JLG sky trak mmv Service Manual page 442

Hydraulic System
5
b. Attachment Tilt Cylinder Disassembly
Note: An additional o-ring may be included at the base
of the cylinder rod. This additional o-ring may be dis-
carded, as it served only in a temporarily protective role.
1. Clean the attachment tilt cylinder (1) with a suitable
cleaner before inspection. Remove all dirt, debris
and grease from the cylinder.
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).
2. If necessary, remove the grease fitting (3) from the
end of the rod (4).
3. Clamp the trunnion end of the attachment tilt
cylinder in a soft-jawed vise or other acceptable
holding equipment if possible.
WARNING:
be trapped inside the cylinder. Exercise caution
when removing a counterbalance valve or a pilot-
operated check valve from a cylinder. Escaping
hydraulic fluid under pressure can penetrate the
skin, causing death or serious injury.
9.144
6
2
9
8
18
21
23
Significant pressure may
17
19
14
15
10
11
22
4. Slowly remove the 4000 psi (276 bar) counterbalance
valve (5) and the pilot-operated check valve (6) from
the attachment tilt cylinder.
5. Extend the rod (4) to allow access to the base of the
cylinder.
IMPORTANT: Protect the finish on the rod at all times.
Damage to the surface of the rod can cause seal failure.
6. Using a pin spanner wrench, unscrew the head
gland (7) from the tube ( 2 ). The head gland was
originally torqued to 300-400 lb/ft (407-542 Nm), so
a considerable amount of force is required to remove
it. Carefully slide the head gland down along the rod
toward the eyelet end, away from the cylinder tube.
IMPORTANT: When sliding the rod and piston assembly
in the tube, prevent the threaded end of the tube from
damaging the piston (8). Keep the rod centered within
the tube to help prevent binding.
7. Carefully pull the rod (4) along with the head
gland (7) and all attachments straight out of the
tube ( 2 ).
8. 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.
1
12
13
7
16
4
3
20
Model MMV Rev. 12/04
20
MT1860