JLG G12-55A AccuPlace Service Manual - Manual (Page 110)

Hydraulic System
8.20 G10-55A & G12-55A AccuPlace
the brakes to apply properly. There are four brake
bleeder locations on the axles. Work with an assistant to
perform this procedure.
1. Place the travel select lever in (N) NEUTRAL,
engage the park brake, and start the engine.
2. Remove the plastic cap from the brake bleeder (14).
Attach one end of a length of transparent tubing over
the brake bleeder. Place the other end of this tubing
in a suitable transparent container that is partially
filled with hydraulic oil. The end of the tubing must be
below the oil level in the container.
3. DO NOT open the brake bleeder without holding the
tubing firmly on the bleeder. There is pressure at the
brakes. Carefully open the bleeder with a 12 mm
wrench. Have the assistant depress the brake pedal.
Close the brake bleeder when air bubbles no longer
appear in the oil. Release the brake pedal. Remove
the tubing from the brake bleeder.
4. Repeat Steps 2 and 3 for the remaining brake
bleeders.
5. Install a vacuum pump on the brake reservoir and
remove the remainder of the trapped air from the
brake system.
6. Check brake fluid level and add fluid if necessary.
7. Conduct a pressure and function check of the
service brake. Refer to Section 8.4.1, “Hydraulic
Pressures.”
8.8.9 Steering Orbitrol Valve
The steering orbitrol valve (15) is located at the base of
the steering wheel shaft, concealed by the lower dash
cover. The valve is not serviceable and must be replaced
in its entirety if defective. For detailed information refer to
Section 4.3.1, “Steering Column and Orbitrol Valve.”
8.8.10 Steer Select Valve
The machine can be used in the front-wheel, four-wheel
or crab steering mode. The steer select valve (16)
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 on the underside of the
frame near the transmission.
Verify the correct operation of the steer select valve
solenoids before considering replacement of the valve.
Refer to Section 9.6, “Electrical System Schematics And
Diagrams,” and Section 9.12, “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.
MY0150
14
MZ0370
15
MAP0280
16