JLG 120HX Service Manual - Manual (Page 35)

SECTION 2 - PROCEDURES
3120819 – JLG Lift – 2-13
Master Level Cylinder Removal
1. With the main boom positioned to horizontal and
properly supported, prepare to remove the upright
level cylinder.
2. Remove the bolt, lockwasher and nut securing the
level cylinder rod attach pin to the tower boom.
Using an appropriate brass drift, drive out the level
cylinder rod attach pin.
3. Tag, disconnect and cap hydraulic lines to level cyl-
inder.
NOTE: When disconnecting hydraulic lines, any residual
hydraulic fluid should be drained into a suitable con-
tainer.
4. Make up two temporary hose assemblies (3/8 In. x
10 ft.) to carry power from the turntable swing motor
supply hoses to the lift cylinder. Couple temporary
hoses to swing motor supply hoses, using reducer
fittings if necessary. Plug ports in swing motor.
5. After installing temporary hoses, activate swing func-
tion, using auxiliary power, to fully retract level cylin-
der rod.
6. Remove temporary hoses from level cylinder and
cap them. Plug cylinder ports.
7. Using slings, restrain level cylinder.
8. Remove retaining plate and bolts from upright cylin-
der attach pin.
9. Using an appropriate brass drift, drive out the
upright attach pin. Carefully remove restraining
slings and remove level cylinder from boom.
Master Level Cylinder Installation
1. With the boom positioned at horizontal and properly
supported, place the master level cylinder in posi-
tion on the boom and secure in place using slings.
2. Align barrel end bushing with pin attach blocks in
turntable upright and install upright attach pin using
appropriate brass drift. Secure pin with retaining
plate and retaining plate bolts.
3. Remove caps from temporary hydraulic lines and
attach to level cylinder ports. Using auxiliary power,
activate swing function and extend cylinder rod until
rod bushing aligns with boom lift cylinder rod end
attach bushing.
4. Using an appropriate brass drift drive the rod attach
pin through the aligned bushings of the cylinder rod
and boom lift cylinder rod end attach plate, taking
care to align holes for bolt attachment. Secure rod
end attach pin with bolt, lockwasher and nut.
5. Remove restraining slings from level cylinder.
6. Remove temporary hydraulic lines from cylinder
ports and turntable swing motor hydraulic supply.
Reattach hydraulic supply to swing motor.
7. Remove caps from cylinder hydraulic lines and cor-
rectly install lines to cylinder.
8. Remove boom support. Place boom in stowed posi-
tion. Check hydraulic fluid level and adjust accord-
ingly.
2.11 CYLINDER REPAIR
NOTE: The following are general procedures that apply to
all of the cylinders on this machine. Procedures that
apply to a specific cylinder will be so noted.
Disassembly
DISASSEMBLY OF THE CYLINDER SHOULD BE PERFORMED ON
A CLEAN WORK SURFACE IN A DIRT FREE WORK AREA.
1. Connect a suitable auxiliary hydraulic power source
to the cylinder port block fitting.
DO NOT FU LLY EXTEN D CYLINDER TO END OF STROKE.
RETRACT CYLINDER SLIGHTLY TO AVOID TRAPPING PRES-
SURE.
2. Operate the hydraulic power source and extend the
cylinder. Shut down and disconnect the power
source. Adequately support the cylinder rod, if appli-
cable.
FOR CYLINDERS WITH DOUBLE HOLDING VALVES, CRACK
BLEEDERS TO RELEASE PRESSURE BEFORE REMOVING HOLD-
ING VALVES.