Can anyone tell me what this is

[SoFloG]

How would you determine if it was done well or not? Just by how it functions/rides?

Axle tubes shortened, trailing arm mounts added or relocated, and leaf spring perches removed. There may be more to it but these are the basic mods that might be visible on an 8.5 out of a pickup or fullsize car, that was converted to fit in a Gbody.

 

[69hurstolds]

It's all painted, so it may be hard to read, but the front of the axle tube on passenger side will have a stamped code on it. Once deciphered, that code tells you exactly where the rear end came from and what ratio it left the factory with and whether it was a posi or not.

G-body 8.5" posi axles are like hen's teeth in a way because G80 (limited-slip) was not part of any dealership ordering package. If the dealer did not specifically order G80 as an a la carte option, it didn't come with limited-slip. This is why most dealer floor plan models were ordered without G80. Conveniently during the years the 8.5 was availabe in the G-bodies, the dealers had a quicker process called "select-a-unit" where they just popped down a code which included a boat load of "packaged" options. Different codes included different levels. There were a few savvy salesmen that knew what to do and ordered G80 for their lot cars, but that was fewer than one would think. GNX I think was the only car that came with posi standard but that was just a handful of cars.

And usually, if they were qualified options, you got the WL7 RPO added to the order to provide a package discount. The WL7 was not automatic. If the dealer didn't write that down with the qualifying RPOs, the discount was not applied.

 

[DRIVEN]

How would you determine if it was done well or not? Just by how it functions/rides?

You didn't give much to go by in your first post other than the one photo. If it's still installed in a Gbody and the wheels don't have some funky offset, it's most likely a factory Gbody 8.5. It either firs or it doesn't.
If its out and in the corner of the garage, you'll need to be more ctitical. Other guys have already mentioned things like ground off leaf spring perches and shortened tubes. The stamped code is the surest way to DNA test it. If it looks legit and you're ready to hand over the cash, I'd ask the seller if you can pop the cover off and look inside. Then you'll be able to verify the ratio and see if it's posi or open.

 

[Ribbedroof]

The center casting was unique to G bodies, because of the upper ears. B bodies also used upper ears, but at a different angle and location.

B body/earlier A body rears installed in a G body require modifications to the mounting system for the upper arms. Done well would use arms with a roto joint to accomodate the differences, and I beleive I have read of one installation with cut/welded upper arms.

Leaf spring/trucks didn't use mounting ears, so pretty unlikely it's one of those. Some (70-72) earlier A bodies used a few, they are wider than the G body unit. The "big" A bodies (73-77) also used them, and are even wider as I recall.

Might ask/look for the center section casting number (usually located at the front lower edge of the case), and check against known G body applications.

Like I said before, slim chance, but for the price legit g body 8.5s are bringing, I'd want to be sure what I was buying, But that's just me.

 

[ssn696]

The Caprice/B-body 8.5" differentials have the upper control arm bushing mounts in a lower, wider, more forward position than the G-body version used in the GN and 442, which exactly duplicate the location on the smaller more common 7.5". Compare with your axle before taking home the one in the picture.

The simpler check is the width. A G 8.5 is about 58" hub to hub while the B version is wider. Finally, the B-bodies usually came with a 5x5 lug pattern. Modifying a B axle to fit a G is quite an involved process.

 

[pagrunt]

Some (70-72) earlier A bodies used a few

It'll be cars built from Jan '72 that started using the 8.5" to replace the Chevy & BOP 10 bolts. My '72 Monte was a late year car that had it.

 

[Clone TIE Pilot]

With the Caprice 8.5 rear axles they had two different wheel bolt patterns. Normal Caprices had 4.75x5 wheel bolt pattern while the police package 9C1s had 5x5 truck wheel patten.

 

[Longroof79]

With the Caprice 8.5 rear axles they had two different wheel bolt patterns. Normal Caprices had 4.75x5 wheel bolt pattern while the police package 9C1s had 5x5 truck wheel patten.

I believe B-body wagons also used the corporate 5 x 5 bolt pattern.

 

[86LK]

Category:Rearend

www.crankshaftcoalition.com

this site used to have great info. looks like some scumbags took it over

 

[CopperNick]

Could try taking a good hard look at the various tabs and the upper and lower control arm hanger brackets that are welded to the tubes. The factory welds tend to have fairly clean and finished appearances. If the tabs look as if they were cut away from a donor rear end and grafted on to that one then the welds might look professional or could also look like blobs of bubblegum. That pretty black paint job could be camouflage to hide work that had been done to adapt the assembly as has been suggested above.


Nick