Ball Joints — Types and Inspection

Ball joints are the pivot points that connect the control arms to the steering knuckle. They must allow the knuckle to pivot for steering input while simultaneously allowing it to move up and down with suspension travel. Think of them like the ball joints in your hip or shoulder — they allow rotation in multiple directions simultaneously.

Not all ball joints are the same type, and this matters for inspection. A load-bearing ball joint carries the weight of the vehicle corner. The spring loads it. These joints wear fastest because they are constantly under load even when the vehicle is sitting still. A follower ball joint — also called a tension or non-load-bearing joint — is not loaded by the spring. It only positions the top of the knuckle and controls geometry. Different inspection procedures apply to each type.

A steel ball is machined to a precise diameter and sits inside a housing. Grease fills the space between the ball and housing to reduce friction and prevent wear. The ball has a tapered stud that passes through the control arm or knuckle and is secured with a nut. As the joint wears, the clearance between the ball and housing increases. When clearance exceeds specification, the joint must be replaced.

Never inspect ball joints with the wheels hanging free. Load the suspension in its normal operating position on a drive-on rack. For a load-bearing lower ball joint: place a jack under the lower control arm near the ball joint. Raise the lower arm slightly to unload the joint while keeping the tire on the rack. Grasp the tire at 12 and 6 o'clock and push in and out. Any vertical movement indicates ball joint wear. For a follower upper ball joint: with suspension loaded, grasp the tire and push in and out at 12 and 6 o'clock. Movement indicates wear. Movement specifications vary by manufacturer — always verify the maximum allowable play against the service manual before condemning a joint.

Some ball joints have grease fittings — also called Zerk fittings — that allow the joint to be lubricated during service. These should be greased at every oil change or at least annually. A ball joint without a grease fitting is a sealed joint meant to be lubricated for life. Sealed joints cannot be greased and must be replaced when worn. Never attempt to drill and install a grease fitting in a sealed joint.