JLG 680S, Service And Maintenance Manual, Page: 367 / 530

SECTION 5 - BASIC HYDRAULICS INFORMATION & SCHEMATICS
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STEER CYLINDER SEAL REPAIR INSTRUCTIONS
1. The cylinder should be disassembled in a clean environ-
ment to prevent dirt or other contamination from enter-
ing 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 disassembly, 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 suggested for resizing new teflon piston seals used in
some cylinders.
2. Secure in vise at approximately the mid-point of the cyl-
inder 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 capscrews 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 cyl-
inder 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 remov-
ing 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. Care-
fully cutting the seal apart with an Xacto knife will also
ease removal.
7. Inspect the seal grooves and clean away any contamina-
tion. Apply a thin coating of clean oil to the new seals to
ease installation and prevent scuffing of the sealing sur-
faces.
8. If the cylinder utilizes a teflon piston seal, special care
must be taken when installing the new seal. Teflon seals
are not as elastic as rubber or urethane seals. Teflon
seals should not be stretched excessively 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. Warm-
ing 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 uni-
form contact with the o-ring expander underneath. 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 installa-
tion 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 piston 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. Carefully 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 sur-
face. 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 minute. 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
PRESSURE OIL JETS CAN PENETRATE SKIN AND CAUSE
SEVERE INJURY OR DEATH.