JLG 120-SXJ ANSI Service Manual - Manual (Page 74)

SECTION 5 - HYDRAULICS
5-2 – JLG Lift – 3121105
5. If no repairs are necessary or when repairs have
been made, carefully reconnect hydraulic hoses to
the appropriate ports.
6. If used, remove boom prop or lifting device from
boom, activate hydraulic system and run cylinder
through one complete cycle to check for leaks.
Cylinders w/Dual Counterbalance Valve
Axle Extension Cylinders, Telescope Cylinder, Platform
Slave Level Cylinder
OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION
ONLY.
1. Using all applicable safety precautions, activate
hydraulic system.
2. If working on the telescope cylinder, raise the boom
above horizontal and extend the fly boom approxi-
mately 1 foot (30.5 cm). If working on the platform
slave level cylinder, stroke platform level cylinder for-
ward until platform sits at a 45° angle.
3. Shut down hydraulic system and allow machine to
sit for 10-15 minutes. Turn ignition switch to ON,
move control switch or lever for applicable cylinder
in each direction, then turn ignition switch to OFF.
This is done to relieve pressure in the hydraulic
lines. Carefully remove hydraulic hoses from appro-
priate cylinder port block.
4. There will be initial weeping of hydraulic fluid which
can be caught in a suitable container. After the initial
discharge, there should not be any 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.
5. To check piston seals, carefully remove the counter-
balance valve from the retract port. After initial dis-
charge, there should not be any 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.
6. If no repairs are necessary or when repairs have
been made, replace counterbalance valve and care-
fully reconnect hydraulic hoses to cylinder port
block.
7. Activate hydraulic system and run cylinder through
one complete cycle to check for leaks.
5.3 CYLINDER REMOVAL AND
INSTALLATION
Telescope Cylinder Removal
1. Place machine on a flat and level surface, with axles
extended and the boom fully retracted and in the
horizontal position.
2. Shut down engine. Support boom platform end with
a prop or suitable overhead lifting device.
3. Remove boom end cover.
4. Remove boom length/angle indicator from boom
assembly.
HYDRAULIC LINES AND PORTS SHOULD BE CAPPED IMMEDI-
ATELY AFTER DISCONNECTING LINES TO AVOID THE ENTRY OF
CONTAMINANTS INTO THE SYSTEM.
5. Tag and disconnect hydraulic lines to telescope cyl-
inder. Use suitable containers to retain any residual
hydraulic fluid. Cap hydraulic lines and ports.
HYDRAULIC LINES AND PORTS SHOULD BE CAPPED IMMEDI-
ATELY AFTER DISCONNECTING LINES TO AVOID THE ENTRY OF
CONTAMINANTS INTO THE SYSTEM.
6. Tag and disconnect hydraulic lines to telescope cyl-
inder. Use suitable containers to retain any residual
hydraulic fluid. Cap hydraulic lines and ports.
7. Remove the two (2) cotter pins that retain the tele-
scope rod attach pin to the base boom.
8. Using a suitable brass drift, carefully drive the tele-
scope cylinder rod attach pin from the base boom.
9. Remove the telescope cylinder trunnion attach pin
cover from each side of the base boom.
10. Remove the setscrews securing the telescope cylin-
der attach pin from each side of the telescope cylin-
der trunnion.
11. Using a suitable slide hammer, remove the half pins
attaching the telescope cylinder to the inner mid
boom section.
12. Attach a suitable sling to the telescope cylinder rod.
Support with an overhead crane or other suitable lift-
ing device.
13. Remove the rod support bracket at the aft end of the
base boom.
14. Remove the two (2) extension chain adjusting nuts
at the aft end of the base boom.