Sonnax reinforced OE input housing and heavy duty input shaft kit 77733-13K is a great upgrade for GM 4L60, 4L60-E high performance and heavy-duty applications. The shaft is made of specially heat-treated steel with very hard outer layers and a more ductile inner core for strength and resistance to fracture. Feed holes are chamfered to reduce stress and the shaft is further processed by shot peening and deep cryogenic treatment. The high-strength 298mm style input shaft and OE housing comes with a reinforcement sleeve installed on the housing to strengthen the aluminum splines, which are otherwise prone to cracking. This kit 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 piston or aftermarket billet forward piston. For greater levels of performance, Sonnax offers a Smart-Tech® input housing kit with heavy duty input shaft, 77733-11K, that features additional input housing and 3-4 upgrades. NOTE: Fits 298mm units only All new drum and high-strength shaft assembly 57% harder than standard OE shaft Compatible with stamped steel forward pistons Reinforced input drum