GM Posi Units

[getchasum]

What all cars, trucks, etc would have a pos unit that I could swap into my open unit?

Time to go juck yard diving.........:biggrin:

 

[turbofish38]

Most 88 and older B-body(Caprice,LeSabre,Park Ave,Olds 88/98,Bonneville,Parisienne) are your best choices. 1989 and newer wont work. Those are 30 splines and you want the 88 and older 28 spline. Stay away from the trucks. They use the weak gov-lock unit. 81 and older F-X body will also work but those are imposssible to find.

 

[ijames]

Eric, so does that mean if you want to step up to 30 spline axles an 1989 or newer B body would work? Now you tell me, after I paid for an Eaton (3 years ago ).

 

[getchasum]

Most 88 and older B-body(Caprice,LeSabre,Park Ave,Olds 88/98,Bonneville,Parisienne) are your best choices. 1989 and newer wont work. Those are 30 splines and you want the 88 and older 28 spline. Stay away from the trucks. They use the weak gov-lock unit. 81 and older F-X body will also work but those are imposssible to find.

Eric, did GM code them G80 as well or what code do I need to look for on the truck lable? Most of the stuff around here is almost buried to the axles and getting help is a joke.

 

[ijames]

So far as I know GM always uses G80 for limited slip. What's actually in the rear depends on the vehicle. Regals got the eaton-style posi's, truck got the gov-lock, but both build sheets say G80.

 

[turbofish38]

Yep, G80 on all posi's. Even the 30 spline truck units are the weak gov-locks. Just say no to trucks. Lots of 91-96 Caprice cop cars in the bone yard if you need a 30 spline unit and those came with the Auburn unit. Just like what is picture in the Jegs catalog. And most of the 91-93 cop cars had the 3.42 ratio to boot.

 

[Red Regal T]

Don't forget 2nd gen Z-28s and Trans-Ams. Most, if not all have the correct posi-unit. You may or may not need a ring gear ratio depending on the donor's gear ratio.

 

[turbofish38]

The big thing one must relize when you're looking at boneyard parts is the fact that they are also out of 20-30 year old cars and may be in worst shape than your broken pieces or just plain worn out and not rebuildable too. Shop wisely. The 8.5 as we know it goes all the way back to 1970. It was pretty much standard issue on everything built back to 1972. Novas,Chevelles,Camarobirds all used them. I dont see to many posi's out side the snow belt states.

 

[turbobuick1]

Quick question Eric, does it matter if the donor vehicle has a 3.42 gear ratio or not? I'm looking to go junkyard diving tomorrow, and would love to find a cheap way to put a Posi in my open rear Buick. Is there anyway to cross reference a GM part number for an 87 GN limited slip carrier with another car?

 

[turbobuick1]

And it has to be an 8.5" correct? Appreciate any expertise I can get on this.

 

[mikestertwo]

And it has to be an 8.5" correct? Appreciate any expertise I can get on this.

It has to be an 8.5" series 3 carrier. My memory is fading but if I remember correctly the older series 3 carriers had an "8" cast into the side of the carrier. If it is a series "2" it will have a "9" cast into the side of it which you can't use with 3.42 gears unless you use a spacer on the ring gear. I think any ratio 2.73 and above is a series 3 but it's been a while so I could be wrong.

 

[turbobuick1]

Good stuff! This was something I was unaware of. I'll have to dig up some more research on this. Any other input on this is welcome!

 

[GNeric]

Correct. The "3 series" is a 2.73 and up carrier. Not sure about the numbers "8" and "9" as I really should have paid attention when I had some handy. :smile:

It has to be an 8.5" series 3 carrier. My memory is fading but if I remember correctly the older series 3 carriers had an "8" cast into the side of the carrier. If it is a series "2" it will have a "9" cast into the side of it which you can't use with 3.42 gears unless you use a spacer on the ring gear. I think any ratio 2.73 and above is a series 3 but it's been a while so I could be wrong.

 

[mikestertwo]

Correct. The "3 series" is a 2.73 and up carrier. Not sure about the numbers "8" and "9" as I really should have paid attention when I had some handy. :smile:

I have one of each sitting in my shop

 

[GNeric]

That helps. I never wrote anything down out of all the units I have had over the years. Lately I have been writing things down so I don't have to rely on my "brain power" for trying to help someone out.