Existing retaining rings are not strong enough to withstand slight radial movement of the pressure plate, which walks the retaining ring out of its groove.
Replace the low/reverse retaining ring with the heavy duty Sonnax version, which is wider and stiffer than other rings and provides more outward spring tension to stay securely seated in the case groove.
A common failure in the Ford 5R110W occurs when the low/reverse retaining ring pops out of the case groove, causing slips in reverse and severe damage to the case lugs. When moving in reverse, the pressure plate can have some radial movement in the case. This movement walks the retaining ring out of its groove. Sonnax low/reverse retaining ring 36885 is wider and slightly thicker, providing more outward tension than other available replacement rings. The increased tension and extra stiffness help keep the ring seated securely in the case groove. This retaining ring can be used in both gas and diesel applications.