Service Manual Instruction Manual

SECTION 4 - BOOM & PLATFORM
3121616 – JLG Lift – 4-21
Troubleshooting
Table 4-1. Troubleshooting
Problem Cause Solution
1. Shaft rotates slowly or not at all a. Insufficient torque output
b. Low rate of fluid flow
c. Control or counterbalance valve has internal leak
d. Piston and/or shaft seal leak
e. Corrosion build-up on the thrust surfaces
f. Swollen seals and composite bearings caused by incom-
patible hydraulic fluid
a. Verify correct operating pressure. Do not exceed OEM’s
pressure specifications. Load may be above maximum
capacity of the actuator.
b. Inspect ports for obstructions and hydraulic lines for
restrictions and leaks.
c. Disconnect hydraulic lines and bypass valve. Leave valve
ports open and operate actuator through housing ports (do
not exceed OEM’s operating pressure). Valve must be
replaced if a steady flow of fluid is seen coming from valve
ports.
d. Remove plug and housing’s valve ports. Operate actuator
through housing ports. Conduct internal leakage test.
e. Rebuild actuator. Remove all rust then polish. Replace-
ment parts may be needed.
f. Rebuild actuator. Use fluid compatible with all seals and
bearings.
2. Operation is erratic or not responsive a. Air in actuator a. Purge air from actuator. See bleeding procedures.
3. Shaft will not fully rotate a. Twisted or chipped gear teeth
b. Port fittings are obstructing the piston
a . C he ck fo r g ea r b ind ing . Ac tu ator ma y n ot be abl e to be
rebuilt and may need to be replaced. Damage could be a
result of overload or shock.
b. Chec k t hre ad le ng th o f po r t f it tin gs. Fi tt in gs sh oul d du r-
ing stroke not reach inside housing bore.
4. S elec t ed po si ti on can no t be m ain ta in ed a . Con tr ol or co un te rb al an ce va lv e h as in te rn al le ak
b. Piston and/or shaft seal leak
c. Air in ac tu ator
a. Disconnect hydraulic lines and bypass valve. Leave valve
ports open and operate actuator through housing ports (do
not exceed OEM’s operating pressure). Valve must be
replaced if a steady flow of fluid is seen coming from valve
ports.
b. Remove plug and housing’s valve ports. Operate actuator
through housing ports. Conduct internal leakage test.
c. Purge air from actuator. See bleeding procedures