Design; Operation - Pontiac FIREBIRD 1972 Service Manual

4A-8 1972 PONTIAC SERVICE MANUAL
REBOUND BVUPE'I UPPER CONTROL ARM REBOIINO BUMPER 5 H O C I 4 8 S O R B I R
Fig. 4A-3 Typical Rear .Axle View
shaft to the rear wheels are enclosed in a salisbury type
axle housing (an iron casting with tubular axle housings
pressed and welded into the carrier to form a complete
carrier and tube assembly). A removable steel cover bolted
to the rear of the carrier permits service of the differential
without removing the rear axle from the car. Rear axle
shafts are mounted on roller bearings located at the outer
ends of the rear axle housing. Axle shaft bearings are of
two different types
-
unit and direct-on type. The unit
bearing, which is used in all standard differentials as de-
scribed in this section, consists of the bearing rollers and
an inner and outer race. The direct-on bearing, used in all
"C" type axles, is so named because it consists only of the
bearing rollers and an outer race. A machined surface on
the axle shaft serves as the inner race of the direct-on
bearing. The unit bearing assembly is pressed to a shoul-
der on the shaft and is additionally held in place by a
pressed-on inner retainer ring. An outer retainer, which
also clamps the brake backing plate to the axle housing,
secures the bearing in the end of the axle housing. All axle
shafts have outboard seals with roller bearings lubricated
by differential lubricant. Seals prevent oil seepage from the
axle housing into the wheel bearing cavity and onto the
brake assembly.
To prevent pressure build up, a breather vent is provided
at the right side of the axle housing.
DESIGN
Hotchkiss drive (open drive line) is the basic design used
to transmit power from the drive shaft to the rear wheels,
but the design is modified to include torque reaction links
(upper and lower control arms) rather than leaf springs.
A universal joint connects the end of the propeller shaft
to a companion flange, having a splined end which fits
over and drives the rear axle drive pinion gear. This com-
panion flange is securely fastened to the pinion shaft by a
special self-locking nut which bears against a special
washer.
Two preloaded tapered roller bearings support the drive
pinion gear in the carrier. The inner race of the rear bear-
ing is a tight press fit on the pinion stem. The inner race
of the front bearing combines a light press fit to a close
sliding fit on the companion flange end of the pinion stem.
The outer race of each bearing is pressed against a shoul-
der recessed in the carrier. Tightening the pinion nut com-
presses a collapsible spacer, which bears against the inner
race of the front bearing and a shoulder on the pinion
stem. This spacer is used to maintain a load on the front
bearing inner race and pinion stem and to prevent the
inner race of the front bearing from turning on the pinion
stem.
Adjustment of the pinion along its axis is obtained by
placing shims between the pinion rear bearing inner race
and the pinion gear. Torque from the pinion gear is trans-
mitted to a ring gear attached to a differential case by
special hex head bolts.
The differential is a device that divides the torque equally
between axle shafts. It permits the rear wheels to turn
together at the same speed, or to turn at different speeds,
as when making turns, etc. It is so designed that it will
exert force to the wheel having the least traction.
The differential case is of one piece construction. Two side
gears and two pinion gears are housed in the case. The two
side gears have splined bores for indexing with and driving
the axle shafts. They are positioned to turn in counter-
bored cavities in the case. The two differential pinion gears
have smooth bores and are held in position by a solid
pinion cross shaft, mounted and locked in the differential
case. All four gears are in mesh with each other and
because the pinion gears turn freely on their shaft, they act
as idler gears when the rear wheels are turning at different
speeds.
OPERATION
Power from the engine is transferred to the transmission
via a clutch, or a fluid coupling with an automatic trans-
mission. The transmission then provides the transfer of
power to its output shaft, which is splined to the propeller
shaft by means of a universal joint connection. Since the
rear of the propeller shaft is connected to the differential
pinion gear at the companion flange, the transmission
output shaft, propeller shaft and differential pinion all
turn at the same speed.
Power from the pinion gear is transmitted to the differen-
tial ring gear which is bolted to the differential case. When
there is equal resistance on each rear wheel, the force
through the pinion and ring gear turns the axle shafts at
the s a d e rate of speed and there is no movement between
differential pinions and side gears.
When the vehicle turns a corner, the outer rear wheel must
turn faster than the inner one. The inner wheel, turning
slower with respect to the outer wheel, slows the differen-
tial side gear (as the axle shaft is splined to the side gear)
and the differential pinion gear will roll over the slowed