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.

FRONT-WHEEL DRIVE (AXLES)

Front-wheel drive axles, also called axle shafts or front drive shafts, transfer power from the transaxle differential to the hubs and wheel of a vehicle. Front- wheel drive axles turn much slower than a drive shaft for a rear-wheel drive vehicle. They turn about one third slower. They are connected directly to the drive wheels and do NOT have to act through the reduction of the axle ring gear and pinion gears.

Front-wheel drive axles typically consists of the following:

INNER STUB SHAFT - the short shaft splined to the side gears in the differential and connected to the inner universal joint.

OUTER STUB SHAFT - the short shaft connected to the outer universal joint and the front-wheel hub.

INTERCONNECTING SHAFT - the center shaft that fits between the two universal joints.

Universal joints that connect the drive axle are called CV joints. The outer CV joint is a FIXED (nonsliding) ball and cage or Rzeppa-type joint that transfers rotating power from the axle shaft to the hub assembly. The inner CV joint is called a PLUNGING (sliding) ball and housing or tripod-type joint that acts like a slip joint in a drive shaft for a rear-wheel drive vehicle.

Figure 5-26. - Constant velocity universal joints.

The plunging action of the inner CV joint allows for a change in distance between the transaxle and the wheel hub. As the front wheels move up and down over bumps in the road, the length of the drive axle (inner joint) must change.

REAR AXLE SERVICE

Rear axle service is needed when an axle bearing is noisy, when an axle is broken, bent, or damaged, or when an axle seal is leaking. The rear axles must be removed to allow removal and repair of the differential assembly.

Axle Bearing Service

Worn or damaged bearings in the carrier or on the axles produce a CONSTANT whirring or humming sound. These bearings, when bad, make about the same sound whether accelerating, decelerating, or coasting. When diagnosing and repairing bearing failures, do the following:

Check the general condition of all parts during disassembly,, not just the most badly worn or damaged parts.