Rear end options/suggestions?

[black_taco]

Hello everyone,
I will be fixing up my 85 Grand Prix in a year or so and was thinking it is never too soon to start picking up parts and planning ahead for the build. I have a pro touring type build in mind powered by a crate TPI motor. The GP has the stock rearend in it and I would like to upgrade it to a factory posi setup. Are the rearends that came in the Monte SS, GN, and 442s ALL 8.5" posi units that would bolt right in? Is this the most popular rearend upgrade for non-posi G-Body cars? What is a fair price for an 84 442 rearend? Thanks in advance for any opinions or input whatsoever!

Oh, and not that I would be able to find one, but out of curiousity, did the 2+2 and the Hurst come with the same 8.5" rearend as above?

 

[Blake442]

The stock rear in 99% of G-body's are the 7.5", which are only worth their weight in scrap.

If you want to score a G-body 8.5", the only cars that had them were:
The '84 Hurst/Olds (not '83), '85-'87 442's, and all '84(?)-'87 Turbo Buicks (T-Type's, GN's)

An 8.5 carrier will not bolt into a 7.5 housing.

It is a popular upgrade, although they are starting to become pretty hard to find, and the people that have them know what they are worth, usually in the $750-$1000 range, depending on its condition.

Another popular way to go is either a 12-bolt, or a Ford 9 inch, both of which are available as bolt in units, made to fit G-body's.

 

[black_taco]

Hey thanks Blake. I guess the reareand I was wondering about is actually from an 85 not 84 as I had stated earlier. So this would make it an 8.5" for sure? Or was the 8.5" an OPTION on the years of 442s that you have listed? Thanks!

 

[Blake442]

The 8.5 was standard equiptment on the cars listed above.

If you're going to make big power, the rising prices of 8.5's are getting close to that of a nice 12-bolt unit you can buy from Moser. We put one in a Monte at the shop I work(ed) at, and I wanna say it was like $1600 or so complete, minus brakes. Might be worth it to go that route.

 

[itsnotanova]

Black Taco, Every once in awhile I see an ad for a 8.5. If you're lucky to find one it still won't be as strong as a 12bolt or 9inch. There's a few post on here about how to tell if you have the weak 7.5 or 8.5. Even if you have the 7.5, don't worry because it's still strong enough to handle 350-400hp as long as you treat it nice.

 

[black_taco]

Thanks for the input guys. All of the 8.5" rearends are posi right? Was the 8.5" even an OPTION for GPs?

 

[Blake442]

Posi-traction was just an option.

No Pontiacs or Chevy's ever received 8.5's... Just those select few Olds' and Buicks.

For street duty, a 7.5 should hold up fine. It's when you start throwing things like wide slicks, spools and high hp/tq motors at them that they don't stand a chance. On the street, you'd probably never get enough traction to do any considerable harm, and there's a lot of people that run them. Although I'm sure it's in the back of their mind that it's a weak link in the chain.

 

[mali540]

8.5 Rear

I was wondering if anyone is running a high horsepower big block, with a 8.5 rear.It has moser axles and eaton posi.Had no problems with a bored out 427 and drag radials.Changed to a 540 w/slicks and snapped the shaft in two. Just wanted to know how much success you guys had.