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SECTION 3 – TROUBLESHOOTING
3120933 Rev. 0
USTC
3-7
Hoist drive motor defective.
Check valve in hoist sticking in
closed position.
Return relief valve in hoist stuck
in closed position.
Hoist primary drive assembly
damaged.
Relief valve in hoist control
valve inlet section set too low.
Hoist brake clutch defective.
Uneven hoist mounting.
Excessive back pressure at hoist
motor manifold.
Hoist brake defective.
Hoist control valve spool stuck in
open position.
Relief valve in hoist control
valve opening and closing.
Hoist friction brake intermittently
engaging and releasing.
Anti-two-block valve not opening
completely.
Load capacity exceeded.
Hydraulic oil level low.
Restricted or broken hydraulic
line.
Malfunctioning hydraulic pump.
Control cable broken, kinked or
disconnected.
Check valve in lift control valve
inlet stuck in closed position.
Worn control valve spool.
Main relief valve spool too low.
Holding valve in lift cylinder
stuck in closed position.
Excessive oil leak past lift
cylinder piston seal.
TROUBLE
PROBABLE CAUSE
REMEDY
Table 3-4. Hydraulic Components (continued)
Hoist will not raise load or load
handling device.
Hoist will not raise load or load
handling device (continued).
Hoist lowers load with control
lever in neutral.
Hoist chatters while raising or
lowering load.
Boom will not elevate.
Repair or replace hoist motor.
Repair or replace sticking valve.
Disassemble hoist and repair or
replace relief valve.
Disassemble hoist and repair
replace primary drive.
Adjust or replace relief valve.
Disassemble hoist and repair or
replace clutch.
Check hoist for correct
mounting.
Check hoist counterbalance
valves and repair.
Disassemble hoist and repair or
replace brake.
Clean or replace valve section.
Clean or replace relief valve.
Disassemble hoist and repair or
replace brake system.
Repair or replace anti-two-block
solenoid valve.
Reduce load. Refer to Load
Capacity Chart.
Add oil.
Remove line and clear
obstruction or replace line.
Repair or replace pump.
Repair or replace control cable.
Clean or replace sticking valve.
Check pressure delivery to valve
and clean or replace section.
Adjust or replace relief valve.
Clean or replace defective valve.
Repair or replace cylinder.