Pinion Gear Splines Update

1970 Challenger TA with 3:91 Gears.
Which is correct for a 489 case pinion spline. A 10 spline pinion or 29 spline pinion. Did 1970 use both splines. Which application for which car.
Something not adding up. Ring Gear # 2070225 3.91-1 MS291 8-4-69
Pinion # 2881460 3.91 3-6-69 10 Spline 7290 Yoke

Both are available, depending on ratios, manufactures and luck.

Agreed, but I've found the 10 spline more uncommon on E body 8 3/4 chucks over the decades

Yep, there doesn’t seem to be a formula for determining which is “correct”.

The Parts book shows both 10 and 29. with notes on each. Looks like 70 - 71 may have had a running change at some point

now for the related question, are the 10 and 29 spline yokes the same for all the 8 3/4 housings [741, 742, 489] that use whichever spline count ?

Off Topic but is it common for the dates on the ring and pinion to be that far apart?

That's what I am asking. I though the ring & pinion where matched sets made together.

The dates are made into the parts at the time of manufacturing. Ring and pinions are then put together in a machine and lapped as a set.

You'll probably never see a set that have both matching dates the same on the ring and the pinion.

Tom

Ok Thanks, That clears that up.