JLG M4069 Service Manual - Manual (Page 77)

SECTION 4 - HYDRAULICS
3121639 – JLG Lift – 4-5
7. If extend port leakage is less than 6-8 drops per min-
ute, carefully reconnect hose to extend port, then
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
(Lift Cylinder)
OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION
ONLY.
1. Using all applicable safety precautions, activate
hydraulic system.
2. Raise platform completely and place a suitable over-
head lifting device approximately 1 in (2.5 cm) below
the platform.
3. After completing the above, shut down hydraulic
system and allow machine to sit for 10-15 minutes.
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 following cylinder
repairs must be made. If the retract port is leaking,
the piston is leaking, the piston seals are defective
and must be replaced. If the extend port is leaking,
the counterbalance is defective and must be
replaced.
5. If no repairs are necessary or when repairs have
been made, carefully reconnect hydraulic hoses to
the appropriate ports.
6. Remove lifting device from platform, activate hydrau-
lic system and run cylinder through complete cycle
to check for leaks and operation.
Cylinders with Duel Counterbalance Valves
(Oscillating Cylinders)
OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION
ONLY.
1. When working on oscillating axle cylinder, place
machine on firm level surface.
2. Using all applicable safety precautions, activate
hydraulic system.
3. Shut down hydraulic system and allow machine to
sit for 10-15 minutes. This is done to relieve pressure
in the hydraulic lines. Carefully remove hydraulic
hoses from appropriate 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 following cylinder
repairs must be made. If the retract port is leaking,
the piston is leaking, the piston seals are defective
and must be replaced. If the extend port is leaking,
the counterbalance 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, carefully reconnect hydraulic hoses to
the appropriate ports.
7. Activate hydraulic system and run cylinder through
complete cycle to check for leaks and operation.
4.10 CYLINDER REMOVAL AND
INSTALLATION
Lift Cylinder Removal
1. Place the machine on a flat and level surface. Turn
power on and raise the platform. Turn power off and
attach a suitable lifting device to the platform.
2. Remove the bolt, locknut and keeper shaft securing
the cylinder rod attach pin to the upper inner arm
assembly. Using a suitable brass drift, drive out the
rod end attach pin from the arm assembly.
3. Retract the cylinder rod completely.
4. Tag and disconnect, then cap the lift cylinder
hydraulic lines and ports.
5. Remove the bolt, locknut and keeper shaft securing
the cylinder barrel attach pin to the upper inner arm
assembly. Using a suitable brass drift, drive out the
rod end attach pin from the arm assembly.
6. Carefully remove the cylinder from the scissor lift
and place in a suitable work area.