Universal Joint (U-joint)

It uses a cross-shaped spider with needle bearings. It is common on propeller shafts and steering columns. Some are greased, others sealed. A single U-joint does not turn at constant speed when angled, so pairs are arranged so the speed variations cancel. Grease points should be lubricated where present. Replacement requires pressing out the old bearing caps carefully. Correct phasing of the joints on the shaft matters for smooth running.

The spider pivots in its bearings as the shafts rotate at an angle.

Worn U-joints cause clunks, squeaks and vibration. Rust-coloured dust around the caps is a warning sign.