FIFTH WHEEL HYDRAULIC SYSTEM TROUBLESHOOTING

TM 9-2320-285-24-2

3-40. FIFTH WHEEL HYDRAULIC SYSTEM TROUBLESHOOTING

MALFUNCTION

TEST OR INSPECTION

CORRECTIVE ACTION

1. FIFTH WHEEL DOESN'T LIFT

WARNING

Keep clear of fifth wheel boom moving parts to prevent serious injury or death.

Step 1. Check for full movement of fifth wheel hydraulic control valve metering spool.

Have assistant operate 5th WHEEL control lever; watch movement of hydraulic control valve metering

spool.

a. If metering spool does not move fully to "raise" or "lower" positions, repair or replace hydraulic control

valve or cable (para 3-42c and 2-78a).

b. If control valve metering spool moves fully to "raise" and "lower" positions, proceed to step 2 below.

Step 2. Check hydraulic control valve relief pressure.

Disconnect hoses from two top ports of fifth wheel hydraulic control valve and install a pressure gage in

each port.

CAUTION

Do not hold 5th WHEEL control lever back for more than 30 seconds at a time. Failure to follow this

procedure could result in damage to the fifth wheel hydraulic pump.

With vehicle engine at governed speed, have assistant pull back 5th WHEEL control lever fully; watch

both pressure gages.

a. If pressure gage in top rear port indicates 2000 psi and pressure gage in top front port indicates

approximately zero psi, proceed to Malfunction 3, step 2, below.

b. If pressure gage in top rear port indicates less than 2000 psi, but more than 1500 psi, adjust hydraulic

control valve relief pressure (para 3-42c). If pressure increases to 2000 psi without turning adjusting

screw in all the way, return tractor to normal operation. If pressure does not increase when adjusting

screw is turned, proceed to Malfunction 2, step 2, below.

c. If pressure gage in top rear port indicates less than 1500 psi, proceed to Malfunction 2, step 2, below.

3-408