Rear Axle - Chevrolet 1977 light duty truck Service Manual

The following caution applies to one or more steps in the assembly
procedure o f components in this portion o f the m anual as indicated at
ap pro priate locations by the terminology "See Caution on Page 1 o f this
Section".
C A U TIO N :
P A R T I N T H A T I T C O U LD A F F E C T T H E P E R F O R M A N C E OF
V IT A L C O M P O N E N T S A N D S Y S T E M S , A N D / O R C O U L D R E S U L T
I N M A J O R R E P A I R E X P E N S E . I T M U S T B E R E P L A C E D W I T H
O N E OF T H E S A M E P A R T N U M B E R OR W IT H A N E Q U I V A L E N T
P A R T I F R E P L A C E M E N T B E C O M E S N E C E S S A R Y. D O N O T U S E A
R E P L A C E M E N T P A R T OF L E S S E R Q U A L I T Y OR S U B S T I T U T E
D E S IG N .
D U R I N G R E A S S E M B L Y TO A S S U R E P R O P E R R E T E N T I O N OF
T H I S P A R T .
G en eral D escriptio n......................................................................... 4B-1
Differential D iagnosis.......................................................................4B-7
G e n e ra l Diagnostic P ro c e d u re .................................................. 4B-10
Differential and Rear Axle Bearing D iagnosis.................. 4B-11
On-Vehicle Service............................................................................... 4 B -13
8 -1 /2 " and 8 -7 /8 " Ring G e a r ................................................. 4B-13
Chevrolet 10-1/2" Ring G e a r ................................................... 4B-18
D a n a 10-1/2" Ring G e a r ........................................................... 4B-21
D an a 9 -3 /4 "R in g G e a r ............................................................... 4B-21
Chevrolet 12-1/4" Ring G e a r ................................................... .4B-21
Specifications....................................................................................... 4B-24
Special T ools........................................................................................4B-25
A differential is an a rra n ge m ent o f gears that
divides the torque between the axle shafts and allows
them to rotate at different speeds. A basic differential
consists o f a set o f four gears. Two o f these gears are
called differential side gears, an d the other two are
differential p inion gears. Some differentials have more
than two pinion gears. Each side gear is splined to an
axle shaft. Consequently, each axle shaft must turn w hen
its side gear rotates.
T h e differential pinion gears are mounted on a
differential p inion shaft, and the gears are free to rotate
on this shaft. T he pinion shaft is fitted into a bore in the
differential case and is at right angles to the axle shafts.
Power flow through the differential is as follows:
The drive p inion roates the ring gear. The ring gear,
being bolted to the differential case, rotates the case. The
differential pinion, as it rotates w ith the case, forces the
pinion gears against the side gears. W hen both wheels
have equal traction, the pinion gears do not rotate on the
pinion shaft because the input force on the pinion gear
SECTION 4B

REAR AXLE

T H I S F A S T E N E R I S A N
T O R Q U E V A L U E S M U S T B E
C O N T E N T S
GENERAL DESCRIPTION
I M P O R T A N T A T T A C H I N G
U S E D A S S P E C IF IE D
is equally divided between the two side gears. See figure
4B-1. Consequently, the pinion gears revolve with the
pinion shaft, but do not rotate around the shaft itself.
The side gears, being splined to the axle shafts and in
mesh with the pinion gears, rotate the axle shafts.
If a vehicle were always driven in a straight line, the
ring and pinion gears would be sufficient. The axle shaft
could then be solidly attached to the ring gear and both
driving wheels would turn at equal speeds.
However, if it became necessary to turn a corner, the
tires would scuff and slide because the outer wheel would
travel further than the inner wheel, as in figure 4B-2. To
prevent tire scuffing an d sliding, the differential becomes
effective and allows the axle shafts to rotate at different
speeds.
As the inner wheel slows down, the side gear splined
to that axle shaft also slows down. At this point, the
pinion gears act as balancing levers by m aintaining
equal speeds o f rotation o f the axle shafts.See figure4B-3.
If the vehicle speed rem ains constant and the inner