Car Parts and Accessories

Housings for beam Automobile Axles

In recent years, there has been a swing from automobile rear to front-wheel drive for passenger cars although many manufacturers have retained rear-wheel drive for larger prestige models.

Most automobile which have front engines and rear-wheel drive are fitted with a rigid rear axle or beam axle. The half-shafts and final-drive assembly, which includes the differential, are enclosed by a rigid housing which contains automobile bearings to support the rotating parts.

Usually, it is only the more expensive automobile rear-drive models, or those with front- wheel drive and therefore no differential at the rear, which have independent automobile suspension on the back wheels.

There are two main types of automobile axle housing. In one, the banjo axle, the axle is a single unit and the final drive assembly is carried in a separate casing which is bolted to the axle housing. In the other, a central housing contains the final drive and is fitted with a tube at each side.

Support for the Automobile half-shafts

Axles are classified according to the way in which the half-shafts and wheel hubs are supported. In all types, the inner ends of the half-shafts are connected to the gears of the differential.

In the semi-floating axle each half-shaft is supported at its inner end by a bearing which also carries the final drive unit. At the outer end there is a bearing between the shaft and the inside of the axle housing. The half-shaft has to withstand bending loads imposed by the weight of the car, as well as transmit torque.

The three-quarter floating axle also has a bearing inside the axle housing which carries the final-drive unit, but the outer bearing is placed between the wheel hub and the axle housing, to support the weight of the car. The half-shaft is subjected to a bending load only during cornering.

In front-drive automobile and in independently sprung rear-drive automobile, each hub is supported by two bearings.

Coping with Automobile twisting forces

When power is transmitted to the automobile rear axle by an open propeller shaft, torque reaction twists the axle on its springs. This can be prevented by enclosing the propeller shaft in a torque tube, which forms a rigid extension of the automobile axle housing. The torque tube is bolted to the automobile axle housing and is connected to the gearbox at its front end by a large spherical bearing so that it resists the torque reaction.

Conventional automobile use a manual or automobilematic transmission to change ratios, a drive shaft which takes power to the differential and a pair of driven wheels. To improve automobile traction on rough or slippery surfaces, or to improve roadholding when used in sporting vehicles, the remaining two wheels can also be driven. With power available on four automobile wheels, the vehicle can cross rugged country where optimum traction is essential.

Four-wheel automobile drive vehicles may use constant or part-time engagement. Automobile which use constant four- wheel drive have a third differential, usually mounted in the middle, so the front and rear differentials can turn at different speeds. The primary automobile drive can be the rear pair of wheels, or the front wheels.

Part-time four-wheel drive vehicles have a central automobile gearbox to select the mode of driving and may have an alternative set of ratios so the automobile can move very slowly. A manual transmission transfer case gear lever will be printed with 2H, N, 4H, 4L. These relate to two-wheel drive high-range (normal driving), neutral (selected when a power take-off is being used for accessories such as a winch), four-wheel drive in high range (sandy or slippery conditions) and four-wheel drive low range (for steep or rocky conditions).

As the unused differential automobile turns even when power isn’t engaged, it may incorporate free-wheeling hubs. These can be manual or automatic and disconnect the differential (which is not used in two- wheel drive) from the road wheels.

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