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 417 of 698
TM 9-2320-285-24-2
3-40.
FIFTH WHEEL HYDRAULIC SYSTEM TROUBLESHOOTING (CONT)
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
3.
FIFTH WHEEL CREEPS DOWNWARD
Step 1
.
Check if hydraulic control valve metering spool is in neutral position.
a
.
If metering spool is not in neutral position, repair hydraulic control valve or cable as required (para 3-42
c and 2-78a).
b
.
If metering spool is in neutral position, proceed to step 2 below.
Step 2
.
Lower fifth wheel boom fully.
Disconnect hose from bleed valve (para 2-87b(2)) and cap the hose and bleed valve.
Raise fifth wheel boom fully and check for downward creep.
a
.
If fifth wheel boom does not creep downward, bleed valve is defective; replace (para 2-78b(2)).
b
.
If fifth wheel boom creeps downward, lower fifth wheel boom fully, reconnect hose to bleed valve, and
proceed to step 3 below.
Step 3
.
Raise fifth wheel boom fully; support boom in raised position.
Disconnect two fifth wheel hydraulic cylinder hoses from the down-stroke ends of hydraulic cylinders (para
2-78b(2)) and cap the hoses.
Install a pressure gage in each hydraulic cylinder port.
Have an assistant pull back 5th WHEEL control lever fully; watch pressure gages.
a
.
If pressure gages indicate approximately zero psi and do not increase, hydraulic control valve is
leaking internally; repair or replace (para 3-42c).
b
.
If pressure gage indicates increased pressure, hydraulic cylinder is leaking internally; repair or replace
(para 3-42d).
4.
FIFTH WHEEL DOESN’T LOWER
Step 1
.
Check hydraulic cylinder rods for bent or jammed condition.
a
.
If hydraulic cylinder rods are bent or jammed, repair or replace cylinders (para 3-42d).
b
.
If hydraulic cylinder rods are not bent or jammed, proceed to step 2 below.
3-411
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