Ball joints are swivel connections mounted in the outer ends of the front control arms, and on the steering track rods and tie-rods.
They allow the control arms to move up and down with suspension deflection, and also let the wheel and hub assembly turn for steering.
The ball joint can be a sealed, self-contained unit, fastened to the control arm in a number of ways.
It is made up of a pressed-steel housing, fitted with sintered iron seats, and a hardened ball stud. A taper on the stud locates in a mating taper on the suspension unit, and a rubber seal keeps out dirt and water.
Some ball joints can be dismantled, to replace the seats and the ball stud, and allow for adjustments. Shims between the upper and lower halves of the joint allow free play to be controlled.
Grease nipples can allow for periodic lubrication but most joints to-day are sealed for life, and no regular maintenance is required. On tie-rod ends, the ball joint is usually self-contained and attached to the tie-rod by internal or external threads.
