Front drive axle

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Rear drive axle

Construction Mechanic Basic Volume 2

Front-wheel drive axles

FRONT DRIVE AXLE
A front drive axle (fig. 5-25) is very similar to a rear drive axle; however, provisions must be made for steering the front wheels. Power is transmitted from the transfer case to the front axle by a drive shaft. The differential housing may be set off center in the axle housing to permit the drive shaft to pass beside the engine oil pan and maintain sufficient road clearance without excessive height at the front end of the vehicle.

Since the front wheels must turn on the spindle arm pivots, they must be driven by the axle shaft through universal joints, which are located on the outer ends of the axles. The universal joints allow the front wheels and hubs to swivel while still transferring driving power to the hubs and wheels.

The cross and roller joint shown in figure 5-25 is similar to conventional U-joints used on the rear drive shaft, and, in some cases, they are interchangeable.

Figure 5-25.- Front drive axle.

This type of U-joint is limited to use in light-duty, vehicles. Other types of universal joints are used in the axles of heavy-duty vehicles. The types you will encounter in military designed vehicles are the Rzeppa and Bendix-Weiss constant velocity joints (fig. 5-26).

The front drive axle of a four-wheel drive axle requires locking hubs. Locking hubs transfer power from the driving axles to the driving wheels on a four-wheel drive vehicle. There are three basic types of locking hubs, which are as follows:

MANUAL LOCKING HUB- requires the operator to turn a latch on the hub to lock the hub for four-wheel drive action.

AUTOMATIC LOCKING HUB- hub locks the front wheels to the axles when the operator shifts into four-wheel drive.

FULL TIME HUB- front hubs are always locked and drive the front wheels.

Manual and automatic locking hubs are the most common. Used with part-time, four-wheel drive. they enable the drive line to be in two-wheel drive for use on dry pavement. The front wheels can turn without turning the front axles. This allows for increased fuel economy and reduces drive line wear.