JLG sky trak mmv Service Manual page 313

Before troubleshooting any
hydraulic circuit, ALWAYS
begin by checking the
following:
1. Hydraulic oil level in the
reservoir
2. All hoses, tubes, fittings
for leaks, kinks,
interference, etc.
3. Air in the lines
NOTE:
When checking pressures in
circuits, refer to Section 9.7,
Hydraulic System Testing for
correct pressure readings.
Model MMV Rev. 12/04
If park brake fails to hold,
check the "PBG" port on
the secondary function
manifold. Should read 0 psi.
If park brake fails to
release, check the "PBG"
port on the secondary
function manifold. Should
read 550 ±100 psi
(37,9 ±7 bar).
Check relief valve on
secondary function
manifold.
If OK
Check solenoid valves on the
secondary function manifold.
Check solenoid valve
cartridges.
If OK
Check front brake
discs for wear.
If OK
Within the front axle:
If not holding, check the park
brake springs.
If not releasing, check the
piston seals.
Hydraulic System
Adjust/repair/replace
Not
OK
relief valve.
Refer to Section 10.13.5,
Not
OK
Parking Brake Switch .
If OK
Install seal kit/replace
Not
OK
solenoid valve cartridges.
Refer to Section 2.13.12,
Not
OK
Brake Disc Wear Check .
Refer to ZF Axle Repair
Not
Manual, Model MS-T 3060,
OK
ZF part number 5871 560 002.
JLG part # 8990430
9.15