If you do not know the exact location of the center of rotation of your ball joints, this simple method will allow you to establish the true center. Place the BJ in a vise with the shaft pointing up. Rotate the shaft all of the way to the left and mark the centerline on the housing over a piece of masking tape. Then rotate the shaft all the way over to the other side of the housing and mark the centerline again. The intersection is the true center of rotation.