TM 5-3805-254-20-1
ORGANIZATIONAL TROUBLESHOOTING - CONTINUED
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
68.
REAR BRAKES DO NOT WORK.
WARNING
Safety goggles must be worn when working with air lines to prevent personal injury.
Ensure that vehicle is on level ground and that rear wheels are chocked to prevent vehicle from moving or
severe injury to personnel may result.
NOTE
Check AIR PRESSURE gage for air pressure between 90 and 130 psi. If specified air pressure is not
present, start engine and check that air pressure in air system is between 90 and 130 psi (TM 5-3805-254-
10). Shut down engine (TM 5-3805-254-10).
Step 1.
Chock rear wheels of truck. Check rear airbrake chambers (1) for proper operation as follows: have
assistant push in PARKING BRAKE knob (2) to release parking brakes. Look at position of push
rod (3) and slack adjuster (4), and have assistant press down brake pedal (5). When push rod (3)
is out of airbrake chamber (1), brake is engaged. Have assistant release brake pedal (5), when
push rod (3) is in toward airbrake chamber (1), brake is disengaged.
a. If push rod (3) and slack adjuster (4) are not moving, go to step 2.
b. If push rod (3) and slack adjuster (4) are moving, go to step 11.
Step 2.
Check rear airbrake chambers (1) for air pressure as follows: using 3/4-inch and 5/8-inch open-end
wrenches, loosen service brake airhose fitting (6) six turns. Have assistant press down brake pedal
(5), and listen for hissing noise, release brake pedal (5).
a. If hissing noise is heard, defective airbrake chamber (1) must be replaced. Notify
Direct Support Maintenance.
b. If hissing noise is not heard, tighten service brake airhose fitting (6), using 3/4-inch and
5/8-inch open-end wrenches, go to step 3.
Step 3.
Check rear relay valve (7) for output air pressure as follows: using 7/8-inch open-end wrench,
loosen output hose fitting (8) six turns. Have assistant press down brake pedal (5), listen for hissing
noise at output hose fitting (8), release brake pedal (5).
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