manufacturers have clearance adjustment kits, consisting
of snap rings or pressure plates of varying thicknesses.
Replacing a snap ring or pressure plate with one of a
different thickness will change the clearance.
Clutch clearance is an indicator of how tightly the
plates and discs are packed. This is important because it
affects transmission operation. If the clearance is too large,
the clutch will not be applied tightly and may slip. If the
clearance is too small, the shift may be rough or the clutch
may be lightly applied when it should be released. Proper
clearance helps ensure good shifts and long clutch life.
Clutch pack operation can often be checked with
compressed air, Figure 17-27. Air is directed to the fluid
inlet port of the clutch, applying the piston. Piston action
can be observed to verify that the clutch will operate when
installed in the transmission.
Repeat the clutch pack rebuilding sequence for every
clutch pack in the transmission.
Band Service
Check band friction linings for overall wear. Look
for burn marks, glazing, and nonuniform wear. See
Figure 17-28. Check to see that grooves are still visible
and check for flaking. If any material can be scraped off,
the band should be replaced. Look for cracks or embedded
metal particles. Also, check bands for cracked ends,
broken ears, or distortion. See Figure 17-29. Bands
showing signs of wear or damage must be replaced.
The drum surface that the band rides on should also
be inspected. If the surface shows signs of severe scoring,
overheating, or wear, the drum should be replaced; slightly
worn drums can be turned down on a lathe. If the surface
must be turned down more than a few thousandths of an
inch (hundredths of a millimeter) to remove scoring or
wear, the clutch drum or gearset member that the band
rides on should be replaced. A surface that is shiny must
be sanded with emery cloth to remove the shine. Some
drums should be sanded around the surface perimeter,
while others should be sanded in an up-and-down direc-
tion. Check the appropriate service literature to determine
the direction in which the drum should be sanded. A new
band should always be used when the band’s mating
surface has been sanded.
Chapter 17 Rebuilding Automatic Transmissions and Transaxles 411
Caution: Never apply air pressure to the
clutch piston unless the clutch plates and
friction discs are installed. If the plates and
discs are not installed, air pressure may push the
piston far enough to jam it in its bore.
Air nozzle
Bench
test clutch
Air hose
Figure 17-27. Clutch pack operation should be checked with air
pressure before transmission assembly. This will ensure that
the clutch pack operates properly when it is installed.The clutch
plates and friction discs should lock together when air is applied
to the proper passage. (Subaru)
Figure 17-28. The friction material has worn away on the edge
of this band. The band must be replaced.
Figure 17-29. When servicing bands, be sure to check the
drum surface that the band rides on for signs of scoring, over-
heating, and wear. Note that the surface of this drum has been
sanded to remove the shine.
Caution: Soak new bands in clean ATF for
about 15 minutes or until they stop
bubbling. Always use the correct fluid.