The shaft size and style for all 3 cases are different and not interchangable. I've always remembered them by the letters, but I'm pretty sure the "X" (741?) carrier is 1.375" shaft, "9" (742?) carrier is 1.75" shaft, and the "2" (489?) carrier is 1.875" shaft. Someone please correct me if wrong. I just remembered this link too... http://www.autohobbydigest.com/8_75.html Bill M On Nov 16, 2007 9:32 AM, Derrick Brown <63max426@xxxxxxxxx> wrote: > hi all, > > center section questions. > ive got a completely rebuilt 489 cased suregrip (bearings , ring/ > pinion and suregrip) with new 3.55s in it. > > I want to swap to a steeper gear (likely 4.10, 3.91 minimum I think) > since im running a tall tire. > I still have my 742 case. > "IF" i want to get a new 4.10 ring/pinion for the 742 case ( i think > all ill need is a shim kit for the pinion gear). Will my large yoke > and all the new bearings , suregrip and carrier(from 489) all swap > over to the older style case? > It is my understanding that the only difference is the ring/pinion > with shims (742) versus ring/pinion crush collar (489) > > True or false, and what am I missing? > > thanks, > > > Derrick Brown > '63 Sport Fury, 4 speed > derrickb@xxxxxxx > > > >