Verifying a Posi Differential unit?
 

I’m starting a search for a Posi Differential for my 70 C-10 (I’m currently running the original “One Wheeler” with 3:73 gears)
While I’m at it with the upgrade, I plan on installing a more Highway friendly Ring and pinion gear set.
Other than happening upon a unicorn truck, sitting in a yard with the Posi Rear option showing on the SPID,
How do I verify that I’m getting an actual Posi unit?
Are there casting numbers on the rotating assembly,
or are there numbers stamped on it?
In either case, where would these numbers be?
I know these are a lot of questions but I just don’t want to get “took” out of ignorance.
I’m hoping someone would have a picture of a Posi rear end with the cover off to show the gears.
Thanks in advance

Re: Verifying a Posi Differential unit?
 

Here are some photos of an original factory Eaton posi unit and a new Eaton unit (19556-010). Both of these are series 4 size carriers for use with standard thickness 3.73 or 4.10 gears. If you want to go with 3.07 or 3.42 gears, then you will need a series 3 size carrier.

The posi carrier has the easy-to-spot springs and plates in the center of the carrier, whereas an open carrier will not. I'm not sure about the casting numbers for original units, but here is a new Eaton series 3 carrier:

https://www.summitracing.com/parts/etn-19587-010

Edit - It appears that the casting number for a factory series 3 posi carrier was 32212.

https://www.stevesnovasite.com/threa...ential.411706/

Re: Verifying a Posi Differential unit?
 

without looking at the diff itself, spin the PS wheel/drum forward. If DS also spins forward, its a Posi. If it spins backwards its peg leg

You can count how many times the pinon rotates when you turn the PS wheel. 1 revolution. Just over 3 turns would be 3:08. 3 3/4 turns, 3:73, etc for a posi rear end.

Re: Verifying a Posi Differential unit?
 

Thank you for your information.
This is exactly what I was asking for.
I found a “Complete Unit” with 3.42 Ring and Pinion on Amazon.
It’s from Yukon, and has good reviews.
I figure by the time I find an original unit, rebuild it, and buy the new gear set, I may be further ahead going with the new.

Re: Verifying a Posi Differential unit?
 

Here's a Video about the Recommend oil for that set-up.

Re: Verifying a Posi Differential unit?
 

I did this test on mine and thought it was one legged. When I pulled the cover a bunch of friction plates from the posi fell out. A rare occurrence but it can happen. Pulling the cover is best if possible.

Re: Verifying a Posi Differential unit?
 

yeah looking inside is best. the spin the axle thing is a quick way to see if it is a posi if there is just a bunch of rear ends pulled from trucks at junkyard.

Re: Verifying a Posi Differential unit?
 

I paid about $350 for a diff shop to pull the 1968 posi unit out from a T-Boned 3.73 rear end and rebuild it.
I intended to put it in my rebuilt 3.73 rear differential after the 500 mile break-in run, but now I find my propshaft also got bent in the collision, so I have to get that squared away, first.

Re: Verifying a Posi Differential unit?
 

This was gong to be my recommendation and I see you figured it out already. I'm doing the same thing with my Dana 60. New gears, Posi unit and rebuilt kit. A little more than what you found but it's OK.

Re: Verifying a Posi Differential unit?
 

If you go directly thru Quickperformances website, it is cheaper than they have it listed on amazon. I paid $525 for the kit and it came with a Yukon Dura Grip LSD, the gears did not have a brand on them though, just came in a red box.

https://www.quickperformance.com/GM-...e_p_20373.html