JLG T350 Service Manual - Manual (Page 145)

SECTION 5 - HYDRAULICS
3121198 – JLG Lift – 5-3
5.2 CYLINDER REPAIR
Disassembly
DO NOT ATTEMPT TO SERVICE A HYDRAULIC CYLINDER WHILE
IT IS INSTALLED. THE CYLINDER MUST BE REMOVED FROM THE
MACHINE AND ALL PRESSURE MUST BE RELIEVED. AIR MUST
NOT BE USED TO EXTEND OR RETRACT THE CYLINDER. SAFETY
GLASSES MUST BE WORN AT ALL TIMES BY SERVICE PERSON-
NEL.
1. The cylinder should be secured in such a way as to
prevent rotation of the barrel while unscrewing the
head gland. Care should be taken to avoid damag-
ing the rod surface and to avoid excessive deforma-
tion of the barrel, which could permanently damage
the unit. Make sure to support the rod during
removal.
2. Remove all dirt, grease, and other contaminants
from around the ports and the head gland. Drain all
oil from the unit. Extending and retracting the rod
manually can help purge the bulk of the remaining
oil.
3. Mark the orientation of the rod, gland, and barrel
with a permanent marker or paint pen. Do not apply
any paint on the chromed surface of the rod.
Unscrew the head gland from the cylinder assembly
using a spanner wrench in the holes provided in the
OD of the head gland.
NOTE: The threads are locked with a non-permanent thread
adhesive during assembly. A quick tug on the
wrench may be necessary to release the thread
adhesive.
4. Remove the rod assembly from the barrel using care
not to damage the threads or any other component
surface.
5. Clamp the rod mount and support the rod assembly
with the chrome surface protected. Remove the pis-
ton assembly either by unthreading the locknut with
a socket wrench or the piston itself from the rod
using a spanner wrench depending on the cylinder
model.
Inspection
1. Inspect all seals, backup rings, wipers, and wear
rings for tears, grooves, foreign matter, and exces-
sive wear. Deep grooves may be an indication of
damage to the barrel bore, rod chrome, or the pres-
ence of large particle contamination.
2. Remove the seals, backup rings, wipers, and wear
rings using a soft metal tool (brass or aluminum)
with rounded edges. Use care not to nick or score
the surfaces of any component, especially the seal
grooves.
3. Wipe all components with a lint-free cloth. Plug the
barrel opening with a lint-free cloth. Remove any
adhesive remnants from the head gland, barrel, rod,
and piston threads (where applicable) using a soft
wire brush. Use care not to scratch or otherwise
damage the critical surfaces of any component
including seal grooves, barrel bore, rod chrome, etc.
4. Inspect the piston and head gland for excessive
wear, cracks, scoring, or any other damage. If wear
is present on the OD of the piston or the ID of the
head gland, check to ensure that the circularity of
both dimensions is within 0.007" (0.177 mm).
Beyond this limit the seal performance is compro-
mised and the components must be replaced.
5. If equipped, the stop tube should be inspected for
cracking and excessive flaring of the ends.
6. Closely inspect the chrome surface of the rod. Any
nicks, gouges, or scratches that penetrate the
chrome plating or result in a sharp edge, which may
damage seals, are cause for rod assembly replace-
ment.
7. Flush the barrel and fluid tube (if equipped), drain,
and wipe dry with a lint-free cloth. Closely inspect
bore for nicks, gouges, or scratches. Replace the
barrel assembly if any of these are present.