TM-9-2320-272-23-1

TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)

TECHNICAL MANUAL; FIELD MAINTENANCE MANUAL; VOLUME 1 OF 5

SEPTEMBER 2012

TM-9-2320-272-23-1 - Page 1062 of 1313

FIELD MAINTENANCE

VEHICLE VIBRATES, CHATTERS, OR BOUNCES WHEN BRAKES ARE APPLIED

INITIAL SETUP:

Tools and Special Tools

Tool Kit, General Mechanic's: Automotive

(Volume 5, WP

0826, Table 1, Item 56)

Gauge, Pressure

(Volume 5, WP

0826, Table 1, Item 19)

Test Set, Electronic Systems

(Volume 5, WP

0826, Table 1, Item 51)

Personnel Required

(2)

References

Point to Point Schematics

References (cont.)

WP

0120

WP

0122

Volume 5, WP

0805

Equipment Condition

Vehicle parked and engine shut down.

(TM

9-2320-272-10)

TROUBLESHOOTING PROCEDURE

VEHICLE VIBRATES, CHATTERS, OR BOUNCES WHEN BRAKES ARE APPLIED

NOTE

Conduct these malfunction tests if vehicle vibrates, chatters or bounces when brakes are

applied. This procedure will check for faulty or damaged rear brake system mechanism or

improper air supply pressure to rear brake chambers.

STEP

1.

ARE REAR SERVICE BRAKES LOCKING?

a.

Visually inspect rear service brakes for evidence of locking.

b.

Start engine and drive vehicle under normal conditions.

c.

In a safe test area, bring vehicle to a hard, sudden stop.

d.

Inspect rear wheels for excessive heat on wheel and drum.

e.

Inspect for smoke or skid marks.

CONDITION/INDICATION

ARE REAR SERVICE BRAKES LOCKING?

DECISION

YES - Perform Vehicle Rear Brakes Grab Or Drag troubleshooting (WP

0122).

NO - Go to Step (2).

TM 9-2320-272-23-1

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