The ball joint allows the suspension to pivot when steering and to move up and down as road surfaces become rough or uneven.
Without the pivoting motion afforded by the ball joint, steering a vehicle would be impossible.
When a ball joint develops wear, it develops excess clearance. A worn ball joint may develop a creaking sound when the suspension moves up and down while driving on an uneven road surface.
To replace a worn ball joint, the wheel is removed and the ball joint is separated from the steering knuckle or suspension. Then, the hardware securing the ball joint to the steering knuckle or suspension is removed, and the ball joint is replaced.