Ball Joint

It works like a hip joint: a steel ball in a socket, packed with grease and sealed with a rubber boot. On many cars the lower ball joint is part of the control arm and is replaced with it.

The ball rotates and tilts in its socket, allowing suspension travel and steering movement at the same time.

A worn ball joint knocks over bumps and can make the steering wander. If it separates, the wheel can collapse, so play found at inspection should be fixed quickly.