example, one wheel is on ice and the other wheel is on
dry pavement. The wheel on ice is assumed to have no
traction. However, the wheel on dry pavement will pull
to the limit of its tractional resistance at the pavement.
The wheel on ice cannot spin because wheel speed is
governed by the speed of the wheel applying tractive
The no-spin differential does not contain pinion
gears and side gears as the conventional differential
does. Instead, it consists essentially of a spider attached
to the differential drive ring gear through four trunnions,
plus two-driven clutch members with side teeth that are
indexed by spring pressure with side teeth in the spider.
Two side members are splined to the wheel axles and,
in turn, are splined into the driven clutch members.
The first hint of existing trouble in a differential is
generally an unusual noise in the rear axle housing.
However, to diagnose the trouble properly, you must
determine the source of the noise and under what
operating conditions the noise is most pronounced.
Defective universal joints, rough rear wheel bearings, or
tire noises may be improperly diagnosed by the
inexperienced mechanic as differential trouble. Some
clue may be gained as to the cause of trouble by your
noting whether the noise is a growl, hum, or knock;
whether it is hard when the car is operating on a straight
road, or on turns only; and whether the noise is most
noticeable when the engine is driving the vehicle or
when it is coasting with the vehicle driving the engine.
A humming noise in the differential generally
means the ring gear or pinion needs an adjustment. An
improperly adjusted ring gear or pinion prevents normal
tooth contact between the gears and, therefore, produces
rapid gear tooth wear. If the trouble is not corrected
immediately, the humming noise will gradually take on
growling characteristics, and the ring gear and pinion
will probably have to be replaced.
It is easy to mistake tire noise for differential noise.
Tire noise will vary according to the type of pavement
the vehicle is being driven on, and differential noise will
not. To confirm a doubt as to whether the noise is caused
by tire or differential, drive the vehicle over various
types of pavement.
If a noise is present in the differential only when the
vehicle is rounding a cornr, the
in the differential case assembly.
trouble is likely to be
AXLES, WHEELS, AND TRACKS
A live axle may support part of the weight of a
vehicle and also drive the wheels connected to it. A dead
axle carries part of the weight of a vehicle but does not
drive the wheels. The wheels rotate on the ends of the
Usually, the front axle of a passenger car is a dead
axle, and the rear axle is a live axle. In four-wheel drive
vehicles, both front and rear axles are live axles, and in
six-wheel drive vehicles, all three axles are live axles.
The third axle, part of a BOGIE DRIVE, is joined to the
rearmost axle by a trunnion axle, as shown in
figure 11-20. The trunnion axle is attached rigidly to the
frame. Its purpose is to help in distributing the load on
the rear of the vehicle to the two live axles which it
There are three types of live axles used in
automotive and construction equipment. The y are as
semifloating, three-quarter floating, and
The semifloating axle (fig. 11-21) used on most
passenger cars and light trucks has its differential case
independently supported. The differential carrier
relieves the axle shafts from the weight of the
differential assembly and the stresses caused by its
operation. For this reason, the inner ends of the axle
shafts are said to be floated. The wheels are keyed or
bolted to outer ends of axle shafts, and the outer bearings
are between the shafts and the housing. Therefore, the
rude shafts, must take the stresses caused by turning or
skidding of the wheels. The axle shaft in a semifloating
live axle can be removed after the wheel and brake drum
have been removed.
Three-Quarter Floating Axles
The axle shafts in a three-quarter floating axle
(fig. 11-22) may be removed with the wheels that are
keyed to the tapered outer ends of the shaft. The inner
ends of the shafts are carried as in a semifloating axle.
The axle housing, instead of the shafts, carries the
weight of the vehicle because the wheels are supported
by bearings on the outer ends of the housing. However,
axle shafts must take the stresses caused by the turning,
or skidding of the wheels. Three-quarter floating axles
are used in some trucks but in very few passenger cars.