GN Rear question

[fodoimp]

what rear would come in an 84 grand national. Curious on gear size. Thinking about swapping one out for the rear that came in my 86 cutlass supreme 3.8L car. Do they hold up well or is it not even worth it?
I have a nice healthy v8 in the car now and the rear is the only thing holding this car back. thanks for the help

 

[R/T kota]

well assuming its the same diff they used in the 86 87 cars, it would be a 3.42 gear 8.5 diff. Not all were posi though. Believe it or not it was an option and not standard on the GN.
I've seen cars in the 8s with 8.5 diffs. Not stock mind you, but the parts are their to make it very strong.
A stock 8.5 will take alot of abuse before breaking.

 

[marcar1993]

No way, not worht anything, you should ship it to me. I'll take care of that peice.

jk, Definatly a good idea. It would be a 3.42 8.5. That is plenty strong enough for nearly anything in stock form as long as you don't run slicks.

 

[pontiacgp]

there was an optional gear....373...the RPO code for it was GT4

 

[85_SS]

GN's only had 3.42 rears. The 8.5 3.73 rears came in the 84 H/O and 85-87 442.

 

[pontiacgp]

according to G body.org

" First, ALL GM 1981 to 1988 G-Bodies used a 7.5" ring gear rear axle EXCEPT: Monte Carlo SS - 7-5/8" 3.73, Olds 442 - 8.5" 3.73, T-Type and Grand National - 8.5" 3.42 or 3.73. "

http://www.g-body.org/tnt/diffs/diff-codes.php

 

[R/T kota]

according to G body.org

" First, ALL GM 1981 to 1988 G-Bodies used a 7.5" ring gear rear axle EXCEPT: Monte Carlo SS - 7-5/8" 3.73, Olds 442 - 8.5" 3.73, T-Type and Grand National - 8.5" 3.42 or 3.73. "

http://www.g-body.org/tnt/diffs/diff-codes.php

Never seen a turbo regal with a 3.73 in it from the factory.
Have to check the TR forums to confirm this.

 

[85_SS]

I could be wrong, but I would almost guarentee there is some inaccurate info on that site:

according to G body.org

" First, ALL GM 1981 to 1988 G-Bodies used a 7.5" ring gear rear axle EXCEPT: Monte Carlo SS - 7-5/8" 3.73, Olds 442 - 8.5" 3.73, T-Type and Grand National - 8.5" 3.42 or 3.73. "

http://www.g-body.org/tnt/diffs/diff-codes.php

It's definitely partially inaccurate with regards to the Monte SS because 83/84 SS's had a 7.5" rear. They also left out the Buick Turbo-T (8.5" 3.42) as well as the 84 H/O which had the 8.5 with a 3.73 rear.

One thing I am not 100% sure on, is I believe ALL g-bodies went to a 7.625" rear in 1985 (in place of the 7.5"). I'm also not sure if the 307 V8 T-types came with an 8.5" rear or not.

I'm not sure why the author can't tell the difference between the two rears - the "fangs" on the bottom of the rearend area dead giveaway:
http://dyeager535.topcities.com/diffid.html

 

[pontiacgp]

weren't all T types the 3.8 turbo?..

 

[R/T kota]

weren't all T types the 3.8 turbo?..

Nope
The 3.8 turbo was standard only on the GN/GNX but was an option on the T types.

And here in Canada most of the v8 cars were 305 chevys not 307 olds like in the U.S.