JLG G5-18A Service Manual - Manual (Page 106)

Hydraulic System
8-16 G5-18A, 2505H, 25.5
3. DO NOT open the brake bleeder without holding the
tubing firmly on the bleeder. There is pressure at the
brakes. Have an assistant depress the brake pedal.
Carefully open the bleeder with a 12 mm wrench.
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. If bleeding the service brake circuit, install a vacuum
pump on the brake reservoir and remove the
remainder of the trapped air from the brake system.
5. The inching valve may also require bleeding, refer to
Section 8.11.7, “Inching Valve.”
6. Check brake fluid level and add fluid if necessary.
Refer to Section 2.4, “Fluids, Lubricants and
Capacities.”
d. Brake Performance Test
1. Press down on the service brake pedal. The pedal
should NOT travel to the cab floor. Start the
machine, shift into forward, release the park brake
and slowly accelerate. Apply the service brake
carefully noting the performance of the service brake
system. If the service brakes do not safely stop the
machine, repeat the service brake bleeding
procedure.
8.11.3 Park Brake Valve (G5-18A)
The park brake valve is located in the cab, below the seat.
a. Park Brake Valve Removal
1. Park the machine on a firm, level surface, 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 battery and engine covers. Allow the
system fluids to cool.
4. Properly disconnect the battery.
5. Remove the four capscrews holding the cover below
the seat. The park brake valve is mounted on the
backside of the cover.
6. Label, disconnect and cap the hydraulic hoses on
each side and bottom of the park brake valve.
Disconnect and cap all hoses, fittings, etc.
7. Remove the two capscrews, and two lockwashers
mounting the park brake valve to the cover.
b. Park Brake Valve Disassembly, Cleaning,
Inspection and Assembly
1. Place the park brake valve on a suitable work
surface.
2. Remove the solenoid valve (1) and cartridge (2) from
the park brake housing.
3. Clean all components with a suitable cleaner before
inspection.
4. 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.
5. Inspect internal passageways of the park brake
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 unit.
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.
6. Install the solenoid valves and cartridges in the park
brake housing.
c. Park Brake Valve Installation
1. Install the park brake valve with the two lockwashers
and two capscrews to the cover.
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.
2. Use new oiled o-rings as required. Uncap, reattach
and secure the three hoses.
3. Check the routing of all hoses for sharp bends or
interference with any rotating members, and install
tie wraps and/or protective conduit as required.
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