Joint yoke for Audi 100

Nut, constant-velocity joint, tripod: what do they do?

A driveshaft must rotate at a constant speed even though its two ends are never aligned: the wheel turns and the suspension moves. This is the role of the constant-velocity joint, which transmits torque smoothly regardless of the angle, unlike a simple cross-type universal joint.

• The universal joint is the component that provides this connection: a cage, balls and machined raceways, all enclosed in a grease-filled bellows.
• The tripod housing is the other technical solution, featuring three rollers, which also allows for axial sliding. It is generally found on the gearbox side, where the shaft needs to be able to extend.

In everyday usage, the three terms are often used interchangeably. Technically, the tripod housing slides and the ball joint steers.

Wheel side and gearbox side: two different components

A drive shaft carries a joint at each end, and they do not operate in the same way.

• On the wheel side, the joint is subjected to the steering angles, which are the most significant. It is this joint that rattles when worn, and it is the one most often replaced.
• On the gearbox side, the angle is small but the joint must slide to absorb changes in length caused by suspension travel. Wear on this joint manifests as vibration rather than a clunking noise.

They are never interchangeable, and their dimensions differ even on the same vehicle. You should therefore always check the side before ordering, and note it down from the part you have removed rather than guessing.

Recognising a joint at the end of its service life

• A repetitive clacking noise when turning the steering wheel at low speed, more pronounced on one side: worn outer bushing, on the wheel side. The noise follows the rotation of the wheel and disappears when driving in a straight line.
• A vibration when accelerating, which subsides when you lift off the accelerator: this is more likely to be the joint on the gearbox side, or the tripod mount no longer sliding freely.
• A jolt when setting off, as if clearing play: wear on the splines or the housing.
• Grease sprayed onto the wheel arch and the inside of the rim: the grease seal is punctured, and the rest is a foregone conclusion.

The boot decides everything

A universal joint almost never wears out on its own. It fails because its boot has split. As soon as the tear appears, the grease escapes due to centrifugal force, and water, dust and salt get in. Within a few hundred kilometres, the raceways are pitted and the part is ruined.

Checking the boots every time you work under the car, with the wheels turned fully to one side to inspect the folds, is therefore the most cost-effective way to check the front suspension. A boot replaced in good time costs a fraction of the price of a complete ball joint. If replaced too late, it won’t save anything: fresh grease cannot repair balls that are already worn.

What to note before ordering

• The side of the shaft – gearbox or wheel – and the side of the vehicle – left or right: the lengths almost always differ.
• The outer diameter of the hub, in millimetres, which is the reference dimension for these parts.
• The number of splines on the shaft, to be counted on the part being removed: this is the feature that distinguishes two parts that look identical.
• The type of transmission and the shaft diameter, which vary depending on the engine specification of the same model.

Order the complete kit where available, including the boot, clamp, suitable grease and retaining rings. Fitting a new steering knuckle with a worn original boot means you’ll have to do the job all over again the following year.