I have searched page after page and one thread says one thing an another says something??? What is this rear end so I can get a posi unit and gears!

 

Read this page.

It looks like a corporate 8.5 housing to me. Gears and posi's a plenty.

http://www.buickperformanceclub.com/85rear.htm

 

Whats with the funky looking notched cover? Would a round aftermarket fit or is it is what it is?

 

Not uncommon to see a cover from an earlier built 8.2" diff end up on the later built 8.5" diff. Never judge a book or a diff by the cover.

 

Is that the only cover that fits, and this is a easy to find parts for 8.5? Thanks

 

The rearend assemblies were built by different divisions of GM. Yours is the same as my 71Cutlass. You will find a B on your passenger side axle tube along with the date and axle code. That cover it is for a Buick built assembly. That's why they are known as the corporate rear end, the easiest to get parts for. That design actually started in 71. My Cutlass has the Buick bult one and my 71 442 has the unnotched Olds built unit.

 

So that cover has to stay with that rear end and its also the 28 spline axles?
I was just wondering about the cover because if its off changing gears and unit I could replace it with either one of those fancy aluminum race ones or just a plain chrome one.

 

8.5 AND 8.2 bop do not SHARE THE SAME BOLT PATTERN ION THE COVER THEY MAY look THE SAME but they are not INTERCHANGEABLE

 

How come they don't make a 3:55 gear in between the 3:42s and 3:73s for the 8.5?
Im really leaning towards the 3:42s, I have 245/60/15s.

 

Not sure. They did for the chevy 12 bolt, but not anything else GM that I can think of off the top of my head.

 

Because the 3.55 would only be a 4% difference from the 3.42. Not enough to warrant the effort.

 

My brother-in-law's 68 GTO has a 3.55. It's one of those cone style posi, split carrier 8.2" 10 bolt rears.

This site shows 3.55 ratios were used in the Olds 8.2" rears as well:
http://www.oldsmobility.com/old/reardiffs.htm

 

Olds never had a rear in 1966 it was a pontiac rear or Buick rear. Only way back in 1964 65 was there a OLDS 8.2 which the GTO used as its rear too Pontiac and olds have shared rearsa for years. even 12 bolt olds have been installed in GTO rear in 68 69 60 from the factory
different plants where cars shared the lines have had this happen all the time.

1970 strike had Pontiac rears innto chevys (Monte Carlo and El Caminos) it was crazy...

 

Yeah, I should have said "8.2 rears used in Olds cars" instead of 8.2" Olds rears.

 

Please correct me if I am wrong but are you saying that the Type O 12 bolt that was used by Oldsmobile at all US assembly plants in 1968-1970 were also installed into some same model year Pontiac GTOs? I have never heard of this before.

 

Been offered a Chevy 12 bolt with a posi and 373s, probably take this deal.