Abstract: A ball joint wear detector having an indicator cap carried by a cover underlying a ball of a ball stud member received in a housing member. The indicator cap has a fixed reference surface on an outer ring thereof and a movable indicator surface on a center cup in which an actuator is received which is yieldably urged into engagement with a polar portion of the ball by a membrane of resilient material interconnecting the cup and the outer ring of the indicator cap. When the ball joint is in use, the extent of the axial displacement of the ball relative to the housing due to in-service wear of the ball joint is indicated by the displacement of the indicator surface relative to the fixed surface of the indicator cap which may be visually observed from the exterior of the ball joint.