Understood about there being a bunch of different part numbers for SM420 input shafts, as well as some of those numbers noted above that have been superseded by newer numbers for the same parts.

I could not find any reference to the "2387442" number, but did find an additional number "3787254" that seems to have been used from '62-'67.

Quite a rabbit hole to go down to chase all that info down. What I did find and saved some snap shots for posting later if anyone is interested, is there are 2 different input shaft part numbers listed for SM420s of various years/series that had the added description of "(1 1/4" shaft dia.)" tacked on the ends of the part descriptions. Primarily noted in the Chevy books from Oct '62 and May '79. But it doesn't indicate what this "1-1/4" measurement applies to.

Is it the actual OA spline shaft diameter, or possibly the diameter associated with mating up to the main gear shaft and bearings? I couldn't tell and further checks to try and see if their was a clutch disc with a corresponding 1-1/4" spline shaft opening (instead of the more common 1-1/8" shaft) left me scratching my head too.

I am going to let anyone else interested take a stab at this.

Dan

~ Dan
1951 Chevy 3 window 3100
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