6L80 and 6L90 transmissions often suffer failure of the 4-5-6 clutch assembly due to flexing and bowing of the backing plate (coning), especially when clutch apply pressures exceed OE specification. The heavy-duty Sonnax 4-5-6 clutch backing plate 104140A-01 is designed to minimize flexing/bowing when the clutch is applied, drastically reducing the likelihood of clutch plate distortion.