Service Manual

8.19
Model 8042, 10042, 10054 Legacy Rev. 10/03
Hydraulic System
Not
OK
Not
OK
Not
OK
Not
OK
Not
OK
Not
OK
Check pressure at front axle.
If service brakes are not
holding, check the pressure
at the brake valve.
Replace brake valve.
Check the brakes for
mechanical failure.
If OK
Replace brake valve.
If park brake fails to hold,
check the “PBG” port on
the secondary function
manifold. Should read
0psi.
If park brake fails to
release, check the “PBG”
port on the secondary
function manifold. Should
read 550 psi (38 bar).
Check pressure reducing
valve on secondary
function manifold.
Refer to Section 9.14,
“Switches and Solenoids.”
Not
OK
Within the front axle:
If not holding, check the park
brake springs.
If not releasing, check the
piston seals.
Refer to Section 5.3.8, “ZF
Axle Repair Manuals,” for
proper ZF Axle Repair
Manual for further
information.
Install seal kit/replace
solenoid valve cartridges.
If OK
Adjust/repair/replace
pressure reducing valve.
If OK
Check solenoid valve
cartridges.
Check solenoid valves on the
secondary function manifold.
Refer to Section 5.3.8, “ZF
Axle Repair Manuals,” for
proper ZF Axle Repair
Manual for further
information.
If OK
If OK
NOTE:
When checking pressures in
circuits, refer to Section 8.7,
“Hydraulic System Testing,” for
correct pressure readings.
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
Not
OK
Check front and rear brake
discs for wear.
Refer to the appropriate
Legacy Owners/Operators
Manual.
If OK