ZF S6-650 Input Shaft 23-Tooth 10-3/8 in Ford 6-Speed

This is a new replacement input shaft for the ZF S6-650 six-speed manual, the transmission Ford ran behind the 7.3L Power Stroke and the V10 in F-250, F-350 and F-450 trucks from 1998 up. It measures 10-3/8 inches long and carries 23 splines on the clutch end, matching the factory shaft so the original disc, pilot bearing and bearing retainer all go back on without modification.

The input shaft is one of the parts that gets scrapped during a S6-650 teardown rather than reused. The usual reasons are worn or chipped clutch splines from a slipping or badly adjusted disc, a grooved seal surface at the retainer, a galled pocket bearing bore, or blued and pitted 4th gear cone from running the box low on lubricant. Any one of those means the shaft comes out and a new one goes back in, because a worn spline will chew through a brand new clutch disc in short order.

On the bench it installs the same way the original came out: press the front bearing off the old shaft, transfer or replace the pocket bearing, set the shaft into the case with the 4th gear synchro assembly, then reinstall the bearing retainer with a fresh seal. Check input shaft endplay before the case halves go back together. Plan on replacing the pocket bearing and front seal at the same time - they are cheap and they are already exposed.