JLG sky trak mmv Service Manual page 471

11. Remove the piston (12) from the end of the rod (5).
12. Remove the two wear rings (13), the piston seal (14)
and the o-ring (15) from the piston.
c. Fork Side Shift Cylinder Internal Cleaning
1. Remove all hydraulic fluid, dirt and debris from the
inner surface of the cylinder.
2. Discard all seals, back-up rings and o-rings. Replace
with new items from a complete seal kit to help
ensure proper cylinder function.
3. Clean all metal parts with an approved cleaning
solvent such as trichlorethylene. Carefully clean
cavities, grooves, threads, etc.
d. Fork Side Shift Cylinder Inspection and Repair
1. Inspect all parts for wear and damage. If inner
surfaces of the cylinder (1) do not display an ultra-
smooth, polished finish, or are damaged in any way,
replace the damaged part. Often, dirty hydraulic fluid
causes failure of internal seals and damage to the
polished surfaces within the component.
2. Inspect the inside of the tube (2) for scoring and
other damage. If the tube is damaged, replace it with
a new tube.
3. Remove small scratches on the rod or inside of the
tube with very fine grit emery cloth. Use the emery
cloth in a rotary motion to polish out small
imperfections in the metal and blend scratch(es) into
the surrounding surface.
4. Clean the parts with trichlorethylene after repair.
5. Check that the rod (5) is straight. If the rod is bent,
install a new rod.
e. Fork Side Shift Cylinder Assembly
Note: Follow Section 9.14.3, General Cylinder Assem-
bly Instructions.
1. Install a new oiled wear ring (13), new o-ring (15),
new piston seal (14) and another wear ring (13) onto
the piston (12).
2. Place the piston onto the threaded end of the rod (5)
and secure inplace with a new nut (11). Torque the
nut to 275-330 lb/ft (373-447 Nm).
3. Place the rod spacer (10) onto the rod (5) and slide
down against the piston (12).
Model MMV Rev. 12/04
IMPORTANT: Avoid using excess force when clamping
the cylinder in a vise. Apply only enough force to hold the
cylinder securely. Excessive force can damage the cylin-
der tube (2).
4. Fasten the tube (2) in a soft-jawed vise or other
suitable holding device.
5. Lubricate the o-rings on the piston and the inside of
the tube with clean, filtered hydraulic oil. This will aid
in installation.
IMPORTANT: Use a suitable installation tool or com-
pression sleeve to help prevent twisting or damaging the
seals and o-rings when installing the piston (12) into the
cylinder. When sliding the rod and piston assembly in the
tube, DO NOT damage the piston by scraping it against
the threads in the tube. Keep the rod in line with the tube
to prevent binding.
6. Keep the rod (5) straight and carefully insert the rod
into the tube (2). Avoid scratching, nicking or
damaging the tube while installing the rod.
7. Install a new oiled U-cup seal (9) into the rear end of
the guide (4). Use tools that will not damage the
seals.
8. Install a new oiled HD rod wiper seal (6) into the
flange side of the guide (4). The angled edge of the
seal must point toward the flange edge of the guide
away from the cylinder tube (2).
9. Install a new oiled back-up ring (8) and o-ring (7) to
the outside of the guide (4). Carefully install the
guide onto the rod. Use seal protectors or place tape
on the threads of the rod to protect the seals during
installation.
10. Apply a drop of Loctite 242 (blue) removable
threadlocker to the first two threads of the guide (4)
180° apart. Install the guide into the tube (2) and
tighten securely.
11. Apply Loctite 242 (blue) removable threadlocker to
the threads of the setscrew (3) and thread into the
flange of the guide. Tighten the setscrew securely.
12. Test the cylinder at low operating pressure
(100 psi or 6,9 bar) to verify that the piston and rod
move freely in both directions.
13. Increase the operating pressure to the maximum for
the cylinder (4000 psi or 275 bar) and check for
external leakage and for free movement in both
directions.
14. Retract the piston fully.
Hydraulic System
9.173