JLG 680S Service Manual - Manual (Page 248)

SECTION 5 - HYDRAULICS
5-8 – JLG Lift – 3121234
Steer Cylinder Seal Repair Instructions
1. The cylinder should be disassembled in a clean
environment to prevent dirt or other contamination
from entering the interior of the cylinder. Clean any
accumulated dirt or debris from the port openings
and guide area. Remove the port plugs and drain oil
from the cylinder. Do not reinstall the port plugs at
this time. No special tools are required for disassem-
bly, but snap ring pliers would ease removal of the
snap ring that retains the rod guide. Items that
should be at hand are a vise, Flat punch, hammer,
rubber hammer, clean oil, and a wrench for removal
of the piston nut. A piston ring compressor is sug-
gested for resizing new teflon piston seals used in
some cylinders.
2. Secure in vise at approximately the mid-point of the
cylinder wall. Do not tighten vise excessively, the
wall may be distorted.
3. If the steer cylinder has a retaining plate on front of
the rod guide, remove the cap screws and dismount
the retaining plate. Remove the retaining ring with
snap ring pliers. If the steer cylinder has an external
spiral retaining ring ahead of the rod guide internal
retaining ring, carefully remove both rings.
4. Pull the rod vigorously outward and allow the piston
to bump the rod guide. The momentum of the rod
should be sufficient to pull the rod guide an piston
from the cylinder barrel. Be careful not to mar the
chromed surface rod.
NOTE: The piston seal and rod guide static seal will likely be
cut on removal from the barrel. This is normal and
cannot be avoided on disassembly.
5. Being careful not to mar the chromed surface,
secure the rod so that the piston nut can be
removed. Remove the piston nut, piston, spacer
tube (if any) and rod guide.
NOTE: The position and orientation of the seals before
replacing them
6. Be careful not to scratch the seal grooves when
removing the old seals. The seals can be removed
with a sharp tool like an awl by carefully pushing the
point partially into the seal and prying the seal from
the groove. Carefully cutting the seal apart with an X-
acto knife will also ease removal.
7. Inspect the seal grooves and clean away any con-
tamination. Apply a thin coating of clean oil to the
new seals to ease installation and prevent scuffing of
the sealing surfaces.
8. If the cylinder utilizes a teflon piston seal, special
care must be taken when installing the new seal. Tef-
lon seals are not as elastic as rubber or urethane
seals. Teflon seals should not be stretched exces-
sively because they may break or the cross section
may be permanently reduced to the point that the
teflon ring may not seal. One suggested method of
installation is to work about half of the seal into the
groove with a shoe string or fat nylon tie looped
inside the rings inside diameter. The string or tie can
be used to lift and guide the teflon ring into the
groove (the o-ring expander ring must be installed
first). When the teflon ring is nearly all the way in the
groove, the string or tie can be pulled free. Warming
the teflon ring will make it more pliable and will ease
the installation process. Once the teflon seal is posi-
tioned in the groove it must be resized so that it is
uniform contact with the o-ring expander under-
neath. This can be accomplished with properly sized
piston ring compressor. If equipment and material
are available, a cone shaped resizing die could be
fabricated for installation purposes.
9. Assemble the guide and piston on the rod. Be sure
to slip the retaining plate (if used) and snap ring on
the rod ahead of the guide and piston if they cannot
pass over the rod mount. Install and tighten the pis-
ton nut to required torque.
10. Apply a light coating of clean oil to the piston and
guide O.D. and mouth of the cylinder barrel. Care-
fully insert the piston into the wall and push the rod
assembly into the bore. When the piston is located
approximately half way down the bore, carefully
position the rod guide with the barrel mouth and
push the guide down the bore so that the front face
of the guide clears the snap ring groove. Be careful
not to mar the chromed rod surface. The guide may
have to be driven down the bore with a punch or
wooden dowel and hammer. Install the rod guide
retaining snap ring and be certain that it is nested
into the bottom of the groove all around. Install the
outboard retaining plate or spiral ring if used.
11. Check cylinder for external leaks using rated
hydraulic pressure. any leaks should be evident
after the cylinder has been pressurized for one min-
ute. Remove Pressure from cylinder. If the seals are
oil tight, the cylinder is ready for service.
KEEP AWAY FROM JETS OF HIGH PRESSURE OIL. HIGH PRES-
SURE OIL JETS CAN PENETRATE SKIN AND CAUSE SEVERE
INJURY OR DEATH.