Which POSI wil fit my 69 C10 3 series Differential
 

I have a 69 C10 with the factory 3:07 Ring Gear and Pinion in it. I is my understanding because I have the factory 3:07 it means means I have a 3 series case.
I am going to upgrade to a 3:78. I have purchased a 3:78 R & P from Summit which will fit my 3 series case.
I have now decided I would like to add a POSI. In looking at Summit and Jeggs I seem to get conflicting info as to whether a POSI is available for the 3 series case.
Does anyone have any thoughts on a POSI that would fit 3 series case with the 3:78 gear?
Also, is any modification required to the diff to make the POSI fit?.
Thanks

Re: Which POSI wil fit my 69 C10 3 series Differential
 

The Posi IS the case...

Yes, the 3.07 have a 3 series case. The 3.73 (right?) are normally in a 4 series case, but you can buy a thick gear as it looks like you have done. Now you just need to buy a 3 series positraction to fit your gear.

I would by the Eaton or the Yukon DuraGrip. I prefer those over the Auburn unless you can still get a Pro with clutches.

Re: Which POSI wil fit my 69 C10 3 series Differential
 

Drive Train Specialists has the 'case' you need:

http://www.drivetrainspecialists.com...ed19587-1.html

This is an Eaton series 3 carrier for an 8.875 in truck 12 bolt diff.

Re: Which POSI wil fit my 69 C10 3 series Differential
 

Yukon duragrip isn't available for a 12 bolt truck application. All the research I've done suggests new Eaton or pull one from a junkyard and then have it rebuilt.

Re: Which POSI wil fit my 69 C10 3 series Differential
 

Huh. Funny, I'd looked all through their applications but never noticed that. I'm planning on one for the 9.5" in my Jimmy. And maybe my 11.5" instead of the Gov-Bomb.

Goes to show you even the aftermarket doesn't want to support the truck 12 bolt.