Ball Joint Diagnosis and Repair
Ball joints fasten the spindle to the control arm, providing a pivot point for steering and movement as the vehicle travels over bumps in the road. A worn ball join will reveal itself as a thunking or popping noise that occurs when the vehicle hits a bump in the road or when turning the wheel at low speeds.
Some ball joints contain a wear indicator. The grease fitting extends out from the base of the joint. As the ball joint wears the fitting recesses into the base of the ball joint. On some ball joints the grease fitting will feel loose in the base. If either of these conditions are notices the ball joint should be replaced.
Not all ball joints have wear indicators though. You can tell if it’s worn by measuring the up and down endplay of the ball stud in the seat. Like most end play measurements it is checked with a dial indicator and typically should not exceed .050”. This measurement is fairly straightforward with today’s passenger cars because they are mostly front wheel drive models that contain struts. Struts have the coil spring wrapped around the strut assembly and the spindle can be separated from the ball joint by removing the pinch bolt. Then the ball joint can be inspected.
If no wear indicator is present the ball joint must be unloaded to check endplay. This is because the coil spring is forcing the ball stud into the seat. The coil can be placed against the upper control arm or the lower control arm. If the spring is seated into the lower control arm a floor jack is placed under the control arm close to the ball joint and the tire is raised off the ground about two inches. If the coil is seated between the frame and the upper control arm the floor jack is placed under the frame before it is raised.
Conventional steering and suspension systems found on trucks often contain two ball joints; an upper and a lower. These ball joints are to be replaced in pairs; if the lower ball joint on one side is replaced the lower ball joint on the other side should be changed as well. If an upper ball joint is replaced on one side the upper ball joint on the other side should be changed as well.