When the transmission must be disassembled for unit repair service, the rear nut must be removed by placing the transmission in gear while holding the nut and turning the input shaft to loosen and then removing the rear nut. GM-50859 is a splined socket designed to fit the input shaft, which is used with GM-51327 to both remove and reinstall the rear nut. Unapproved methods may damage the input shaft splines.