Air Inlet Port Air From Governor Unloader Port
air passageway is opened between the cylinder bore and the air inlet cavity in the cylinder head. As the piston moves from bottom dead center (BDC) to top dead center (TDC) air in the cylinder bore ows past the unseated unloader piston, into the cylinder head inlet cavity and out the inlet port. To prevent the air from owing back into the engine air induction system, an inlet check valve (ICV) is installed upstream of the air compressor inlet port. The location of the device and the way it is plumbed into the compressor air induction system is unique to the specic engine and the type of air induction (naturally aspirated or boosted air) the compressor uses. These air induction systems will be explained in further detail in the Air Induction section on page 4. On the piston down stroke (TDC to BDC) air ows in the reverse direction, from the inlet cavity past the unseated unloader piston and inlet reed valve, and into the cylinder bore.

LUBRICATION

The vehicle's engine provides a continuous supply of oil to the compressor. Oil is routed from the engine to the compressor's oil inlet. An oil passage in the crankshaft routes pressurized oil to the precision sleeve main bearings and to the connecting rod bearings. Spray lubrication of the cylinder bores, connecting rod wrist pin bushings, and ball type main bearings is obtained as oil is forced out around the crankshaft journals by engine oil pressure. Oil then falls to the bottom of the compressor crankcase and is returned to the engine through drain holes in the compressor mounting ange.
Unloader Piston Up & Unseated
Air in Pistons Shuttles Back and Forth from the Piston to the Cylinder Head and Inlet Port During Unloaded Mode FIGURE 8 - OPERATION - UNLOADED 3

AIR INDUCTION GENERAL

The Bendix BA-921 air compressor can be used both with air induction systems that are naturally aspirated (atmospheric air) and pressurized (turbocharged). The following section covers Caterpillar and Detroit Diesel engine air induction arrangements. See Figure 4, for typical anges used.

Head Bolt (4) Discharge Safety Valve Coolant In or Out

(One or other not used)

Discharge Port

CATERPILLAR

Caterpillar HD ACERT engines (C11, C13, C15 and C18) and MD ACERT engines (C7 and C9) are typically equipped with Bendix BA-921 compressors. These engines provide pressurized (turbocharged) air to the compressor's inlet port. Caterpillar recommends the use of an inlet check valve in the air induction system to prevent the air from the compressor being forced back into the engine air induction system when the compressor is operating in the "unloaded" condition (not building air). Because the compressor induction system is turbocharged, an additional air volume (reservoir) is required between the compressor inlet port and the inlet check valve to prevent excessive air pressure at the compressor inlet in the unloaded mode. Figures 10 and 11 show example of the different air induction systems used by Caterpillar to perform this function.
Governor Connection Unloader Cover Inlet Port
Coolant In or Out CYLINDER HEAD PORT IDENTIFICATION The cylinder head connection ports are identied with cast in numerals as follows: AIR IN 0 Compressed AIR OUT 2 Coolant IN or OUT 9 Governor Control 4 FIGURE 9 - TYPICAL BENDIX BA-921 COMPRESSOR CYLINDER HEAD
CATERPILLAR C7/C9 ENGINES
The Bendix BA-921 compressor in the C7/C9 air induction system (see Figure 10) receives its air from the engine's intake manifold (turbocharged). During the pumping condition (loaded mode), the air ows from the engine intake manifold through the inlet check valve and inlet line to the compressor inlet port. During the non-pumping condition (unloaded mode), the compressor cylinder pushes air back out of the inlet port to the inlet check valve. The ICV prevents the air from traveling beyond this point. Because the air is boosted (under pressure), it is important that the compressor inlet line is of sufcient length, strength and volume to minimize the build-up of air pressure in the inlet system. The air shuttles back and forth between the compressor cylinder bore and the ICV during this phase of the compressor operation.
expansion tank) prevents the air from traveling beyond this point. Because the air is boosted (under pressure), it is important that the compressor inlet line is of sufcient length, strength and volume to minimize the build-up of air pressure in the inlet system. The air shuttles back and forth between the compressor cylinder bore and the expansion tank during this phase of the compressor operation.

Inlet Port Inlet Line

CATERPILLAR C11, C13, C15 AND C18 ENGINES
The Bendix BA-921 compressor in the C11, C13, C15, and C18 air induction systems (see Figure 11) receives its air from the engine's intake manifold (turbocharged). During the pumping condition (loaded mode), the air ows from the engine intake manifold through the inlet check valve, expansion tank and inlet line to the compressor inlet port. During the non-pumping condition (unloaded mode), the compressor cylinder pushes air back out of the inlet port into the expansion tank. The ICV (at the end of the

Check the external oil supply line for kinks, bends, or restrictions to ow. Supply lines must be a minimum of 3/16 I.D. Refer to the tabulated technical data in the back of this manual for oil pressure minimum values. Check the exterior of the compressor for the presence of oil seepage and refer to the TROUBLESHOOTING section for appropriate tests and corrective action. Note: This is applicable only for Caterpillar engine installations. Detroit Diesel utilizes an internal oil feed design. No external oil supply line is used.

IMPORTANT NOTE

Replacement air governors must have a minimum cut-in pressure of 100psi. The cut-in pressure is the lowest system pressure registered in the gauges before the compressor resumes compressing air. Compressors with no signal line to the unloader port should have a vent cap (e.g. Bendix part number 222797) installed in the port. Under no circumstances should the port be plugged or left open.

OIL PASSING

All reciprocating compressors pass a minimal amount of oil. Air dyers will remove the majority of oil before it can enter the air brake system. For particularly oil sensitive systems, the Bendix PuraGuard system can be use in conjunction with a Bendix air dryer. If compressor oil passing is suspected, refer to the TROUBLESHOOTING section and TABLE A for the symptoms and corrective action to be taken. In addition, Bendix has developed the Bendix Air System Inspection Cup or BASIC kit to help substantiate suspected excessive oil passing. The steps to be followed when using the BASIC kit are presented in APPENDIX A at the end of the TROUBLESHOOTING section.

SERVICE TESTS

GENERAL
The following compressor operating and leakage tests need not be performed on a regular basis. These tests should be performed when it is suspected that leakage is substantially affecting compressor buildup performance, or when it is suspected that the compressor is cycling between the loaded (pumping) and unloaded (non-pumping) modes due to unloader leakage.
IN SERVICE OPERATING TESTS
Compressor Performance: Build-up Test This test is performed with the vehicle parked and the engine operating at maximum recommended governed speed. Fully charge the air system to governor cut out (air dryer purges). Pump the service brake pedal to lower the system air pressure below 80 psi using the dash gauges. As the air pressure builds back up, measure the time from when the dash gauge passes 85 psi to the time it passes 100 psi. The time should not exceed 40 seconds. If the vehicle exceeds 40 seconds, test for (and x) any air leaks, and then re- test the compressor performance. If the vehicle does not pass the test the second time, use the Advanced Troubleshooting Guide for Air Brake Compressors, starting on page 15 of this document to assist your investigation of the cause(s). Note: All new vehicles are certied using the FMVSS 121 test (paragraph S5.1.1) by the vehicle manufacturer, however the above test is a useful guide for in-service vehicles. Optional Comparative Performance Check It may be useful to also conduct the above test with the engine running at high idle (instead of maximum governed speed), and record the time taken to raise the system pressure a selected range (for example, from 90 to 120 psi, or from 100 to 120 psi, etc.) and record it in the vehicles maintenance les. Subsequent build-up times throughout the vehicles service life can then be compared to the rst one recorded. (Note: the 40 second guide in the test above does not apply to this build-up time.) If the performance degrades signicantly over time, you may use the Advanced Troubleshooting Guide for Air Brake Compressors, starting on page 15 of this document, to assist investigation of the cause(s). Note: When comparing build-up times, be sure to make an allowance for any air system modications which would cause longer times, such as adding air components or reservoirs. Always check for air system leakage.

CYLINDER HEAD

Check for cylinder head gasket air leakage. 1. With the engine running, lower air system pressure to 60 psi and apply a soap solution around the cylinder head. Check the gasket between the cylinder head and valve plate assembly and the inlet reed valve/gasket between the valve plate assembly and crankcase for air leakage. 2. No leakage is permitted. If leakage is detected replace the compressor or repair the cylinder head using a genuine Bendix maintenance kit available from an authorized Bendix parts outlet.
INLET, DISCHARGE & UNLOADER
In order to test the inlet and discharge valves and the unloader piston, it is necessary to have shop air pressure and an assortment of ttings. A soap solution is also required. 1. With the engine shut off, drain ALL air pressure from the vehicle. 2. Disconnect the inlet and discharge lines and remove the governor or its line or adapter tting. 3. Apply 120-130 psi shop air pressure to the unloader port and soap the inlet port. Leakage at the inlet port should not exceed 50 sccm. 4. Apply 120-130 psi shop air pressure to the discharge port and then apply and release air pressure to the inlet port. Soap the inlet port and note that leakage at the inlet port does not exceed 20 sccm. If excessive leakage is noted in Tests 3 or 4, replace or repair the compressor using genuine Bendix replacements or maintenance kits available from any authorized Bendix parts outlet. While it is possible to test for inlet, discharge, and unloader piston leakage, it may not be practical to do so. Inlet and discharge valve leakage can generally be detected by longer compressor build-up and recovery times. Compare current compressor build-up times with the last several recorded times. Make certain to test for air system leakage, as described under In Service Operating Tests, before making a determination that performance has been lost. Unloader leakage is generally exhibited by excessive compressor cycling between the loaded and unloaded condition. 1. With service and supply system leakage below the maximum allowable limits and the vehicle parked, bring system pressure to governor cut-out and allow the engine to idle.

COMPRESSOR REMOVAL & DISASSEMBLY
The following disassembly and assembly procedure is presented for reference purposes and presupposes that a rebuild or repair of the compressor is being undertaken. Several maintenance kits are available and the instructions provided with these parts and kits should be followed in lieu of the instructions presented here.
MAINTENANCE KITS & SERVICE PARTS
Cylinder Head Gasket Kit..5008558 Unloader Kit...5008557 Governor Adapter Kit...5008561 Compressor Seal Kit (crankcase)..5008559 Components and kits for Caterpillar Engines CAT C7/C9 Inlet Check Valve..801580 CAT C11/C13/C15/C18 Inlet Check Valve.801592 CAT C7/C9 Engine Seal Kit..5012367 CAT C11/C13/C15/C18 Engine Seal Kit..5012369 CAT ST-4 Discharge Safety Valve (7/8"-14 thrd.).801116 Components and kits for DDC Engines DDC Inlet Check Valve..802192 DDC Series 60 Engine Seal Kit...5012371 DDC ST-4 Discharge Safety Valve (M16-1.5 thrd.).800534
IMPORTANT! PLEASE READ AND FOLLOW THESE INSTRUCTIONS TO AVOID PERSONAL INJURY OR DEATH:
When working on or around a vehicle, the following general precautions should be observed at all times: 1. Park the vehicle on a level surface, apply the parking brakes, and always block the wheels. Always wear safety glasses. Where specically directed, the parking brakes may have to be released, and/or spring brakes caged, and this will require that the vehicle be prevented from moving by other means for the duration of these tests/procedures. 2. Stop the engine and remove ignition key when working under or around the vehicle. When working in the engine compartment, the engine should be shut off and the ignition key should be removed. Where circumstances require that the engine be in operation, EXTREME CAUTION should
1 Head Cap Screws (4) (include washers) 4 Unloader Cover 5 Unloader Cover Gasket 12 ST-4 Safety Valve
2 Unloader Cover Cap Screws (2) 3 Unloader Cover Splash Shield 6 Unloader Balance Piston 7 O-Ring 8 Spring 9 O-Ring 10 Unloader Piston 11 O-Ring

13 Cylinder Head

Alignment Bushings

lines. Do not use marking methods such as chalk that can be wiped off or obliterated during rebuilding. Prior to disassembly make certain that the appropriate kits and or replacement parts are available. Refer to Figure 13 during the entire disassembly and assembly procedure. What follows is a description of a complete disassembly, actual maintenance may only need to include portions of these instructions.
1. Remove the discharge safety valve (12) from the cylinder head (13). 2. To restrain the spring force exerted by balance piston spring (8) of the unloader assembly, hold the unloader cover (4) in place while removing the two unloader cover cap screws (2) and spray shield (3). Carefully release the hold on the unloader cover until the spring force is relaxed, then remove the unloader cover. 3. Remove the unloader cover gasket (5). 4. Remove the balance piston (6), its spring (8) and the unloader piston (10) along with its o-rings (7, 9 & 11) from the cylinder head (13). 5. Remove the four hex head bolts (1) from the cylinder head. 6. Gently tap the cylinder head, cooling plate (15) and valve plate assembly (16) with a soft mallet to break the gasket seal between the valve plate assembly and the crankcase (21). Lift the cylinder head with cooling plate and valve plate assembly off the crankcase. 7. Remove the metal inlet reed valve/gasket (17). 8. Gently tap the cylinder head, cooling plate and valve plate assembly with a soft mallet to break the gasket seals. Then separate the cylinder head from the cooling plate (15) and valve plate assembly and remove the two gaskets (14) between them.

CRANKCASE COVER

1. Remove the four crankcase cover cap screws (29) securing the crankcase cover (28) to the crankcase (21). Using a soft mallet, gently tap the crankcase cover to break the gasket seal. Remove the crankcase cover gasket (27). 2. In the case of the Caterpillar C11 and C13 engine application, the BA-921 compressor utilizes an oil jet that sprays oil under the piston for purposes of cooling. This oil jet is part of a special crankcase cover that is used strictly on the BA-921 compressor for the C11 and C13 engine installation (Figure 11). Refer to section OPERATION Lubrication for description of the system. To disassemble, follow the instructions below.
PREPARATION FOR DISASSEMBLY
Remove the balance of road dirt and grease from the exterior of the compressor with a cleaning solvent. If a rear end cover or end cover adapter is used on the compressor being worked on, mark it in relation to the crankcase. It is recommended, but not specically necessary, to mark the relationships of the cylinder head (13), cooling plate (15), valve plate assembly (16), and crankcase (21). A convenient method to indicate the above relationships is to use a metal scribe to mark the parts with numbers or
a. Remove the oil supply line from the engine at the inlet to the special crankcase cover. b. Remove the metal oil supply tube at the compressor oil supply port and at the outlet tting of the special crankcase cover. NOTE: Mark position of the special crankcase cover. It must be re-installed with the same orientation to assure proper operation of the oil jet. c. Remove the four crankcase cover cap screws securing the special crankcase cover to the crankcase. Using a soft mallet, gently tap the crankcase cover to break the gasket seal. Remove the crankcase cover gasket (27).

not recommended. Secure the compressor on the engine and tighten the mounting bolts per Engine Manufacturers recommended torque requirements. 2. Install any supporting brackets on the compressor in the same position(s) noted and marked during removal. If a rear support bracket was on the original installation, hand tighten the bolts on both ends before torquing the bolts. Note: It is important that the rear support bracket is ush to both surfaces before the bolts are torqued. 3. Inspect all air, oil, and coolant lines and ttings before reconnecting them to the compressor. Make certain o-ring seals are in good or new condition, the threads are clean and the ttings are free of corrosion. Replace as necessary. 4. Install the discharge, inlet, coolant and governor adapter ttings, if applicable, in the same position on the compressor noted and marked during disassembly. See the Torque Specications for various tting sizes and types of thread at the rear of this manual. Tighten all hose clamps. 5. Before returning the vehicle to service, perform the Operation and Leakage Tests specied in this manual. Pay particular attention to all lines and hoses disconnected during the maintenance and check for air, oil, and coolant leaks at compressor connections. Also check for noisy operation.
TESTING THE REBUILT COMPRESSOR
In order to properly test a compressor under operating conditions, a test rack for correct mounting, cooling, lubricating, and driving the compressor is necessary. Such tests are not compulsory if the unit has been carefully rebuilt by an experienced person. A compressor efciency or build-up test can be run which is not too difcult. An engine lubricated compressor must be connected to an oil supply line of at least 15psi pressure during the test and an oil return line must be installed to keep the crankcase drained. Connect to the compressor discharge port, a reservoir with a volume of 1500 cubic inches, including the volume of the connecting line. With the compressor operating at 2100 RPM, the time required to raise the reservoir(s) pressure from 85 psi to 100 psi should not exceed 5 seconds. During this test, the compressor should be checked for gasket leakage and noisy operation, as well as unloader operation and leakage. If the compressor functions as indicated, reinstall on the vehicle connecting all lines as marked in the disassembly procedure.

INSTALLING THE COMPRESSOR
1. Install the appropriate gasket or o-ring on the front ange of the compressor. Make certain oil supply or return holes in the gasket are properly aligned with the compressor and engine. On the Detroit Diesel S60 engine installations, an additional o-ring is required to seal the oil feed passageway between the compressor and engine gear case cover. Gasket sealants are
BA-921 COMPRESSOR SPECIFICATIONS
Typical weight... 37 lbs. Number of cylinders... 1 Bore Diameter.. 3.622 in. (92 mm) Stroke.. 2.126 in. (54 mm) Calculated displacement at 1250 RPM.. 15.8 CFM Flow Capacity @ 1800 RPM & 120 PSI. 11.6 CFM Flow Capacity @ 3000 RPM & 120 PSI. 16.5 CFM Approximate horsepower required: Loaded 1800 RPM at 120 PSIG.. 4.6 HP Unloaded 1800 RPM... 0.8 HP Minimum coolant ow at maximum RPM. 2.5 Gals./Min. Maximum inlet air temperature.. 250F Maximum discharge air temperature.. 400F Minimum oil pressure required.. 15 PSI Minimum oil-supply line size.. 3/16" I.D. Minimum unloader-line size.. 3/16" I.D. Minimum Governor Cut-out Pressure.. 120 PSI

TORQUE SPECIFICATIONS

Assembly Torques in inch pounds (in. Ibs.) M8x1.25-6g Cylinder Head.. 265-292 In. Lbs. (30-33 Nm) M5x0.75-6g Unloader Cap.. 62-71 In. Lbs. (7-8 Nm) M8x1.25-6g Governor Adapter. 195-213 In. Lbs. (22-24 Nm) M8x1.25-6g Rear End Cover.. 195-213 In. Lbs. (22-24 Nm) M6x1.00-6g Crankcase Cover. 62-71 In. Lbs. (7-8 Nm) Inlet Port Fittings 1 3/16"-12 UN-2B (Aluminum Cylinder Head) straight tting.. 841-925 In. Lbs. (95-104 Nm) adjustable (w/ jam nut). 597-655 In. Lbs. (67-74 Nm) M27x2-6g (Cast Iron Cylinder Head). 885-980 In. Lbs. (100-111 Nm) Discharge Port Fittings 7/8"-14 UNF-2B (Aluminum Cylinder Head) straight tting... 509-553 In. Lbs. (57-62 Nm) adjustable (w/ jam nut). 354-389 In. Lbs. (40-44 Nm) M22 x 1.5-6g (Cast Iron Cylinder Head) 531-575 In. Lbs. (60-65 Nm) Water Port Fittings 3/4"-16 UNF-2B (Aluminum Cylinder Head) straight tting... 265-292 In. Lbs. (30-33 Nm) adjustable (w/ jam nut). 248-274 In. Lbs. (28-31 Nm) M18 x 1.5-6g (Cast Iron Cyliner Head). 354-395 In. Lbs. (40-45 Nm) Unloader Port Fittings 1/8"-27 NPT...2 - 3 TFFT1 M10 x 1.5-6g... 120-145 In. Lbs. (14-16 Nm) Safety Valve Port 7/8"-14 UNF-2B. 230-257 In. Lbs. (26-29 Nm) M16x1.5-6H.. 230-257 In. Lbs. (26-29 Nm) Oil Port 7/16"-16 UNF.. 150-170 In. Lbs. (17-19 Nm) Special Attachments Cat C11/C13 Engine Crankcase Cover w/ Oil Jet and Associated Hardware (Figure 14) 1) Crankcase Cover (In/Out) Oil Fittings 7/16"-16 UNF. 150-170 In. Lbs. (17-19 Nm) 2) Compressor Oil Supply Fitting 7/16"-16 UNF. 150-170 In. Lbs. (17-19 Nm) 3) Metal Tube (Tube Ends) 7/16"-16 UNF.. 130-150 In. Lbs. (16-17.5 Nm) Option: Run ttings down nger tight. Tighten to turns.
Note: TFFT = Turns From Finger Tight
Advanced Troubleshooting Guide for Air Brake Compressors
Symptom Air Air brake charging system: Slow build (9.0)..23 - 24 Doesnt build air (10.0)..25 Air dryer: Doesnt purge (14.0).26 Safety valve releases air (12.0).26 Compressor: Constantly cycles (15.0)..26 Leaks air (16.0)..27 Safety valve releases air (11.0).25 Noisy (18.0)..27 Reservoir: Safety valve releases air (13.0).26 Page Number Symptom Coolant Compressor leaks coolant (17.0).. 27 Engine Oil consumption (6.0).. 23 Oil Oil Test Card results (1.0).. 18 Oil is present: On the outside of the compressor (2.0). 19 At the air dryer purge/exhaust or surrounding area (3.0).. 19 In the supply reservoir (4.0). 20 - 22 At the valves (5.0).. 22 At air dryer cartridge (7.0).. 23 In the ping tank or compressor discharge aftercooler (8.0).. 23 Page Number

The Air Brake Charging System supplies the
Discharge Line Optional Ping Tank Air Dryer compressed air for the braking system as well as other air accessories for the vehicle. The system usually consists of an air compressor, governor, discharge line, air dryer, and service reservoir. Optional Bendix PuraGuard System Filter or PuraGuard QC Oil Coalescing Filter

Compressor Governor

(Governor plus Synchro valve for the Bendix DuraFlo 596 Compressor) Service Reservoir

(Supply Reservoir)

Reservoir Drain
Table A: Maintenance Schedule and Usage Guidelines
Regularly scheduled maintenance is the single most important factor in maintaining the air brake charging
Column 1 Typical Compressors Spec'd

(See footnote 7)

Column 2 Discharge Line I.D. Length

Vehicle Used for:

Low Air Use
Compressor with less than 15% duty cycle

No. of Axles

Column 3 Recommended Air Dryer Cartridge Replacement1
Column 4 Recommended Reservoir Drain Schedule2
Column 5 Acceptable Reservoir Oil Contents3 at Regular Drain Interval

1/2 in.

Bendix Tu-Flo 550 air compressor
e.g. Line haul single trailer w/o air suspension, air over hydraulic brakes.
Compressor with up to 25% duty cycle

5 or less

For oil carry-over control4 suggested upgrades:

5/8 in. 1/2 in.

9 ft. 9 ft.

Every 3 Years

e.g. Line haul single trailer with air suspension, school bus.
Bendix BA-921 air compressor
Recommended Every Month Max of every 90 days
BASIC test acceptable range: 3 oil units per month. See appendix A.

5/8 in.

12 ft.

High Air Use

Bendix Tu-Flo 750 air compressor Compressor with up to 25% duty cycle
e.g. Double/triple trailer, open highway coach/RV, (most) pick-up & delivery, yard or terminal jockey, off-highway, construction, loggers, concrete mixer, dump truck, re truck.
For the BASIC Test Kit: Order Bendix P/N 5013711
12 ft. Every 2 Years BASIC test acceptable range: 5 oil units per month. See appendix A.

8 or less

Bendix BA-922, or DuraFlo 596 air compressor

15 ft.

Every Month 3/4 in. 12 ft. Every Year
e.g. City transit bus, refuse, bulk unloaders, low boys, urban region coach, central tire ination.

12 or less

Footnotes: 1. With increased air demand the air dryer cartridge needs to be replaced more often. 2. Use the drain valves to slowly drain all reservoirs to zero psi. 3. Allow the oil/water mixture to fully settle before measuring oil quantity. 4. To counter above normal temperatures at the air dryer inlet, (and resultant oil-vapor passing upstream in the air system) replace the discharge line with one of a larger diameter and/or longer length. This helps reduce the air's temperature. If sufcient cooling occurs, the oil-vapor condenses and can be removed by the air dryer. Discharge line upgrades are not covered under warranty. Note: To help prevent discharge line freeze-ups, shorter discharge line lengths or insulation may be required in cold climates. (See Bendix

Bulletins TCH-08-21 and TCH-08-22, included in Appendix B, for more information.) 5. For certain vehicles/applications, where turbo-charged inlet air is used, a smaller size compressor may be permissible. 6. Note: Compressor and/or air dryer upgrades are recommended in cases where duty cycle is greater than the normal range (for the examples above). 7. For correct compressor upgrades consult Bendix - Please note that because a compressor is listed in the same area of the chart does not necessarily mean that it would be a suitable candidate for upgrade purposes.
For Bendix Tu-Flo 550 and 750 compressors, unloader service is recommended every 250,000 miles.
Air Brake Charging System Troubleshooting
How to use this guide: Find the symptom(s) that you see, then move to the right to nd the possible causes (What it may indicate) and remedies (What you should do). Review the warranty policy before performing any intrusive compressor maintenance. Unloader or cylinder head gasket replacement and resealing of the bottom cover plate are usually permitted under warranty. Follow all standard safety procedures when performing any maintenance. Look for: Normal - Charging system is working within normal range.
Check - Charging system needs further investigation.
WARNING! Please READ and follow these instructions to
avoid personal injury or death: When working on or around a vehicle, the following general precautions should be observed at all times. 1. Park the vehicle on a level surface, apply the parking brakes, and always block the wheels. Always wear safety glasses. 2. Stop the engine and remove ignition key when working under or around the vehicle. When working in the engine compartment, the engine should be shut off and the ignition key should be removed. Where circumstances require that the engine be in operation, EXTREME CAUTION should be used to prevent personal injury resulting from contact with moving, rotating, leaking, heated or electrically charged components. 3. Do not attempt to install, remove, disassemble or assemble a component until you have read and thoroughly understand the recommended procedures. Use only the proper tools and observe all precautions pertaining to use of those tools. 4. If the work is being performed on the vehicles air brake system, or any auxiliary pressurized air systems, make certain to drain the air pressure from all reservoirs before beginning ANY work on the vehicle. If the vehicle is equipped with an AD-IS air dryer system or a dryer reservoir module, be sure to drain the purge reservoir.

Crankcase Flooding Consider installing a compressor bottom drain kit (where available) in cases of chronic oil passing where all other operating conditions have been investigated. Bendix compressors are designed to have a 'dry' sump and the presence of excess oil in the crankcase can lead to oil carryover.
5.0 Oil present at valves (e.g. at exhaust, or seen during servicing).
Air brake system valves are required to tolerate a light coating of oil.
A small amount of oil does not affect SAE J2024** compliant valves. Check that regular maintenance is being performed and that the amount of oil in the air tanks (reservoirs) is within the acceptable range shown on the Bendix BASIC test cup (see also column 5 of Table A on page 17). Return the vehicle to service. For oil-sensitive systems, see page 16.
** 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.
6.0 Excessive oil consumption in engine.
A problem with engine or other engine accessory.
The engine service manual has more information.
See engine service manual.
7.0 Oil present at air dryer cartridge during maintenance.
Air brake charging system is functioning normally.
Oil shown leaking from an air dryer cartridge.
Air dryers remove water and oil from the air brake charging system. A small amount of oil is normal. Check that regular maintenance is being performed and that the amount of oil in the air tanks (reservoirs) is within the acceptable range shown by the BASIC test (see also column 5 of Table A on page 17). Replace the air dryer cartridge as needed and return the vehicle to service. Follow vehicle O.E. maintenance recommendation for these components.
8.0 Oil in ping tank or compressor discharge aftercooler.
9.0 Air brake charging system seems slow to build pressure.
(a) Air brake charging system functioning normally.
Using dash gauges, verify that the compressor builds air system pressure from 85-100 psi in 40 seconds or less with engine at full governed rpm. Return the vehicle to service. Go to Test 2 on page 28. See Table A, column 1, on page 17 for some typical compressor applications. If the compressor is "too small" for the vehicle's role, for example, where a vehicle's use has changed, then upgrade the compressor. Note: The costs incurred (e.g. installing a larger capacity compressor, etc.) are not covered under original compressor warranty. Go to Test 6 on page 29.
(b) Air brake system leakage. (c) Compressor may be undersized for the application.
(d) Compressor unloader mechanism malfunction. (e) Damaged compressor head gasket.
An air leak at the head gasket may indicate a downstream restriction such as a freeze-up or carbon blockage and/or could indicate a defective or missing safety valve. Find blockage (go to 9.0(f) for details) and then replace the compressor. Do not reuse the safety valve without testing. See Symptom 12.0(a).

Go to Test 4 on page 29. See 9.0(f). Replace air dryer heater.
* Note: For the Bendix DuraFlo 596 air compressor, not only the governor, but also the SV-1 synchro valve used would need to be tested. See Bulletin TCH-001-048.
Replace the compressor only after making certain the preceding conditions do not exist.
11.0 Compressor safety valve releases air (Compressor builds too much air).
(a) Restricted discharge line.
If discharge line is restricted: By more than 1/16" carbon build-up, replace the discharge line (see Table A, column 2, on page 17 for recommended size) and go to Test 3 on page 28. By other restrictions (e.g. kinks). Replace the discharge line. See Table A, column 2, on page 17 for recommended size. The discharge line must maintain a constant slope down from the compressor to the air dryer inlet tting to avoid low points where ice may form and block the ow. If, instead, ice blockages occur at the air dryer inlet, insulation may be added here, or if the inlet tting is a typical 90 degree tting, it may be changed to a straight or 45 degree tting. For more information on how to help prevent discharge line freezeups, see Bendix Bulletins TCH-08-21 and TCH-08-22 (Appendix B). Shorter discharge line lengths or insulation may be required in cold climates. Inspect air lines and verify check valves are operating properly.
Damaged discharge line shown.
(b) Downstream air brake system check valves or lines may be blocked or damaged. (c) Air dryer lines incorrectly installed.
Ensure discharge line is installed into the inlet of the air dryer and delivery is routed to the service reservoir. Verify relief pressure is 250 psi. Replace if defective. Go to Test 6 on page 29.
(d) Compressor safety valve malfunction. (e) Compressor unloader mechanism malfunction. (f) Governor malfunction.

Go to Test 4 on page 29.

12.0 Air dryer safety valve releases air. Air dryer safety valve
(a) Restriction between air dryer and reservoir. (b) Air dryer safety valve malfunction.
Inspect delivery lines to reservoir for restrictions and repair as needed. Verify relief pressure is at vehicle or component manufacturer specications. Replace if defective. See Maintenance Schedule and Usage Guidelines (Table A, column 3, on page 17). Verify operation of air dryer. Follow vehicle O.E. maintenance recommendations and component Service Data information. Go to Test 5 on page 29.
(c) Air dryer maintenance not performed.
(d) Air dryer malfunction.
(e) Improper governor control line installation to the reservoir.
Technician removes governor.
(f) Governor malfunction. (a) Reservoir safety valve malfunction.

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