Outer ball joint (control arm to wheel carrier). 2 per car. Ball joints connect the steering knuckles to the control arms. The ball joint itself is a flexible ball and socket that allows the suspension to move and the wheels to steer in all directions. Ball joints will eventually wear out and become loose, just like any other suspension component on your car, which can affect tire wear and wheel alignment. Ball joint wear can also cause a clunking noise when going over a bump. If not properly maintained, a ball joint failure can lead to suspension collapse. Make sure your ball joints are properly lubricated (no torn boots) during front end service and replace them immediately if you notice excessive wear and tear.