JLG G12-55A Service Manual - Manual (Page 131)

8-15 G10-55A, G12-55A
Hydraulic System
Note: DO NOT disassemble the operating pump. The
pump is pre-set from the manufacturer. Any adjustments
or repairs performed by anyone other than an authorized
dealer could void the warranty.
b. Pump Installation
1. Place the pump and a new, oiled o-ring into position
on the transmission. Align the pump shaft with the
internal transmission gear, so that the machined
teeth mesh together.
2. Align the bolt holes with the pump mount holes.
3. Apply Loctite ® 242 to the previously removed bolts.
4. Secure the pump to the transmission with the four
bolts and washers. Torque as required.
5. Uncap and connect the previously labeled hydraulic
hoses to their appropriate locations.
6. Fill the hydraulic reservoir. Refer to Section 8.5.2,
“Hydraulic Oil Reservoir Filling.”
7. Prime the pump by filling the case drain port with fresh,
filtered hydraulic oil from a clean container before
installing the case drain connector and hose.
8. Check all routing of hoses and tubing for sharp
bends or interference with any rotating members. All
tube and hose clamps must be tight.
9. Remove the 10 amp fuse from location F3 in power
distribution unit located in the engine compartment.
This will allow the engine to crank, but not start while
air is worked out of the new pump.
10. Connect a hose to the “P1” port on the pump. Direct
the open end of the hose into a fluid drip pan.
11. Properly connect the battery.
12. Turn the machine ignition switch to START and back
OFF in 3 to 5 second intervals. Monitor the open end
of the drain hose for a constant flow of fluid (no air)
while engine is cranking.
13. Once a constant flow is achieved at the open end of
the drain hose, disconnect the hose and reinstall the
10 amp fuse to location F3 in the power distribution
unit.
14. Inspect for leaks and check all fluid levels. The
hydraulic reservoir oil level must be to the middle of
the sight gauge.
15. Remove the Do Not Operate Tags from both the
ignition key switch and the steering wheel.
c. Pump Test
Refer to Section 8.3.1, “Pressure Checks and
Adjustments.”
8.7 CONTROL VALVES
8.7.1 Main Control Valve
The main control valve is mounted at the top of the
chassis in front of the mast supports.
The main control valve assembly consists of individual
working sections with their own valve assemblies, each
providing a specific hydraulic function.
a. Main Control Valve Removal
1. Park the machine on a firm, level surface, level the
machine, fully retract the boom, raise the boom, place
the transmission control lever in (N) NEUTRAL,
engage the park brake and shut the engine OFF.
2. Place a Do Not Operate Tag on both the ignition key
switch and the steering wheel, stating that the
machine should not be operated.
3. Open the engine cover. Allow the system fluids to
cool.
4. Properly disconnect the battery.
5. Close the engine cover.
6. Remove the main valve cover.
7. Thoroughly clean the main control valve and
surrounding area, including all hoses and fittings,
before proceeding.
8. Drain the hydraulic fluid reservoir. Refer to Section
8.5.1, “Hydraulic Oil Reservoir Draining.”
9. Place a suitable container to catch hydraulic fluid
drainage beneath the frame.
Note: Slowly remove the hydraulic hoses attached to
the main control valve to relieve any possible trapped
pressure in the hydraulic line.
10. Label, disconnect and cap all the hydraulic hoses,
tubes and wires at the main control valve.
11. Wipe up any hydraulic fluid spillage in, on, near and
around the machine and the work area.