JLG sky trak mmv Service Manual page 447

8. Remove the precision wearband (10) and the
capped T-seal (11) from the piston (5).
Note: The T-seal actually consists of four components; a
wide, flexible inner band, the flexible T-seal band itself,
and two supportive split caps that mount on either side of
the "T" itself.
9. Remove the locknut (13) from the rod (3). The
deforming-thread type nut was coated with Loctite
#271 (red) and torqued to 750-800 lb/ft (1017-1085
Nm). Discard the nut.
Note: It may be necessary to apply heat to break the
bond of the sealant between the locknut (13) and the rod
(3) before the piston (5) can be removed. Some parts of
cylinders are sealed with a special organic sealant and
locking compound.
Before attempting to disassemble these parts, remove
any accessible seals from the area of the bonded joint.
Wipe off any hydraulic oil and heat the joint uniformly to
break the bond. A temperature of 300-400° F (149-204° C)
will destroy the bond. Avoid overheating or the parts may
become distorted or damaged. Apply sufficient torque or
pressure for removal while the parts are still hot.
Breakdown of sealant will leave a white, powdery resi-
due on threads and parts. Clean the residue away with a
soft brass wire brush prior to reassembly, and wipe with
Loctite "T" cleaner before reinstallation.
10. Remove the piston (5) and head gland (4) from the
rod (3).
11. From within the head gland (4), remove the deep
Z-seal with rod back-up (14) and the sealed outside
diameter heavy-duty rod wiper (15).
12. From within the piston (5), remove the precision
wearband (16) and the small o-ring (17).
c. Slave Cylinder 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 (12) 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.
Model MMV Rev. 12/04
Note: If a white, powdery residue is present on threads
and parts, it can be removed. Clean the residue away
with a soft brass wire brush prior to reassembly, and
wipe with Loctite "T" cleaner before reinstallation.
d. Slave Cylinder Inspection
1. Inspect internal surfaces and all parts for wear, damage,
etc. If the inner surface of the tube (2) does not display a
smooth finish, or is scored or damaged in any way,
replace the tube. Often, dirty hydraulic fluid causes
failure of internal seals and damage to the smooth
surface within the tube.
2. Remove slight scratches on the piston, rod, or inner
surface of the tube with very fine grit emery cloth. Use
the emery cloth in a rotary motion to polish out and
blend the scratch(es) into the surrounding surface.
3. Clean parts with trichlorethylene.
4. Check that the rod (3) is straight. If it is bent, install a
new rod.
e. Slave Cylinder Assembly
Note: Follow Section 9.14.3, General Cylinder Assem-
bly Instructions.
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 and head
gland 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.
1. Fasten the rod end in a soft-jawed vise and put a
padded support below and near the threaded end of
the rod to help prevent damage to the rod.
2. Install the small o-ring (17) and the precision
wearband (16) in the piston (5).
3. Install the sealed outside diameter heavy-duty rod
wiper (15). The wiper lip (18) should be toward the
outer end of the head gland and the seal lips toward
the inner end of the head gland. Use tools that will
not damage the seals.
4. Install the deep Z-seal with rod back-up (14) in the
head gland (4) orienting the edge (19).
5. Carefully install the head gland (4) onto the rod (3).
6. Carefully install the piston (5) onto the rod (3).
Hydraulic System
9.149