Chevrolet Light Duty Truck 1973, Service Manual

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REAR S U S P E N S IO N A N D DRIV ELINE 4-21
Differential Operation
A differential is an arrangement of gears that divides the
torque between the axle shafts and allows them to rotate
at different speeds. A basic differential consists of a set
of four gears. Two of these gears are called differential
side gears, and the other two are differential pinion
gears. Some differentials have more than two pinion
gears. Each side gear is splined to an axle shaft.
Consequently, each axle shaft must turn when its side
gear rotates.
The differential pinion gears are mounted on a
differential pinion shaft, and the gears are free to rotate
on this shaft. The 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 pinion roates the ring gear. The ring gear, being
bolted to the differential case, rotates the case. The
differential pinion, as it rotates with the case, forces the
pinion gears against the side gears. When both wheels
have equal traction, the pinion gears do not rotate on the
pinion shaft because the input force on the pinion gear
is equally divided between the two side gears. See figure
40. 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 41. To
prevent tire scuffing and sliding, the differential becomes
effective and allows the axle shafts to rotate at different
speeds.
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Fig. 41—Need for Differential Action
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 maintaining equal
speeds of rotation of the axle shafts. See figure 42. If the
vehicle speed remains constant and the inner wheel slows
to 90% of vehicle speed, the outer wheel speeds up to
110%. If the inner wheel slows to 75%, the outer wheel
would turn 125%. If one wheel stopped, the other wheel
would turn 200%.
BEARINGS
General Information
Roller bearings are precision products. Component parts
are carefully machined, heat treated and ground to
exacting tolerances and high surface finishes to provide a
maximum service life.
When properly installed, they demonstrate unusual
resistance to wear, heavy loads and difficult usage.
Despite their ruggedness, they are susceptible to
LIGHT DUTY TRUCK SERVICE MANUAL