# Replacing 66 GTO rear end with corporate 8.5 inch



## Alan B (Nov 21, 2011)

I have a 66 3.7 posi rear end in my car and I need to go to more of a cruising gear. I'd like to have a 2.73 to 3.08. I could just get the new ratio gears, but I think I'd have to change the carrier as well. Is there a "corporate" 8.5 inch rear end that is a bolt in? I like the idea of a stronger diff, and it seems that I might be able to find a posi rear end with the ratio I want for not too much money. All suggestions greatly appreciated.
Thanks,
Alan


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## Alan B (Nov 21, 2011)

Nobody? Somebody must have done this swap. Even if we don't need the extra power handling, the flexibility on available gears and availability of low cost posis seems to make it worth considering. 

If not, does anyone have suggestions for where to find 3.08 gears for an 8.2 10 bolt? Am I correct that I can buy a new posi carrier for that ring and pinion and be ready to go (once the rear end is set up)?
Thanks,
Alan


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## ALKYGTO (Mar 29, 2010)

For the cash outlay for the rear + the hassle why not consider an OD tranny? Automatic you could do a 200R4 w/an adapter plate or do one of the Tremec trannys for a stick.


Any similar year GM A-body will have a rear that will physically fit in your chassis, prolly won't be a posi, but more than likely will have that cruiser gear you are looking for. That would be the cheapest route.


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## 05GTO (Oct 6, 2004)

Alan B said:


> I have a 66 3.7 posi rear end in my car


Is this the original 8.2 Pontiac or a Chevy 8.2?


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## jetstang (Nov 5, 2008)

The 8.5 won't work in the car, they have metric chassis, or just don't bolt up, I know they don't work or everyone would be doing it. The 66 rear is 5/8" narrower per side than later rears, so keep that one. I think the break for the 3 series carrier is 3.36 or 3.23, so that's the lowest you can go for gear. 3.73 posi is very desireable. Should be able to find a usable carrier and someones takeout 2.76 gear. I sold my 2.56 rearend for $100, though single spin.


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## pontiac (Mar 6, 2011)

8.2 pontiac rears all use the same carrier, just requires a gear change, plenty of those lower 2.73 around. not so much for 3.08.


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## 05GTO (Oct 6, 2004)

Someone correct me if I am wrong, but didn't pontiac offer the 3.55:1 and 3.90:1, Chevy used the 3:73:1.

:confused

You can purchase a ring and pinion from Randy's


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## geeteeohguy (Feb 2, 2008)

The 8.2 Pontiac rear does NOT use the same carrier. There are three different carriers: 2.56-2.78, 2.93--3.23, and 3.36-4.33. If you have a 3.73 ratio, it is indeed not a Pontiac ratio and you may have a Chevy rear end. Not sure about those. If a BOP ten bolt is what you have, you could "bolt in" a set of 3.36 gears and be set. If you want it more highway friendly, your best bet is a whole new rear end, bought used, on the cheap. The highway geared rears go for very little money, and can be found fairly easily and are a bolt-in deal. If you want a limited slip diff, the highway diffs with limited slip are out there. If you find an open rear, an LSD unit can be added. I swapped from a 3.36 open in my '67 GTO to a 2.56 posi (it was a freebee) and I love it.


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## Knuckledragger (Nov 25, 2011)

I have a 12 bolt 2.73 posi out of a 69 El Camino that will fit your car. It was in my 65 for many years and I just bought the posi carrier a couple of years ago which I rebuilt. PM me if interested.

Mike


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