JLG 740AJ Service Manual - Manual (Page 290)

SECTION 5 - HYDRAULICS
5-4 – JLG Lift – 3121160
5. With cylinder fully retracted, shut down engine and
carefully disconnect hydraulic hose from cylinder
extend port.
6. Activate engine and retract cylinder. Check extend
port for leakage.
7. If extend port leakage is less than 6-8 drops per min-
ute, carefully reconnect hose to extend port, than
activate cylinder through one complete cycle and
check for leaks. If leakage continues at a rate of 6-8
drops per minute or more, cylinder repairs must be
made.
Cylinders With Single Counterbalance
Valve
Main Lift (upper) Cylinder.
OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION
ONLY.
1. Using all applicable safety precautions, activate
hydraulic system.
WHEN WORKING ON THE MAIN LIFT CYLINDER, RAISE THE
BOOM TO HORIZONTAL AND SUPPORT THE MAIN BOOM,
UPRIGHT, AND TOWER BOOM. DO NOT WORK ON THE CYLIN-
DER WITHOUT A SUITABLE SUPPORT IN PLACE.
2. Shut down hydraulic system and allow machine to
sit for 10-15 minutes. If machine is equipped with
bang-bang or proportional control valves, turn IGNI-
TION SWITCH to ON, move control switch or lever
for applicable cylinder in each direction, then turn
IGNITION SWITCH to OFF. If machine is equipped
with hydraulic control valves, move control lever for
applicable cylinder in each direction. This is done to
relieve pressure in the hydraulic lines. Carefully
remove hydraulic hoses from appropriate cylinder
port block.
3. There will be initial weeping of hydraulic fluid, which
can be caught in a suitable container. After the initial
discharge, there should be no further leakage from
the ports. If leakage continues at a rate of 6-8 drops
per minute or more, the counterbalance valve is
defective and must be replaced.
4. To check piston seals, carefully remove the counter-
balance valve from the retract port. After initial dis-
charge, there should be no further leakage from the
ports. If leakage occurs at a rate of 6-8 drops per
minute or more, the piston seals are defective and
must be replaced.
5. If no repairs are necessary or when repairs have
been made, replace counterbalance valve and care-
fully connect hydraulic hoses to cylinder port block.
6. If used, remove lifting device from upright or remove
prop from below main boom, activate hydraulic sys-
tem and run cylinder through one complete cycle to
check for leaks.
Cylinders With Dual Counterbalance
Valves
(Articulating Jib Boom Lift, and Slave), Slave Level, Tower
Lift, Upright level, Main Telescope
OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION
ONLY.
1. Using all applicable safety precautions, activate
hydraulic system.
IF WORKING ON THE TOWER BOOM LIFT CYLINDER, RAISE
TOWER BOOM HALFWAY, FULLY ELEVATE MAIN BOOM WITH
TELESCOPE CYLINDER FULLY RETRACTED AND ATTACH AN
OVERHEAD CRANE TO THE UPRIGHT FOR SUPPORT, LEAVING
APPROXIMATELY 1 INCH (2.54 CM) OF SLACK IN CHAIN OR
SLING FOR TEST PURPOSES. IF WORKING ON THE UPRIGHT
LEVEL, RAISE THE TOWER BOOM HALFWAY, THEN RAISE MAIN
BOOM TO HORIZONTAL, AND SUPPORT WITH A CRANE OR
SUITABLE LIFTING DEVICE, APPROXIMATELY 1 INCH (2.54 CM)
BELOW MAIN BOOM. IF WORKING ON THE PLATFORM LEVEL
CYLINDER, STROKE PLATFORM LEVEL CYLINDER FORWARD
UNTIL PLATFORM SITS AT A 45 DEGREES ANGLE.
2. Shut down hydraulic system and allow machine to
sit for 10-15 minutes. If machine is equipped with
bang-bang or proportional control valves, turn IGNI-
TION SWITCH to ON, move control switch or lever
for applicable cylinder in each direction, then turn
IGNITION SWITCH to OFF. If machine is equipped
with hydraulic control valves, move control lever for
applicable cylinder in each direction. This is done to
relieve pressure in the hydraulic lines. Carefully
remove hydraulic hoses from appropriate cylinder
port block.