JLG G12-55A Service Manual - Manual (Page 132)

Hydraulic System
8-12 G10-55A, G12-55A
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 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 TM 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. Properly connect the batteries.
10. Inspect for leaks and check all fluid levels. The
hydraulic reservoir oil level must be to the middle of
the sight gauge.
c. Pump Test
d. 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 machine on a firm, level surface, level machine,
fully retract boom, raise boom, place transmission
control lever in (N) NEUTRAL, engage park brake and
shut engine OFF.
2. Place a Do Not Operate Tag on both the ignition key
switch and the steering wheel.
3. Open engine cover. Allow system fluids to cool.
4. Properly disconnect the batteries.
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.