Pontiac FIREBIRD 1972 Service Manual page 350

1972 PONTIAC SERVICE MANUAL
a. Measure production spacers (Fig. 4A-39), and
subtract .004" from each reading. Do not mix the
left and the right spacers.
b. Using a service spacer (. 170") and service shims
make up a shim pack for each side equal to the
thickness of the original shim minus ,004" and
install as shown in Fig. 4A-40 and 41 (flat edge
of spacer against housing). This will duplicate the
original setting minus pre-load.
c. If this does not provide the proper slip fit, shims
must be added or removed equally from both
sides as necessary.
C AUTI 0 N: If insertion of shims causes exces-
sive pinion to ring gear contact (noticeable dif-
ficulty in rotation of the case), select thinner left
shim and add difference to the right side. Keep
total shim thickness at a value equal to that
obtained in step 3.
NOTE: Original light drag is caused by weight
of the case against the carrier while additional
drag is caused by side bearing preload.
For convenience in setting backlash and tooth
contact, the preload will not be added until the
final step.
4. Check backlash and tooth pattern as described in the
following section. The bearing caps must be installed
and the bolts torqued to 70 lb. ft.
5. When backlash and tooth pattern operations are
complete, remove shim packs taking care not to mix
them. Select new shim packs for each side ,004"
thicker than those removed and install each shim
pack on its proper side. This additional thickness will
provide proper bearing preload. It will be necessary
to tap the final shim into place with a soft hammer
or with BT 6623 (A and G Series) (Fig. 4A-42).
ADJUST DIFFERENTIAL BACKLASH
Rotate differential case several times to seat bearings,
then mount dial indicator (Fig. 4A-43). Use a small
button on indicator stem so that contact can be made
near heel end of tooth. Set dial indicator so that stem
is, as nearly as possible, in line with gear rotation and
perpendicular to tooth angle for accurate backlash
reading.
With pinion locked to carrier, check gear lash at 3 or
4 points around ring gear. Lash must not vary over
.002" around ring gear. If variation is over .002",
check for burrs, uneven bolting conditions or dis-
torted case flange and make corrections as necessary.
Gear lash, at the point of minimum lash, should be
.005" to ,009" for all new gears. If original gear set
having a wear pattern is being reinstalled, original
gear lash should be maintained.
If gear backlash is not within specifications, correct
by increasing thickness of one differential shim and
decreasing thickness of other shim the same amount.
In this way, correct differential bearing preload will
be maintained. Shift .002" in shim thickness for each
.OO 1 " change in backlash desired. If backlash is .00 1 "
too much, decrease thickness of right shim .002" and
increase thickness of left shim .002". If backlash is
,002" too little, increase thickness of right shim .004"
and decrease thickness of left shim .004".
Fig. 4A-42 Tapping Final Shim into Place
Fig. 4 A - 4 3 Checking Ring Gear to Pinion Backlash