universal joint housing that positions the balls. When both shafts are in line, that is, at an angle of 180 degrees, the balls lie in a plane that is 90 degrees to the shafts. If the driving shaft remains in the original position, any movement of the driven shaft will cause the balls to move one half of the angular distance. For example, when the driven shaft moves through an angle of 20 degrees, the angle between the two shafts is reduced to 160 degrees. The balls will move 10 degrees in the same direction, and the angle between the driving shaft and the plane in which the balls lie will be reduced to 80 degrees. This action fulfills the requirement that the balls lie in the plane that bisects the angle of drive.

Tripod Joint

A tripod or ball and housing CV joint consists of a spider, usually three balls, needle bearings, outer yoke, and boot. The inner spider is splined to the axle shaft with the needle bearings and three balls fitting around the spider. The yoke then slides over the balls. Slots in the yoke allow the balls to slide in and out and also swivel.

During operation, the axle shaft turns the spider and ball assembly. The balls transfer power to the outer housing. Since the outer housing is connected to the axle stub shaft or hub, power is sent through the joint to propel the vehicle.

CENTER SUPPORT BEARINGS

When two or more drive shafts are connected in tandem, their alignment is maintained by a rubber bushed center support bearing (fig. 5-10). The center support bearing bolts to the frame or underbody of the vehicle. It supports the center of the drive shaft where the two shafts come together.

A sealed ball bearing allows the drive shaft to spin freely. The outside of the ball bearing is held by a thick, rubber, doughnut-shaped mount. The rubber mount prevents vibration and noise from transferring into the operator's compartment.

A bearing similar to the center support bearing is often used with long drive lines, containing a single drive shaft. This bearing is called a PILLOW BLOCK BEARING. It is commonly used in drive lines that power auxiliary equipment. Its purpose is to provide support for the drive shaft and maintain alignment. When used at or near the center of the shaft, it reduces the whipping tendency of the shaft at high speed or when under heavy loads. The construction of pillow blocks varies. The simplest form is used on solid power takeoff drive shafts, which is no more than a steel sleeve with a bronze bushing.

DRIVE LINE MAINTENANCE

A drive line is subjected to very high loads and rotating speeds. When a vehicle is cruising down the road, the drive shaft and universal joints or constant velocity joints may be spinning at full engine rpm. They are also sending engine power to either the front or rear axle assemblies. This makes drive line maintenance very important.

The drive shafts must be perfectly straight and the joints must be unworn to function properly. If any component allows the drive shafts to wobble, severe vibration, abnormal noises, or even major damage can result.

Figure 5-10. - Center support bearing.