The “D” clutch in ZF8HP55, ZF8HP70 and ZF8HP75 transmissions has a thin, stamped OE backing plate that allows flexing and bowing (coning) of the clutch pack. This wears the clutches unevenly, generating and concentrating extra heat which leads to clutch burnup. The result is slipping or no 4th through 8th and Reverse Gears, as well as ratio codes. Sonnax heavy duty “D” clutch backing plate 35570-75 is designed to prevent flexing when the clutch is applied, eliminating a leading cause of “D” clutch failure.