65-76 posi diff parts
 

There's been some chat lately on facebook groups about how some Chevy 12 bolt differential parts will work in the 65-76 B body posi diff, namely the clutch packs for certain. Less certain is the spider gear thrust washers and cross shaft, which may imply spider gears as well. These are all the usually worn out items. Axle side gears are definitely excluded, as Pontiac is 31 spline, Chevy 12 bolt is 30.

It is my understanding the 65-67(or 65-70?) posi diff uses a weaker .750" diameter spider shaft. 71-76 diff use a stronger .875" shaft and corresponding larger spider gears. Can anyone verify the correct date ranges and sizes? As for 12 bolt Chevy, they have a .808" diameter shaft. I have a few mid to late 60 B Pontiac open diffs that have .808" shaft as well, so maybe that is possibility for interchange?

Lastly, is there a source for new .875" shaft and thrust washers, and maybe even spider gears?

Paging ol' pinion head...anyone know him?

Arowhed, Hello!
Regret, next to never get on here anymore. Too many projects, and life is too short. unfortunately this board is not the quality resource it was for many years.

On your diff question, other than stumbling onto correct application NOS side gears & spiders, there is no source for new side gears & spiders.
In the late 80's & up into the early 00's, . when i was on the road a ton & cleaning out PickNPulls & crusheryards w my specialty core program, I'd watch for & pull the mid & low ratio 28 spline MP series posi carriers. Then would pull the 31 spline side gears, spiders, plates & springs, etc out of the '71-74ish Pontiac P series posis. Properly shimmed up. then would assemble a mid ratio or low ratio posi carrier in that later case for usage in a '65-70 P series big car rear. Those early 80's low ratio (3.42) MP series posis have been quite hard to find over last 2 decades. The mid ratio MP series carrier (usually w 3.08's or 3.23's) is a more common find, & then when rebuilt w 31 spline side gears & spiders, can be properly assembled with a 12bolt chevy ring gear spacere in a 3.42-3.55-3.73 geared 65-70 P series rear. Hope this helps, when am out in the shop will watch for a high ratio '71- P series posi case & note the EDB number.

Ol Pinion Head: Really miss your posts on this forum. Always learn new things, always accurate, always appreciated. I know life and projects can keep us really busy but not many people left alive have the vast body of knowledge you can share. The forum may be suffering a bit because you have been absent. Hope you can post again when time allows.

The clutch packs are a multi-application GM part that fit several differentials.