JLG G12-55A Service Manual - Manual (Page 136)

Hydraulic System
8-20 G10-55A, G12-55A
8.7.8 Steer Select Valve
The machine can be used in the front-wheel, four-wheel
or crab steering mode. The steer select valve (8) controls
the direction of hydraulic fluid flow to the steering cylinder
mounted on each axle. The steer select valve is attached
to a mounting plate under the frame near the left front
corner of the cab.
Verify the correct operation of the steer select valve
solenoids before considering replacement of the valve.
Refer to Section 9.5, “Electrical System Schematics,” and
Section 9.11, “Display Monitor and Gauges.” The housing
of the steer select valve is not serviceable and must be
replaced if defective.
a. Steer Select Manifold and Valve Removal
1. Park the machine on a firm, level surface, level the
machine, fully retract the boom, lower 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. Label, disconnect and cap the hydraulic hoses and
the electrical plugs connected to the steering select
valve.
6. Remove the bolts holding the steer select valve to
the mounting plate on the frame.
7. Remove the steer select manifold with the attached
steer select valve from the machine. Wipe up any
hydraulic fluid spillage in, on, near and around the
machine.
b. Steer Select Manifold and Valve Disassembly,
Cleaning, Inspection and Assembly
1. Place the steer select assembly on a suitable work
surface.
2. Separate the steer select valve from the manifold by
removing the four socket head capscrews. Discard
the four o-rings.
3. Remove the solenoid valves and cartridges from the
steer select housing.
4. Clean all components with a suitable cleaner before
inspection.
5. Inspect the solenoid cartridges for proper operation.
Check by shifting the spool to ensure that it is
functioning properly. Check that the spring is intact.
Inspect the cartridge interior for contamination.
6. Inspect internal passageways of the steer select
manifold and valve for wear, damage, etc. If inner
surfaces of the manifold DO NOT display an ultra-
smooth, polished finish, or components are
damaged in any way, replace the manifold or
appropriate part. Often, dirty hydraulic fluid causes
failure of internal seals and damage to the polished
surfaces within the secondary function manifold.
Note: ALWAYS replace seals, o-rings, gaskets, etc.,
with new parts to help ensure proper sealing and
operation. Lubricate seals and o-rings with clean
hydraulic oil.
7. Install the solenoid valves and cartridges in the steer
select housing.
8. Attach the steer select valve to the manifold using
four new, oiled o-rings and the four socket head
capscrews.
c. Steer Select Valve and Manifold Installation
1. Install the steer select valve to the mounting plate
under the left front side of the frame using the two
bolts.
2. Connect all the hydraulic hoses, fittings, solenoid
wire terminal leads, etc., to the steer select valve
3. Check the routing of all hoses, wiring and tubing for
sharp bends or interference with any rotating
members, and install tie wraps and/or protective
conduit as required. Tighten all hose clamps.
4. Properly connect the battery.
5. Start the engine and run at approximately 1/3-1/2
throttle for about one minute without moving the
machine or operating any hydraulic functions.
MY4290
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