Lull 944E-42 Service Manual - Manual (Page 331)

8.79 Model 644E-42/944E-42 Rev. 6/04
Hydraulic System
NOTE:
When checking pressures in
circuits, refer to Section 8.7,
“Hydraulic System Testing,” for
correct pressure readings.
Not
OK
Check seals on extend/retract
cylinder.
Repair/replace extend/retract
cylinder.
If OK
If OK
Not
OK
Check counterbalance valve on
extend/retract cylinder.
Replace the counterbalance
valve.
Not
OK
Check pilot operated check valve on
extend/retract cylinder.
Replace the pilot operated
check valve.
If OK
Not
OK
The extend/retract cylinder does
not retract.
Check the standby pump pressure
at implement pump pressure tap.
Replace unloader cartridge
on main control valve.
If OK
Not
OK
Check pilot pressure at “PPG” port
of accumulator charge/secondary
function valve.
Adjust/repair/replace
pressure reducing cartridge
on accumulator charge/
secondary function valve.
If OK
Not
OK
Adjust/replace main relief
cartridge on main control
valve.
If OK
Not
OK
Repair/replace rear joystick.
Check the main relief pump
pressure at implement pump
pressure tap. Refer to Section 8.7,
“Hydraulic System Testing,” test
sequence 7.
Install pressure gauge in the pilot
supply line, between the rear joystick
and the extend/retract section of
main control valve. Check pilot
pressure. With the joystick moved all
the way to the left, the pressure
should be 444 ±22 psi (30,6 ±1,5
bar).
Not
OK
Not
OK
If the extend/retract
cylinder drifts or reacts
slowly, check the seals on
the extend/retract cylinder.
Replace counterbalance and/
or pilot-operated check valves
on the extend/retract cylinder.
Check counterbalance and
pilot-operated check valves.
Repair/replace extend/retract
cylinder.
If OK
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