GM Axle Posi Unit Interchageabilty

[72step]

My cousin has been wanting to swap in a oem type Posi unit into the rear of his 1972 Chevy C10 pickup, and I'll be helping. We've both heard different stories as to what interchanges. Some say it has to be from the same type of 67-72 Axle, others say certain GM carriers will interchange and fit all the way up to the 80's and early 90's as long as it's 12 Bolt. Does anyone have in info on this? If a posi unit will fit from the 73-87 it would be easier to find a donor from a junkard or something. What fits? What doesn't? Thanks.....

PS: I know on Chrysler Axles and Dana Spicer axles many of the carriers interchange from 1960's up to early 2k's on certain parts. I'd really just like to get the down low on GM carrier/axle parts interchageabilty. Many Thanks in Advance!

[cdowns]

car and truck 12bolts are different and not interchangable

[Mike C]

12 bolt truck cases will interchange. Most of the '73 and up are the "Gov-Lok" aka "Gov-Bomb" and not the Eaton like the earlier trucks. There are (2) series of positraction cases for 3.73 and down and for higher numeric ratios.

As noted, car cases are not interchangeable.

[72step]

Okay so we would want a posi unit from a 72 and older truck? How hard are these to find and how much can we get one for?

How far back in years are these available? Back into the 60's?

[Indyuke]

Check junkyards. The last one I got was from a '69 12 bolt. Yanked it out and payed $15 for the posi unit and ring gear. Unfortunately I didn't have time to pull the pinion.

[72step]

Originally Posted by Indyuke

Check junkyards. The last one I got was from a '69 12 bolt. Yanked it out and payed $15 for the posi unit and ring gear. Unfortunately I didn't have time to pull the pinion.

Thanks, so any 12 bolt 67-72 could have one huh?

Aren't the 60-66 axles similar?

[Indyuke]

I was under the impression that eaton posi units came in many different rears... and not just in GM either. But the one I pulled out came from a GM truck 12 bolt.

[Mike C]

Eaton was common to GM. I don't think until the more recent aftermarket posi's were Eaton's common in anything else.

I don't know who made Ford's traction lock, and most other manufacturers use Dana axles (I know there are exceptions...just generalizing) which were TracLock or PowerLock, which were both available in GM Dana 60's and possibly 44's in the '67 and earlier trucks or the front of some 4x4's.

Once again, only interchangeability is to like differential housing. 12t to 12t and they need to be the same gear series. 3.07-3.73 and 4.10 and up etc.