governor malfunction or setting. ð Go to Test 4 on page 27.

(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
Crankcase Flooding be passing oil.
Consider installing a compressor bottom drain kit Replace compressor. If still under
(where available) in cases of chronic oil passing warranty, follow normal warranty process.
where all other operating conditions have been Note: After replacing a compressor,
investigated. Bendix compressors are designed to
residual oil may take a considerable period
have a 'dry' sump and the presence of excess oil in
the crankcase can lead to oil carryover. of time to be flushed from the air brake
system.

*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 Air brake system valves are required ð A small amount of oil does not affect SAE
valves (e.g. at to tolerate a light coating of oil. J2024** compliant valves.
exhaust, or seen
during servicing). 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 15). Return the vehicle to
service.

For oil-sensitive systems, see page 14.

** 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.

20
 Symptom: What it may indicate: What you should do:

6.0 Excessive oil A problem with engine or other engine ð See engine service manual.
consumption in accessory.
engine. The engine
service
manual has
more
information.

7.0 Oil present at Air brake charging system is ð Air dryers remove water and oil from the air
air dryer cartridge functioning normally. brake charging system. A small amount of
during oil is normal. Check that regular
maintenance. maintenance is being performed and that
the amount of oil in the air tanks
Oil shown (reservoirs) is within the acceptable range
leaking
from an air shown by the BASIC Test (see also column
dryer 5 of Table A on page 15). Replace the air
cartridge. dryer cartridge as needed and return the
vehicle to service.

8.0 Oil in ping tank Air brake charging system is ð Follow vehicle O.E. maintenance
or compressor dis- functioning normally. recommendation for these components.
charge aftercooler.

9.0 Air brake (a) Air brake charging system ð Using dash gauges, verify that the
charging system functioning normally. compressor builds air system pressure
seems slow to from 85-100 psi in 40 seconds or less with
build pressure. engine at full governed rpm. Return the
vehicle to service.

(b) Air brake system leakage. ð Go to Test 2 on page 26.

(c) Compressor may be undersized for ð See Table A, column 1, on page 15 for
the application. 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 ð Go to Test 6 on page 27.

malfunction.

(e) Damaged compressor head ð An air leak at the head gasket may indicate
gasket. 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).

21
 Symptom: What it may indicate: What you should do:

9.0 Air brake (f) Restricted discharge line. ð If discharge line is restricted:
charging system ð By more than 1/16" carbon build up,
seems slow to replace the discharge line (see Table A,
build pressure. column 2, on page 15 for recommended
(continued) size) and go to Test 3 on page 26.
ð By other restrictions (e.g. kinks).
Replace the discharge line. See Table A,
(f) column 2, on page 15 for recommended
size. Retest for air build. Return vehicle to
service or, if problem persists, go to 9.0(a).

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
Dash gauges. Kinked discharge line shown. 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.

(g) Restricted air inlet (not enough air ð Check compressor air inlet line for
to compressor). restrictions, brittleness, soft or sagging
(g) 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 ð Check for leaking, damaged or defective
quality to compressor). 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.

22
 Symptom: What it may indicate: What you should do:

10.0 Air charging (a) Governor malfunction*. ð Go to Test 4 on page 27.

system doesn’t
build air. (b) Restricted discharge line. ð See 9.0(f).

(c) Air dryer heater malfunction: ð Replace air dryer heater.

exhaust port frozen open.

(d) Compressor malfunction. ð Replace the compressor only after making

certain the preceding conditions do not
* Note: For the Bendix® DuraFlo™ 596 air compressor, not only exist.
the governor, but also the SV-1™ synchro valve used would
need to be tested. See Bulletin TCH-001-048.

11.0 Compressor (a) Restricted discharge line. ð If discharge line is restricted:

safety valve ð By more than 1/16" carbon build up,
releases air replace the discharge line (see Table A,
(Compressor column 2, on page 15 for recommended
builds too much size) and go to Test 3 on page 26.
air). ð By other restrictions (e.g. kinks).
Replace the discharge line. See Table A,
column 2, on page 15 for recommended
size.

ð The discharge line must maintain a

ð

constant slope down from the compressor

Damaged to the air dryer inlet fitting to avoid low
discharge points where ice may form and block the
line
shown. 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.

(b) Downstream air brake system ð Inspect air lines and verify check valves
check valves or lines may be are operating properly.
blocked or damaged.

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

(e) Compressor unloader mechanism ð Go to Test 6 on page 27.

malfunction.

(f) Governor malfunction. ð Go to Test 4 on page 27.

23
 Symptom: What it may indicate: What you should do:

12.0 Air dryer (a) Restriction between air dryer and ð Inspect delivery lines to reservoir for
safety valve reservoir. restrictions and repair as needed.
releases air.
(b) Air dryer safety valve malfunction. ð Verify relief pressure is at vehicle or
Air dryer component manufacturer specifications.
safety valve Replace if defective.
ð
(c) Air dryer maintenance not ð See Maintenance Schedule and Usage
performed. Guidelines (Table A, column 3, on page
15).

(d) Air dryer malfunction. ð Verify operation of air dryer. Follow vehicle
O.E. maintenance recommendations and
component Service Data information.
ê
ê
(e) Improper governor control line ð Go to Test 5 on page 27.
installation to the reservoir.
Technician removes
governor. (f) Governor malfunction. ð Go to Test 4 on page 27.

13.0 Reservoir (a) Reservoir safety valve malfunction. ð Verify relief pressure is at vehicle or
safety valve component manufacturer's specifications
releases air (typically 150 psi). Replace if defective.

(b) Governor malfunction. ð Go to Test 4 on page 27.

(c) Compressor unloader mechanism ð Go to Test 6 on page 27.

malfunction.

14.0 Air dryer (a) Air dryer malfunction. ð Verify operation of air dryer. Follow vehicle
doesn’t purge. O.E. maintenance recommendations.
(Never hear
exhaust from air (b) Governor malfunction. ð Go to Test 4 on page 27.
dryer.)
(c) Air brake system leakage. ð Go to Test 2 on page 26.

(d) Improper governor control line ð Go to Test 5 on page 27.

installation to the reservoir.

15.0 Compressor (a) Air brake charging system ð Available reservoir capacity may be
constantly cycles maintenance not performed. reduced by build up of water etc. Drain
(compressor and perform routine maintenance per
remains unloaded Table A, columns 3 & 4, on page 15.
for a very short
time.) (b) Compressor unloader mechanism ð Go to Test 6 on page 27.
malfunction.

(c) Air dryer purge valve or delivery ð Verify operation of air dryer. Follow vehicle
check valve malfunction. O.E. maintenance recommendations and
component Service Data information.

(d) Air brake system leakage. ð Go to Test 2 on page 26.

24
 Symptom: What it may indicate: What you should do:

16.0 Compressor (a) Compressor leaks air at ð Check for leaking, damaged or defective
leaks air connections or ports. compressor fittings, gaskets, etc. Repair
or replace as necessary.

(b) Compressor unloader mechanism ð Go to Test 6 on page 27.

malfunction.

(c) Damaged compressor head ð An air leak at the head gasket may indicate
gasket. a downstream restriction such as a freeze-
up or carbon blockage and/or could
Testing for leaks Head indicate a defective or missing safety
with soap solution. gasket valve. Find blockage (go to 9.0(f) for
ð location details.) and then replace the compressor.
Do not re-use the safety valve without
testing. See Symptom 12.0(a).

17.0 Compressor (a) Improperly installed plugs or ð Inspect for loose or over-torqued fittings.
leaks coolant coolant line 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 compressor head ð An air leak at the head gasket may indicate
gasket. 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).

(c) Porous compressor head casting. ð If casting porosity is detected, replace the
compressor.

18.0 Noisy (a) Damaged compressor. ð Replace the compressor.

compressor
(Multi-cylinder
compressors only)

Other Miscellaneous Areas to Consider

This guide attempts to cover most • Where a compressor does not have a
compressor system problems. Here are safety valve installed, if a partial or
some rare sources of problems not complete discharge line blockage has
covered in this guide: occurred, damage can occur to the
• Turbocharger leakage. Lubricating oil connecting rod bearings. Damage of this
from leaking turbocharger seals can enter kind may not be detected and could lead
the air compressor intake and give to compressor problems at a later date.
misleading symptoms.

25
 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.
LOOK
Observe the amount of weepage from the head gasket. FOR
If the oil is only around the cylinder head area, it is acceptable (return the WEEPAGE
vehicle to service), but, if the oil weepage extends down to the nameplate area
of the compressor, the gasket can be replaced.

Test 2: Air Brake System and Accessory Leakage

Inspect for air leaks when working on a vehicle and pedal in position.) Observe the dash gauges.
repair them promptly. If you see any noticeable decrease of the dash air
Park the vehicle on level ground and chock wheels. gauge readings (i.e. more than 4 psi, plus two psi
Build system pressure to governor cut-out and allow for each additional trailer) during either two minute
the pressure to stabilize for one minute. test, repair the leaks and repeat this test to confirm
Step 1: Observe the dash gauges for two additional that they have been repaired.
minutes without the service brakes applied. Air leaks can also be found in the charging system,
Step 2: Apply the service brakes and allow the parking brakes, and/or other components - inspect
pressure to stabilize. Continue holding for two and repair as necessary.
minutes (you may use a block of wood to hold the

Test 3: Air Compressor Discharge

Temperature and Air Dryer Inlet (* Note that only vehicles that have passed Test 2
Temperature* would be candidates for this test.)
Caution: The temperatures used in this test 4. Then, while maintaining max rpm and
are not normal vehicle conditions. pressure range, measure and record the
Above normal temperatures can cause oil (as surface temperature of the fittings:
vapor) to pass through the air dryer into the ð at the compressor discharge port. (T1).
air brake system. ð at the air dryer inlet fitting. (T2).
This test is run with the engine at normal Use a touch probe thermocouple for
operating temperature, with engine at max. rpm. measuring the temperature.
If available, a dyno may be used. 5. See table below.
1. Allow the compressor to build the air system 6. Retest before returning the vehicle to service.
pressure to governor cut-in.
2. Pump the brakes to bring the dash gauge
pressure to 90 psi. T1 T2
Compressor Air Dryer
3. Allow the compressor to build pressure from Discharge Inlet Action
95 to 105 psi gauge pressure and maintain Fitting Fitting
this pressure range by cycling the brakes for under under Temperatures are within
five (5) minutes. 360°F 200°F normal range for this test, check
other symptoms. Go to 4.0 (h).
T1
under over This could indicate a discharge
360°F 200°F line problem (e.g. restriction).
Call 1-800-AIR-BRAKE
T2 (1-800-247-2725)
and speak with our Tech Team.

over __ Compressor is running hot.

360°F Check coolant 4(f) and/or
Discharge Line discharge line 4(g).

26
 Tests (continued)
Test 4: Governor Malfunction
reservoir, service reservoir, or reservoir port
1. Inspect control lines to and from the governor of the D-2™ governor, verify cut-in and cut-
for restrictions (e.g. collapsed or kinked). out pressures are within vehicle OEM
Repair as necessary. specification.
2. Using a calibrated external gauge in the supply 3. If the governor is malfunctioning, replace it.

Test 5: Governor Control Line

1. Ensure that the governor control line from the 2. Perform proper reservoir drain intervals and
reservoir is located at or near the top of the air dryer cartridge maintenance per
reservoir. (This line, if located near the bottom Maintenance Schedule and Usage Guidelines
of the reservoir, can become blocked or (Table A on page 15).
restricted by the reservoir contents e.g. water 3. Return the vehicle to service.
or ice.)

Test 6: Compressor Unloader Leakage

Bendix ® Compressors: Park vehicle, chock off and charge the unloader port by allowing air
wheels, and follow all standard safety procedures. pressure to enter the hose and unload the
Remove the governor and install a fitting to the compressor. Shut off the air supply and observe
unloader port. Add a section of air hose (min 1ft the gauge. A steady reading indicates no leakage
long for a 1/2" diameter line) and a gauge to the at the unloader port, but a falling reading shows
fitting followed by a shut-off valve and an air that the unloader mechanism is leaking and needs
source (shop air or small air tank). Open the shut to be serviced.

27
 Appendix A: Information about the BASIC Test Kit (Bendix P/N 5013711)
Service writer records info - including days
the number of days since all air tanks
were drained - and fills out symptom Bendix® Air System Inspection Cup
checklist. Technician inspects items.
(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 YES Vehicle OK.

less than one Return vehicle to END TEST
unit of liquid? service.

NO

Is
there more
than one unit of: YES Cloudy emulsion mixture
• water, or
• cloudy emulsion
mixture?

NO, only oil.

Is this a Is this vehicle

YES, this is a high transit vehicle, bulk NO, this is a low air being re-tested (after
air use use vehicle. YES NO
unloader, or has more water, etc. was found
vehicle.
than 5 axles? last time?)

Find the point on the label Find the point on the label
where the number of oil units where the number of oil units Go to the
h meets the number of days* meets the number of days* Change air dryer
Hig
Low Advanced
since the vehicle's air tanks since the vehicle's air tanks cartridge**
Troubleshooting
were last drained. were last drained. Guide to find
Hig
h reason(s) for
presence of water Test for air
Is the Is the leakage Use Test 2:
point above point above Air Leakage
the HIGH Air Use the LOW Air Use END TEST
line on the NO line on the
cup? cup?
Low
NO Re-test with the
igh
H
YES Low BASIC Test after
YES 30 days***

Test for air

leakage
Use Test 2: END TEST
Air Leakage Vehicle OK.
Return vehicle to END TEST
service.

Does YES Repair leaks and * If the number of days since the air tanks were drained is
the vehicle have
return vehicle to END TEST
excessive air
service
unknown - use the 30 day line.
leakage?
** Note: Typical air dryer cartridge replacement schedule is every
NO 3 yrs/ 300K miles for low air use vehicles and every year/100K
NO (did not know miles for high air use vehicles.
Was when last
the number of drained) Re-test with the *** To get an accurate reading for the amount of oil collected
days since last BASIC Test after END TEST during a 30 day period, ask the customer not to drain the air
draining 30 days***
known? tanks before returning. (Note that 30-90 days is the
YES, number of days recommended air tank drain schedule for vehicles equipped
was known (30 - 90 days) with a Bendix air dryer that are properly maintained.) If, in cold
Replace the Compressor. If under warranty, follow standard weather conditions, the 30 day air tank drain schedule is longer
procedures. than the customer's usual draining interval, the customer must
If, after a compressor was already replaced, the vehicle fails the determine, based on its experience with the vehicle, whether to
Compressor
BASIC test again, do not replace the compressor**** - use the participate now, or wait for warmer weather. See the cold
Advanced Troubleshooting Guide to investigate the cause(s). weather tips in Bulletins TCH-008-21 and TCH-008-22 (included
on pages 31-33 of this document).
END TEST ****Note: After replacing a compressor, residual oil may take a
considerable period of time to be flushed from the air brake system.

28
 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

Customer’s Complaint Have you confirmed complaint?

è
(Please check all that apply)
“Relay valve q leaks oil / q malfunctions” . . . . . . . q no q yes* The Technician
“Dash valve q leaks oil / q malfunctions” . . . . . . . q no q yes* checks boxes for
The Service Writer q “Air dryer leaks oil” . . . . . . . . . . . . . . . . . . . . . . . q no q yes*
also checks off any any of the
q “Governor malfunction” . . . . . . . . . . . . . . . . . . . . q no q yes* complaints that
complaints that the q “Oil in gladhands” . . . . . . . . . . . . . . . . . . . . . . . . q no q yes*
customer makes to how much oil did you find? ________________________________ can be confirmed.
help the Technician q “Oil on ground or vehicle exterior” . . . . . . . . . . . q no q yes*
in investigating. amount described: ______________________________________
q “Short air dryer cartridge life”
replaces every: ______________ q miles, q kms, or q months
q “Oil in air tanks” amount described:_______________________ * Note: A confirmed com-
plaint above does NOT mean
We will measure amount currently found when we get to step B of the test. that the compressor must be
q “Excessive engine oil loss” amount described: ______________ replaced.
Is the engine leaking oil? . . . . . . . . . . . . . . . . . . . . . q no q yes* The full BASIC test below will
Is the compressor leaking oil? . . . . . . . . . . . . . . . . . q no q yes* investigate the facts.
q Other complaint:
______________________________________
q No customer complaint.

BASIC test starts here: STEP A - Select one: The Technician selects the air use
category for the vehicle. This
q This is a low air use vehicle: Line haul (single trailer) with 5 or less axles, or decided which of the two accep-
q This is a high air use vehicle: Garbage truck, transit bus, bulk unloader, or tance lines on the cup will be used
line haul with 6 or more axles. Then go to Step B. for the test below.

STEP B - Measure the Charging System Contents

For an accurate test, the
1. Park and chock vehicle on level ground. Drain the air system by contents of all the air tanks on
pumping the service brakes.
2. Completely drain ALL the air tanks into a single BASIC cup. the vehicle should be used.
3. If there is less than one unit of contents total, end the test now and
return the vehicle to service. Vehicle passes. Note for returning vehicles that are being
4. If more than one oil unit of water (or a cloudy emulsion mixture) retested after a water/cloudy emulsion
is found: mixture was found last time and the air
(a) Change the vehicle’s air dryer cartridge dryer cartridge replaced: If more than one
- see Footnote 1, Oil
Units oil unit of water or a cloudy emulsion mixture
(b) Conduct the 4 minute leakage test (Step D), is found again, stop the BASIC test and
(c) STOP the inspection, and check the vehicle consult the air dryer's Service Data sheet
again after 30 days - see Footnote 2. STOP troubleshooting section.
+ CK.
Otherwise, go to Step C.
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).

29
 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.

STEP C - How to Use the BASIC Test 1. Record days since air 2. Record amount
tanks were last drained. of oil found: 3. Action to
take
The Technician uses the chart (label) on the BASIC _________ days _________ units
test cup to help decide the action to take, based

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

Acceptance
BASIC Test Example Lines
Oil
An oil level of 4 units in a sixty-day period is within the Level
acceptance area (at or below the line) for both low
and high air use vehicles. Return the vehicle to service.
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) Sixty days since last air Decision point
acceptance line, the vehicle has passed the test. If tank draining
the point is above the line we go to the leakage test.
Air leakage is the number one
cause of compressors having
to pump excessive amounts of
STEP D - Air Brake System Leakage Test air, in turn run too hot and
Park the vehicle on level ground and chock wheels. Build system pressure to governor cut-out pass oil vapor along into the
and allow the pressure to stabilize for one minute. system. Here the Technician
1: Observe the dash gauges for two additional minutes without the service brakes applied. conducts a four-minute test to
2: Apply service brakes for two minutes (allow pressure to stabilize) and observe the dash see if leakage is a problem
gauges.
with the vehicle being tested.
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.
The Technician only reaches
Step E if the amount of oil
STEP E - If no air leakage was detected in Step D found, for the amount of time
since the air tanks were last
Replace the compressor.
drained exceeds the accep-
tance level, AND the vehicle
Note: If the compressor is within warranty period,
passes the four-minute
please follow standard warranty procedures. Attach
leakage test (no noticeable
the completed checklist to warranty claim.
leakage was detected).

30
 Appendix B

Technical Bulletin
Bulletin No.: TCH-008-021 Effective Date: 11/1/92 Page: 1 of 2

Subject: Air Brake System - Cold Weather Operation Tips

As the cold weather approaches, operators and 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 I.D. Min. Other Requirements

6.0-9.5 ft. ½ in. None
9.5-12 ft. ½ in. Last 3 feet, including fitting at the end of the
discharge line, must be insulated with ½ inch thick closed
cell polyethylene pipe insulation.
12-16 ft. 5/8 in. Last 3 feet, including 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.

31
 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 Service Data Sheet SD-08-2412

AD-4™ Air Dryer Service Data Sheet SD-08-2407
AD-2™ Air Dryer Service Data Sheet SD-08-2403
AD-IP™ Air Dryer Service Data Sheet SD-08-2414
AD-SP™ Air Dryer Service Data Sheet SD-08-2415
Trailer System-Guard™ Air Dryer Service Data Sheet SD-08-2416

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 Appendix B: Continued

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

Subject: Additional Cold Weather Operation Tips for the Air Brake System
Last year we published Bulletin PRO-08-21 which provided some guidelines for “winterizing” a vehicle
air brake system. Here are some additional suggestions for making cold weather vehicle operation
just a little more bearable.
Thawing Frozen Air Lines
The old saying; “Prevention is the best medicine” truly applies here! Each year this activity accounts
for an untold amount of unnecessary labor and component replacement. Here are some Do’s and
Don’ts for prevention and thawing.
Do’s
1. Do maintain freeze prevention devices to prevent road calls. Don’t let evaporators or injectors run
out of methanol alcohol or protection will be degraded. Check the air dryer for proper operation
and change the desiccant when needed.
2. Do thaw out frozen air lines and valves by placing the vehicle in a warmed building. This is the
only method for thawing that will not cause damage to the air system or its components.
3. Do use dummy hose couplings on the tractor and trailer.
4. Do check for sections of air line that could form water traps. Look for “drooping” lines.
Don’ts
1. Do not apply an open 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.

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