4L60/4L60E/4L65E/4L70E Sonnax input drum reinforcement kit. This kit comes with reinforcement sleeve ,overrun piston, inner seal ,overrun piston ,overrun piston outer seal. The GM 4L60, 4L60-E, 4L65-E and 4L70-E input drum assembly is known to crack where the input shaft is pressed into it (where the overrun piston rides). Sonnax offers a hardened steel sleeve that reinforces the input drum to prevent this failure. Sonnax input drum reinforcement kit 77733-51K includes a custom manufactured overrun piston that is designed to be used only with a stamped steel forward piston, eliminating the need to use OE cast forward pistons or aftermarket billet forward pistons. Includes a custom manufactured overrun piston Compatible with stamped steel forward pistons Can be installed in early- and late-model units Sleeve made from hardened chrome steel sleeve design will not block clutch feed oil. WARNING: This kit must be used with a 97-later stamped steel forward piston, it cannot be used with '96-earlier aluminum forward piston or Sonnax billet forward piston 77764-01.