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 1042 of 1313

INSUFFICIENT BRAKES (VEHICLE STOPPING DISTANCE TOO LONG, NO APPARENT AIR SYSTEM

FAILURE WITH GAUGES AT NORMAL OPERATING PRESSURE, WARNING BUZZER NOT SOUNDING) -

Continued

d.

Disconnect air line from secondary relay valve supply port (Volume 3, WP

0457). Refer to point to point

schematics.

e.

Connect pressure gauge to disconnected air supply line.

f.

Assistant starts engine and runs to build air supply to normal operating pressure.

g.

Assistant fully applies and holds service brakes.

h.

Monitor air pressure on pressure gauge.

i.

Pressure gauge should read 90 to 130 psi.

CONDITION/INDICATION

IS THERE PROPER AIR PRESSURE IN SUPPLY LINE FROM SECONDARY AIR TANK TO RELAY VALVE?

DECISION

NO - Replace damaged air line from primary air tank to secondary relay valve (Volume 5, WP

0805). Go to

Step

(30) to verify problem is solved.

YES - Replace secondary relay valve (Volume 3, WP

0457). Go to Step (30) to verify problem is solved.

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