JLG 450AJ Service Manual - Manual (Page 24)

SECTION 2 - PROCEDURES
2-8 – JLG Lift – 3120869
8. Position LIFT control switch to DOWN and hold until
boom reaches horizontal; check boom length
against measurement. If boom has retracted more
than 2.5 cm (1 inch) and oil is leaking around rod-
end of telescope cylinder (check with light and
inspection mirror), seals are defective and require
replacement, or cylinder rod is scored and cylinder
requires overhaul or replacement. If boom has
retracted and oil is leaking from counterbalance
valve, the valve is either improperly adjusted, or
defective and requires replacement.
9. Connect hydraulic lines to control valve.
Lift Cylinder
NOTE: Switches referenced in this procedure are located on
the Ground Control Panel.
1. Activate hydraulic system, properly set extendable
axles and position boom in stowed position; adhere
to all safety precautions.
NOTE: Tape measure or cord should be at least 2 meters (6
feet) long for use in this test.
2. Attach tape measure or cord to bottom of platform.
BEFORE RAISING BOOM, ENSURE THAT AREAS ABOVE AND
BELOW BOOM AND PLATFORM ARE CLEAR OF ALL OBSTRUC-
TIONS AND PERSONNEL.
3. With boom fully retracted, place LIFT control switch
to UP and hold until platform is approximately 2
meters (6 feet) above ground level. Shut down
engine.
4. Tag and carefully disconnect hydraulic lines to lift
cylinder at control valve. Use a suitable container to
retain any residual hydraulic fluid.
5. Observe oil flow from cylinder lines. Oil leaking from
extend port hose indicates a leaking counterbalance
valve. Oil leaking from retract port hose indicates
leakage by cylinder piston.
6. Leave boom elevated in test position for approxi-
mately one (1) hour.
7. With tape measure or cord used for reference,
check to see whether boom has lowered (crept)
more than 7.5 cm (3 inches).
8. If boom has lowered and oil is leaking around rod-
end cap of cylinder, seals in cylinder are defective
and require replacement. If boom has lowered and
oil is leaking from the counterbalance valve, the
valve is either improperly adjusted or defective and
requires replacement.
E N S U R E T H AT H Y D R A U L I C L I N E S A R E C O N N E C T E D A S
MARKED PRIOR TO BEING DISCONNECTED.
9. Connect hydraulic lines to control valve.
2.8 CYLINDER CHECKING PROCEDURE
IF PERFORMING MAINTENANCE ON THE BOOM CYLINDERS, DO
NOT USE A LIFTING DEVICE TO LIFT THE BOOMS UNLESS THE
HOLDING VALVES HAVE BEEN REMOVED FIRST. FAILURE TO DO
SO WILL RESULT IN SEVERE DAMAGE TO THE BOOM.
NOTE: Cylinder check must be performed anytime a system
component is replaced or when improper system
operation is suspected.
Cylinders Without Counterbalance Valves -
Master Cylinder and Steer Cylinder
1. Using all applicable safety precautions, activate
engine and fully extend cylinder to be checked. Shut
down engine.
2. Carefully disconnect hydraulic hoses from retract
port of cylinder. There will be some initial weeping of
hydraulic fluid which can be caught in a suitable
container. After the initial discharge, there should be
no further drainage from the retract port.
3. Activate engine and extend cylinder.
4. If cylinder retract port leakage is less than 6-8 drops
per minute, carefully reconnect hose to port and
retract cylinder. If leakage continues at a rate of 6-8
drops per minute or more, cylinder repair must be
made.
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
minute, 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.