Which rear to use on a Pro touring G body??

[85GPLEf41]

Well...I am beginning to start my 85 GP's build and i am questioning which rear diff to use for a G body Pro-touring ride.... There are 3 choices:
1. 87 Monte SS 3.73's 7.5 10 bolt with a Zexel Torsen from a newer Camaro SS and some GN used axle's with a Summit rear diff girdle..
2. 85 442 rear with 3.42:1 open diff..
3. 87 GN with a posi and 3.73 gears.
I planned on getting a 8.5 girdle and a Truetrac lsd unit but what would benefit me the most??The 8.5 Truetrac diff is $$ along with the girdle.... what would be my best choice??

[Tony_SS]

If you aren't drag racing, I think the factory 7.5 with an Eaton or Auburn unit and girdle are plenty strong IMO. The 8.5 is nice, but not at what they are going for now, unless you are running sticky tires and drag racing.. I'd wouldn't go out of my way for an 8.5

[85GPLEf41]

I already have the differentials... I got both 8.5's at real good prices last year, the 442 one was from a totally smashed car. The GN one was pulled from a drag racing Monte at the junkyard along with Hotchkis rear upper and lower control arms and braces which i also pulled.. The 7.5 diff wasgoing to be used and i was collecting parts to build it up till these came along. I really don't want to spend anymore money on the 7.5 unless if it would benefit me more then the 8.5's. If i use the 8.5's should i buy a Truetrac or keep the original GN posi? I will buy the girdle and rebuild it before using it.

[Hotchkis]

I already have the differentials... I got both 8.5's at real good prices last year, the 442 one was from a totally smashed car. The GN one was pulled from a drag racing Monte at the junkyard along with Hotchkis rear upper and lower control arms and braces which i also pulled.. The 7.5 diff wasgoing to be used and i was collecting parts to build it up till these came along. I really don't want to spend anymore money on the 7.5 unless if it would benefit me more then the 8.5's. If i use the 8.5's should i buy a Truetrac or keep the original GN posi? I will buy the girdle and rebuild it before using it.

Ernesto – That’s a good find in a wrecking yard! Congratulations!

[85GPLEf41]

Thanks! best part was that i paid $160 for the rear, the upper and lower control arms,braces, and rear sway bar were thrown in for free!! Believe me i was HAPPY to find this score! It happened after pulling the 442 rear on the side of the street in a business complex..in less then 45 mins... I plan on cleaning up the rear and arms and using them in a future g body build....What rear would you guys use to build a g body platform? I know the 8.5 is the probably the best to use but which posi? I've read a open posi is better then a "drag" racing posi. I plan on doing some frame mods ie: frame notching, bracing etc etc.. but obviously it won't be like Holley's GP build but i hope i can closely follow it when $$ allows... BTW would the non-swivel/adjustable Hotchkis arms/braces be OK for a Pro-touring build?
Thanks!

[Tony_SS]

I would think an Eaton or Auburn or even a factory clutch style posi would be fine... you don't wan't a locker or anything like that.

I run tubular upper and lower CA's from UMI with a 1" sway bar. There are some nice arms that have those swivel bushings and I think those are desired over the standard poly ones..

[Scott Parkhurst]

A TrueTrac diff would be ideal in an 8.5, and control arms with Johnny Joints will allow more travel and don't bind. But what you've got is a lot better than the factory stuff.

[Hotchkis]

Ernesto – That’s a screamin’ deal! Those arms should be great for your Pro-Touring build. Your Hotchkis arms are much stronger and with less pliable bushings than stock. For the price, it’s a win-win for you!

[BulldawgMusclecars]

I'd run the GN rear. I had more than enough of 7.5 "Vega rearends" when I was working on mostly 3rd and 4th gen F-bodies.

[Nothingface5384]

gn rear is stronger, and you can upgrade it to 30 spline axles
check out jdrace for parts

if there was a way to fit a 71-72 skylark/gs/cutlass 8.5 rear then you;d be gaing bolt in axles and bigger axle tubes...3in vs 2.5/8(g-body/s10)

[UNGN]

What rear axle really depends on what motor/Transmission you are using. I would swap the 3.42 gears onto the Posi 8.5" and sell the rest to buy a set of 28 spline forged axles.

[85GPLEf41]

Ernesto – That’s a screamin’ deal! Those arms should be great for your Pro-Touring build. Your Hotchkis arms are much stronger and with less pliable bushings than stock. For the price, it’s a win-win for you!

Especially when being on a budget:( So the GN rear sounds like what i will be using. I thought i read somewhere that a open diff is better for handling then a drag racing posi.. I am hoping to build up the 442 rear end later with a truetrac and 30 spline axles but that's later on in the future.. As for the engine and trans combo i will be swapping in a 98 Firebird Formula LS1 and a "built" 4l60e with a list of upgrades that the builder said should be better then the regular 4l60E. It has a stall converter but don't remember the stall but he said it's what a Corvette would have.