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 effort.

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 dead axle.

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 connects.

There are three types of live axles used in automotive and construction equipment. The y are as follows: semifloating, three-quarter floating, and full-floating.

Semifloating Axles

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.