TM-9-2320-272-24-1
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; UNIT, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE MANUAL; VOLUME 1 OF 4
JUNE 1998
TM-9-2320-272-24-1 - Page 266 of 1015
TM 9-2320-272-24-1
COMPRESSED AIR AND BRAKE SYSTEM TROUBLESHOOTING INDEX
MALFUNCTION
NO.
MALFUNCTION
TROUBLESHOOTING
PROCEDURE
PAGE
3.
1.
2.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
PARKING BRAKE
Parking brake does not hold vehicle on grade . . . . . . . . . . . . . . . . . . . . . . . . . .
Parking brake drags, as indicated by smoking or burning smell. . . . . . . . . . . .
SERVICE BRAKES
Insufficient brakes (vehicle stopping distance too long, no apparent
air system failure with gauges at normal operating pressure,
warning buzzer not sounding) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vehicle pulls right or left when applying brakes . . . . . . . . . . . . . . . . . . . . . . . .
Vehicle rear brakes grab or drag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vehicle vibrates, chatters, or bounces when brakes are applied . . . . . . . . . . . .
Brakes squeal
...................................................
Warning buzzer sounds when brakes are applied (primary and secondary
gauge pressure drops below 55-65 psi (379-448 kPa). . . . . . . . . . . . . . . . . . . .
COMPRESSED AIR SUPPLY
No air pressure (warning buzzer sounding, air pressure not building to
normal operating range as indicated by gauges) . . . . . . . . . . . . . . . . . . . . . . .
Air pressure does not build to normal operating pressure
(above 80 psi (552 kPa)) according to gauges. . . . . . . . . . . . . . . . , . . . . . . . . .
Air pressure builds slowly (takes excessive amount of time to build to
100 psi (690kPa)
...............................................
Air pressure exceeds maximum (gauges show over 130 psi (896 kPa)),
safety valve opens to release pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Primary pressure gauge reads no pressure, low pressure, or builds to
normal operating pressure slowly. Secondary pressure gauge reads normal
(engine idling, brake pedal not applied). . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Secondary pressure gauge reads no pressure, low pressure, or builds to
normal operating pressure slowly. Primary pressure gauge reads normal
(engine idling, brake pedal not applied). . . . . . . . . . . . . . . . . . . . . . . . . , . . . .
Primary air system fails to maintain pressure (no major leaks, air can be
heard escaping into air intake stack, parking brake applied) . . . . . . . . . . . . .
Secondary air system fails to maintain pressure (no major leaks, air can be
heard escaping into air intake stack, parking brake applied) . . . . . . . . . . . . .
Warning buzzer fails to sound or fails to shut off on low pressure
(below 55-65 psi (379-448 kPa)), air pressure system operating normally. . . .
Spring brakes do not release (vehicle brakes grab or drag). . . . . . . . . . . . . . . .
Spring brakes do not set (gauges at normal operating pressures, air
exhausting not heard when parking brake applied). . . . . . . . . . . . . . . . . . . . .
AIR-OPERATED ACCESSORIES
All air-operated accessories do not operate (horn, windshield wipers,
windshield washers, transfer case controls), gauges at normal operating
pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cooling fan does not operate, engine temperature above 200°F (93°C) as
indicated by temperature gauge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Cooling fan does not stop running, engine temperature below normal
operating range (override bolt not installed) . . . . . . . . . . . . . . . . . . . . . . . . . .
Front wheel drive does not engage (front wheel drive lock-in switch
engaged and transfer case shift lever in HIGH position). . . . . . . . . . . . . . . . .
Horn does not work (gauges at normal operating pressure, warning buzzer
not sounding)
..................................................
2-179
2-179
2-180
2-194
2-196
2-196
2-196
2-196
2-197
2-200
2-200
2-200
2-202
2-206
2-208
2-208
2-210
2-210
2-212
2-213
2-213
2-214
2-214
2-218
2-178
Back to Top
