JLG G12-55A Service Manual - Manual (Page 137)

8-17 G10-55A, G12-55A
Hydraulic System
8.7.7 Steer Select Valve
Machine can be used in front-wheel, four-wheel or crab
steering mode. Steer select valve (8) controls direction of
hydraulic fluid flow to steering cylinder mounted on each
axle. Steer select valve is attached to a mounting plate
under frame near left front corner of cab.
Verify correct operation of steer select valve solenoids
before considering replacement of valve. Refer to Section
9.5, “Electrical System Schematics,” and Section 9.10,
“Display Monitor and Gauges.” Housing of steer select
valve is not serviceable and must be replaced if defective.
a. Steer Select Manifold and Valve Removal
1. Park machine on a firm, level surface, level machine,
fully retract boom, lower 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. Label, disconnect and cap hydraulic hoses and
electrical plugs connected to steering select valve.
6. Remove bolts holding steer select valve to mounting
plate on frame.
7. Remove steer select manifold with attached steer
select valve from machine. Wipe up any hydraulic
fluid spillage in, on, near and around 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 steer select valve from manifold by
removing four socket head capscrews. Discard
four o-rings.
3. Remove solenoid valves and cartridges from steer
select housing.
4. Clean all components with a suitable cleaner
before inspection.
5. Inspect solenoid cartridges for proper operation.
Check by shifting the spool to ensure that it is
functioning properly. Check that 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 manifold DO NOT display an ultra-
smooth, polished finish, or components are
damaged in any way, replace manifold or
appropriate part. Often, dirty hydraulic fluid causes
failure of internal seals and damage to polished
surfaces within 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 steer select valve to mounting plate under left
front side of frame using two bolts.
2. Connect all hydraulic hoses, fittings, solenoid wire
terminal leads, etc., to steer select valve
3. Check 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 batteries.
5. Start engine and run at approximately 1/3-1/2
throttle for about one minute without moving
machine or operating any hydraulic functions.
6. Inspect for leaks and check level of hydraulic fluid in
reservoir. Shut engine OFF.
MY4290
8