often jar the piston loose. Compressed air can also be used
to blow the piston from the drum. Place the drum down-
ward on the workbench and insert an air nozzle in the oil
feed hole in the center of the drum. A short burst of air
should push out the piston.
With the piston out of the drum, remove the piston
seals. Hard or cracked seals indicate that the clutch has been
overheated. If there is also a seal around the interior (hub) of
the clutch drum (inner piston seal), remove it, Figure 17-23.
Then, thoroughly clean the piston and piston bore.
Often, clutch apply pistons and clutch assemblies are
installed in the rear of the case. Disassembly and assembly
procedures for these assemblies are similar to those for
other clutch packs.
Inspect the piston for cracks. Also check that the air
bleed check ball is free.
Obtain new piston seals. Compare the new seals to the
old ones to ensure that you are installing the proper seals
on the piston. In addition, check the fit of the new seals by
placing them in the piston bore. They should fit snugly. A
bulge, or buckle, in an outer piston seal means the seal’s
diameter is too large. A gap between an outer piston seal
and the piston bore means the diameter is too small.
Before installing the new piston seals, lubricate them
with transmission fluid. Petroleum jelly can also be used,
but other types of oil or grease will damage the seals.
Carefully install the new piston seals on the clutch drum
hub and clutch piston, as applicable. The new seals should
fit snugly, but not too snugly. Lip seals must be installed on
a piston so the sealing lip will be directed toward the
hydraulic pressure (toward the back of the drum).
Install the clutch piston in its bore. The type of piston
seal determines the installation method. If O-ring seals are
Chapter 17 Rebuilding Automatic Transmissions and Transaxles 409
Return
springs
Compressor
tool
Remove
piston
snap ring
Figure 17-21. A special compressor must be used to remove
the clutch apply piston in order to get at the seals of the clutch
assembly. Universal tools are available that fit all types of
assemblies. (DaimlerChrysler)
Snap ring
Spring
retainer
Piston
O-ring
Return spring
Drum
assembly
Figure 17-22. Exploded view of a clutch apply piston and
related parts shows parts that must be removed during
rebuilding. (Nissan)
Warning: When using compressed air to
remove a piston, point the open end of the
drum away from yourself and others. Direct
the piston into a pile of rags or another soft surface
so that it does not fly out and become damaged or
cause injury. Also, use a regulated amount of air
pressure.
Note: If the check ball is missing, do not
attempt to install a replacement check ball.
Replace the apply piston.
Figure 17-23. Inner piston seals can usually be removed
with a small pick. Inspect the seals carefully for damage and
excessive wear.