General Description - Pontiac FIREBIRD 1972 Service Manual

NON TYPE C DIFFERENTIAL 4A-7
carrier. The effects of bearing preloads are not readily
apparent on (hand loaded) red lead tests: however, these
adjustments should be within specifications before pro-
ceeding with backlash and drive pinion adjustments.
Backlash is adjusted by means of the side bearing adjust-
ing shims which move the entire case and ring gear assem-
bly closer to, or farther from, the drive pinion. (The
adjusting shims are also used to set side bearing preload.)
The position of the drive pinion is adjusted by increasing
or decreasing the shim pack between the pinion head and
inner race of rear bearing. The shim pack is used in the
differential to compensate for manufacturing tolerances.
Increasing shim pack thickness will move the pinion
closer to centerline of the ring gear; decreasing shim pack
thickness will move pinion farther away from centerline of
the ring gear.
EFFECTS OF BACKLASH ON TOOTH PATTERN
The terms "excessive" and "insufficient" refer to settings
which are greater than .009" or less than .005" as speci-
fied. With respect to tooth contact patterns, "excessive"
refers to backlash which, although less than .009", is more
than necessary to provide the desired pattern. Similarly,
"insufficient" refers to backlash which, although .005" or
more, is less than necessary to provide the desired pattern.
Provided the pinion is properly positioned, excess back-
lash will give a high heel pattern on both drive and coast
sides (Fig. 4A-2C). Decreasing backlash by moving the
case and ring gear assembly closer to the pinion will cause
the pattern to move toward the toe end and down toward
center of the tooth on both drive and coast sides.
Insufficient backlash, provided the pinion is properly posi-
tioned, will give a low toe pattern on both drive and coast
sides (Fig. 4A-2B). Increasing backlash will cause the pat-
tern to move toward the heel end and up toward top of the
tooth on both drive and coast sides.
EFFECTS OF PINION POSITION ON TOOTH
PATTERN
When the drive pinion is too far away from centerline of
the ring gear, the pattern will be a high heel contact on
drive side and a high toe contact on coast side (Fig. 4A-
2D), provided backlash is within specifications of .005" to
.009". Moving the pinion closer to center line of the ring
gear by increasing shim pack thickness will cause the high
heel contact on drive side to lower and move toward the
toe; the high toe contact on coast side will lower and move
toward the heel (Fig. 4A-2F).
When the pinion is too close to the ring gear, the pattern
will be a low toe contact on drive side and a low heel
contact on coast (Fig. 4A-2E), provided backlash is within
specifications of .005" to .009". Moving the pinion farther
away from the ring gear by decreasing shim pack thick-
ness will cause low toe contact on drive side to raise and
move toward the heel; low heel contact on coast will raise
and move toward the toe (Fig. 4A-2G).
GENERAL DESCRIPTION
NOTE:
Specific information on the "C' type
differential is found in Sections 4C and 4 0 .
The rear axle and differential is of modified Hotchkiss
drive construction, utilizing a hypoid ring gear and pinion
set as a means of transmitting power (torque) from the
propeller shaft through a differential and then to semi-
floating axle shafts.
The non type C differential, as described below, is used in
all A and G Series vehicles, except those equipped with the
455 cu, in. engine. An identical differential with larger
ring gear and internal components is also used in some B
Series Catalina vehicles equipped with the 400 cu. in.
engine. A and G Series vehicles with the 455 cu. in. engine,
all F and X Series vehicles and all other B Series vehicles
use the "C" type differential. Two rear axle housing upper
control arms and two lower control arms (Fig. 4A-3), with
rubber bushings at connecting pivot points, form the basic
links of the rear suspension. The functions of the lower
control arms are to maintain the axle in line relative to
frame and to oppose torque reaction of the rear axle. The
upper control arms control rear axle windup and maintain
lateral stability of the car on the axle.
The upper ends of rear coil springs are retained in seats
formed in the frame, while the lower ends ride on spring
pads welded to the housing just forward of the center line
of axle assembly on the A and G series and directly over
the center line of the axle housing on B Series models. F
Series vehicles and B Series station wagon models use
multiple leaf springs. F Series models utilize a staggered
shock absorber arrangement.
Direct-acting sealed shock absorbers are mounted with
upper ends inclined toward center of vehicle. Rubber
bumpers, inserted in a bracket on the rear axle, cushion
extreme downward movement of the frame and body.
All parts necessary to transmit power from the propeller'