TM-9-2320-285-24-2

TRUCK TRACTOR, YARD TYPE, 43,500 LB GVW, DED, 4X2, ARMY MODEL M878A1

TECHNICAL MANUAL; ORGANIZATIONAL, DIRECT SUPPORT AND GENERAL SUPPORT MAINTENANCE MANUAL

OCTOBER 1985

TM-9-2320-285-24-2 - Page 160 of 698

TM 9-2320-285-24-2

3-21.

TREADLE VALVE AND BRAKE CONTROLS TROUBLESHOOTING

MALFUNCTION

TEST OR INSPECTION

CORRECTIVE ACTION

1

.

RAPID PRESSURE DROP AFTER ENGINE IS SHUT DOWN (BRAKES RELEASED)

Step 1.

Check automatic drain valve at air supply reservoir for air exhaust.

a

.

If moderate to severe exhaust of air is observed, repair automatic drain valve (para 3-24e).

b

.

If constant slight exhaust of air is observed, proceed to step 2 below.

Step 2.

Check treadle valve (para 3-23), air compressor governor (para 2-52d), air reservoirs (para 2-51b),

safety valve (para 2-51b), and one way check valve (para 2-51b) for air leaks.

c.

If a component is leaking air, repair or replace (para 3-23, 2-52d, or 2-51b).

d

.

If components are not leaking air, replace air compressor discharge valves (para 3-25b).

2

.

RAPID PRESSURE DROP AFTER ENGINE IS SHUT DOWN (BRAKES APPLIED)

Check shift lockout air cylinder, brake air chambers, treadle valves, quick release valves, relay valve, ratio

reducing valve, and tractor protection valves for air leaks.

a

.

If a component is leaking air, repair or replace (para 2-41h(1), 2-51d(1), 2-51d(2), 3-23, 3-24b, 3-24g

, 3-24f, or 3-24h).

b

.

If components are not leaking air, troubleshoot AIR PRESS gage (para 2-83).

3

.

PRESSURE BUILDS UP SLOWLY

Check air compressor governor adjustment (paragraph 2-52d).

a

.

If governor doesn’t cut out at 118-120 psi, or doesn’t cut in at 100-102 psi, repair (para 3-25a).

b

.

If governor cut out and cut in pressures are correct, refer to Malfunction 1 above.

If the

malfunction is not corrected in Malfunction 1, repair or replace air compressor (para 2-52e or 3-25b).

3-154