JLG 740AJ, Service And Maintenance Manual

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SECTION 4 - BOO M & PLATFOR M
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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 the actuator through housing ports
(do not exceed OEM’s operating pressure). The valve must
be replaced if a steady flow of fluid is seen coming from the
valve ports.
d. Remove the plug and the housing’s valve ports. Operate
the actuator through the housing ports. Conduct the inter-
nal leakage test as described in the Testing section on page
24 of this manual.
e. Re-build the actuator. Remove all rust then polish.
Replacement parts may be needed.
f. Re-build the actuator. Use fluid that is compatible with
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. Check for gear binding. Actuator may not be able to be re-
built and may need to be replaced. Damage could be a result
of overload or shock.
b. Check thread length of port fittings. Fittings should dur-
ing stroke not reach inside the housing bore.
4. Selected position cannot be maintained a. Control or counterbalance valve has internal leak
b. Piston and/or shaft seal leak
c. Air in actuator
a. Disconnect hydraulic lines and bypass valve. Leave valve
ports open and operate the actuator through housing ports
(do not exceed OEM’s operating pressure). The valve must
be replaced if a steady flow of fluid is seen coming from the
valve ports.
b. Remove the plug and the housing’s valve ports. Operate
the actuator through the housing ports. Conduct the inter-
nal leakage test as described in the Testing section on page
24 of this manual.
c. Purge air from actuator. See bleeding procedures.