JLG G12-55A Service Manual - Manual (Page 135)

8-15 G10-55A, G12-55A
Hydraulic System
b. Service Brake Valve Installation
1. Install the service brake valve (4) with the four
capscrews, four lockwashers and four nuts (3) onto
the service brake bracket (5).
2. Install the service brake pedal. Refer to Section
4.3.2, “Service Brake Pedal.”
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.
3. Use new oiled o-rings as required. Uncap and
connect the previously labeled hoses to the service
brake valve.
4. Check the routing of all hoses, and tubing for sharp
bends or interference with any rotating members,
and install tie wraps and/or protective conduit as
required. Tighten all tube and hose clamps.
5. Properly connect the batteries.
6. Start engine and run at approximately one-third to
one-half throttle for about one minute, without moving
machine or operating any hydraulic functions.
7. Inspect the service brake valve and connections for
leaks, and check the level of the hydraulic fluid in the
reservoir. Shut the engine OFF.
Note: Check for leaks, and repair as required before
continuing. Add hydraulic fluid to reservoir as needed.
8. Wipe up any hydraulic fluid spillage in, on, near and
around the machine, work area and tools.
9. Close and secure the engine cover.
10. Remove the Do Not Operate Tags from both the
ignition key switch and the steering wheel.
8.7.4 Service Brake Bleeding
Carefully bleed the brake lines as soon as the brake valve
is installed in the machine. Air in the system will not allow
the brakes to apply properly. There are four brake
bleeder located on the front axle (two inner service brake
bleeders and two outer park brake bleeders) and two
service brake bleeders on the rear axle). Work with an
assistant to perform this procedure.
1. Place transmission control lever in (N) NEUTRAL,
engage the park brake, and start engine.
2. Remove plastic cap from one service brake bleeder
(6). Attach one end of a length of transparent tubing
over brake bleeder. Place other end of this tubing in
a suitable transparent container that is partially filled
with hydraulic oil. The end of tubing must be below
oil level in container.
3. Have assistant depress brake pedal. DO NOT open
service brake bleeder without holding tubing firmly
on bleeder. There is pressure at brakes. Carefully
open bleeder with a 12 mm. wrench. Close service
brake bleeder when air bubbles no longer appear in
oil. Release brake pedal. Remove tubing from
service brake bleeder.
4. Repeat Steps 2 and 3 for the remaining service
brake bleeders.
5. Check hydraulic oil level and add if necessary.
6. Conduct a pressure and function check of service
brake. Refer to Section 8.4.1, “Hydraulic Pressures.”
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