[drewm]

Replacing my rear in my 66 GTO (late 66 style rear, according to measurements), and I am trying to figure out what years will bolt in? I am looking at a 1970 rear that is for sale on this site, but the spring perches are different and before I buy I want to make sure it will fit. I have googled and found very little info. Some places say anything from 72 and earlier will bolt in. Others say only 67 and earlier. Does anyone have any real experience in swapping in a newer rear into a 66? I know I could go custom ford 9", but I am working with a budget...(yes, funny, I know)

[steve25]

Do you not have a rear now?

[Formulajones]

68-72 rearends are wider. By 1 inch I believe. They physically bolt in but generally you need offset wheels to compensate. Skinny stock wheels and tires can usually still fit but look a little funky on 67 and earlier a bodies with a rear that's too wide.

[drewm]

Originally Posted by steve25

Do you not have a rear now?

I do, but recently found out the pinion gear is chipped up and unusable. Also noticed that one of the upper control arm ears is welded. When I bought the car, I figured that I was going to rebuild this rear, but with the busted up gear and mounting ear, thought it might be a better option to just get another complete rear that is in better, rebuildable condition.

[drewm]

Originally Posted by Formulajones

68-72 rearends are wider. By 1 inch I believe. They physically bolt in but generally you need offset wheels to compensate. Skinny stock wheels and tires can usually still fit but look a little funky on 67 and earlier a bodies with a rear that's too wide.

I think I've looked up every google match on pontiac 8.2 rears, and saw so much conflicting info that it is very confusing. One of the things that I recall reading is that only with the chevy 8.2 rears is the 68-72 rears different. I also read that in mid-model year 1966, the GTO's switched to a wider rear.

http://www.iegtoclub.com/Tech%20Lib/...tification.htm

[drewm]

Originally Posted by steve25

Do you not have a rear now?

If my housing was in good shape, I would just get a new ring and pinion and go with it. But at this point, I dont want to throw money at a potentially weakened housing. I have no idea when the ear repair was made or how solid it is. My thinking was to find a better housing with usable ring and pinion and rebuild the seals and bearings.

[The Champ]

I have a '64 GTO and have had 3 different rears in it. All three rear ends were the 1" wider rear of the later A bodies. I was still able to run 255/60/15's with all 3 rear ends using stock GM 15x7" rims with 4.25" backspacing.

The first 2 were 8.2" Pontiac 10 bolts. The current one is a '68 Chevy A body 12 bolt.

That '70 rear end will work fine in your car, as long as you have rims with proper backspacing.

[drewm]

Originally Posted by The Champ

I have a '64 GTO and have had 3 different rears in it. All three rear ends were the 1" wider rear of the later A bodies. I was still able to run 255/60/15's with all 3 rear ends using stock GM 15x7" rims with 4.25" backspacing.

The first 2 were 8.2" Pontiac 10 bolts. The current one is a '68 Chevy A body 12 bolt.

That '70 rear end will work fine in your car, as long as you have rims with proper backspacing.

No issues with the spring mounts being a different style? Mine now is like a bolt down style, I think the later rears are just a perch that has sort of an inner housing that the spring fits over. I could be wrong about that since I only have my rear to look at.

[GoGoat]

I have a 66 GTO with a 70 GTO rear housing. Using my stock Rally I wheels no issues. If technically 1" wider, thans only 1/2" per side. Good Luck

[66sprint6]

Originally Posted by drewm

No issues with the spring mounts being a different style? Mine now is like a bolt down style, I think the later rears are just a perch that has sort of an inner housing that the spring fits over. I could be wrong about that since I only have my rear to look at.

You will have to get new springs to suit the new rear end. You are correct in that the '66 has the little kidney shaped plates bolting the spring down on the rear end, but '67 and up they just sit on the perches.

[Kenth]

1966-72 Pontiac A-body uses the same rearend width.
1964-65 was 1" narrower overall width.
Only 1964-66 uses the bolted down springs.

For '66, the 10 bolt center casting was p/n 9783393.

For '67, the 10 bolt center casting was p/n 9783393 (no change). This casting was also used for the '67 Firebird rear end assembly, even though the axle tubes were different and the upper ears were not needed/used.

Chevy A-body was different, 1964-67 was the narrower style, 1968-72 was 1" wider width.

Also, NO need to replace the springs using a 1967 and later A-body rearend on 1966 and earlier.

1964-66 A-bodies uses rear springs with one tangential end and one pig tail end.
1967-72 A-bodies uses rear springs with pig tail on both ends and the upper end bolted to the frame.

FWIW

[steve25]

I would just get a new auburn posi unit and new gears .
The shop that you have do the gear and posi install should weld the axle tubes in better and while there at it rede the upper control repair if it looks like it needs it.

There’s no sense in shelling out money for a used posi rear and stuffing it with new parts if yours is still usable!
Any original 8.2” rear with what maybe a good posi will not be good for long anyway and then your almost back at square one anyway!

[drewm]

Originally Posted by steve25

I would just get a new auburn posi unit and new gears .
The shop that you have do the gear and posi install should weld the axle tubes in better and while there at it rede the upper control repair if it looks like it needs it.

There’s no sense in shelling out money for a used posi rear and stuffing it with new parts if yours is still usable!
Any original 8.2” rear with what maybe a good posi will not be good for long anyway and then your almost back at square one anyway!

I completely get where you are coming from, but my concern is what I can't see. Clearly the rear was thrashed. I don't know what kind of forces you need to exert on the diff to break an ear and chip teeth off the pinion, but Im concerned the axle tubes or the axles will have an issue. True, any used rear that I get could have unseen issues as well. I guess it is a leap of faith no matter which direction I go.

['ol Pinion head]

Originally Posted by drewm

I completely get where you are coming from, but my concern is what I can't see. Clearly the rear was thrashed. I don't know what kind of forces you need to exert on the diff to break an ear and chip teeth off the pinion, but Im concerned the axle tubes or the axles will have an issue. True, any used rear that I get could have unseen issues as well. I guess it is a leap of faith no matter which direction I go.

WHAT'S the PURPOSE BUILD of the car???

thats the first thing that I always ask when someone's considering a differential build or total r/e replacement?

Second, from hands on experience, the #1 cause for edges of teeth getting chipped of a ring or pinion gear is a loose pinion, the pinion no longer being properly located, but moving slightly too & fro in its carrier bearing bores upon coast & accel. Can not relay how many 8 or 9 tooth pinion gear sets that I've taken out, that the R&P blew up from light coast to full throttle acceleration.

3rd, In instances where there is a gob more Torque being abruptly loaded to a weak design center housing rear, than the rear was designed for, there can be pinion deflection. This becomes more evident with lot of torque & really low gear sets, i.e; 4.33, 4.56, 4.88's.

[64speed]

By the time you spend all this money tracking down and rebuilding an inferior 8.2 you can buy a 9 inch from quick performance for not much more. You’ll be surprised

[drewm]

Originally Posted by 'ol Pinion head

WHAT'S the PURPOSE BUILD of the car???

thats the first thing that I always ask when someone's considering a differential build or total r/e replacement?

Second, from hands on experience, the #1 cause for edges of teeth getting chipped of a ring or pinion gear is a loose pinion, the pinion no longer being properly located, but moving slightly too & fro in its carrier bearing bores upon coast & accel. Can not relay how many 8 or 9 tooth pinion gear sets that I've taken out, that the R&P blew up from light coast to full throttle acceleration.

3rd, In instances where there is a gob more Torque being abruptly loaded to a weak design center housing rear, than the rear was designed for, there can be pinion deflection. This becomes more evident with lot of torque & really low gear sets, i.e; 4.33, 4.56, 4.88's.

In my particular instance, I just want to build a nice cruiser. Stop light to stop light fun and melt the rear tires occasionally.

[drewm]

Originally Posted by 64speed

By the time you spend all this money tracking down and rebuilding an inferior 8.2 you can buy a 9 inch from quick performance for not much more. You’ll be surprised

I noticed that also. Seems sacrilegious to put a ford rear in a pontiac, but I cannot deny their strength compared to the 8.2. There is an 8.2 nodular rear for sale that I was considering due to the added strength over a standard 8.2, but I guess I have to figure out where my money would be best served.

[Scarebird]

Another option OPH may explain better than me is a 1971-72 Olds or Buick A 8.5"; superior to a 8.2 but cheaper than a 12 bolt and you get bolt in axles.

I have one in my 71 with a Detroit TruTrac.

IIRC you may need to mod the prop shaft.

[drewm]

Regarding the 9 inch from quick performance, the price is tempting, but there are also a lot of high torque pontiacs running around with old 8.2 rears.

[carcrazy]

Quite frankly I've never had much luck with the 8.2 when the horsepower gets around 400 and sticky tires are used. If you are just looking to drive around and not thrash it you can go back with another 8.2, BUT if you have ideas of getting a little aggressive, do yourself a favor and get an 8.5, 12 bolt or 9".....you'll be money ahead in the long run!