# Rear end track



## Eric Animal (Oct 28, 2007)

What year was the GTO's rear end width increased? I always forget. I have a 67 GTO, and a 1958 brain :willy: thanks, Eric


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## geeteeohguy (Feb 2, 2008)

Eric, it was increased by one inch in 1966. Otherwise, the same rear end as a '65. You can do a quick check by looking at where the shock mount is welded to the carrier tube: on a '64 and '65, you can only fit one finger between the mount and the backing plate, and on a '66 and up, two tingers, just like that old brand of tequlia! The advantage of a '65 rear end is that you can fit a little wider tire back there. Other than that, they're the same and it's a bolt in deal. Have fun!!!


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## wingnutooa (Feb 4, 2009)

not sure if this is concrete or not but it makes sense in my head.

the 1 inch narrower axle means shorter axle shafts. less likely to twist bend or break!!!!


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## Too Many Projects (Nov 15, 2008)

geeteeohguy said:


> Eric, it was increased by one inch in 1966. Otherwise, the same rear end as a '65. You can do a quick check by looking at where the shock mount is welded to the carrier tube: on a '64 and '65, you can only fit one finger between the mount and the backing plate, and on a '66 and up, two tingers, just like that old brand of tequlia! The advantage of a '65 rear end is that you can fit a little wider tire back there. Other than that, they're the same and it's a bolt in deal. Have fun!!!


On the Chevelle line the rears got wider AFTER 67....68 and up. So if I were to put a 67 Chevelle 12 bolt under my 67 GTO, what are the differences ? Didn't Pontiac use a Chev axle when a 12 bolt was ordered ?


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## Eric Animal (Oct 28, 2007)

Thanks Jeff. And an interesting point Wingnut. I have a stock 400 w/a th400 trans. i don't think i will be snapping any axlesarty: TMP, I am not sure if a Chevy 12 bolt rear was used in a GTO....maybe Olds or Buick..i am told that a Buick rear is very strong. Years ago i had a 12 bolt Chevy rear in one of my 66 GTOs...went right in and took a heck of a beating! Eric


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## geeteeohguy (Feb 2, 2008)

Thanks, guys. TMP, from what I know, the 12 bolt was used in the 455 GTO's starting in 1970. It was a BOP rear end, not a Chevy. I believe the Chevy uses C-clips to hold the axles in, and the BOP rear end does not. Any Chevelle 12 bolt will happily bolt right in to your GTO with no mods or problems. Of note, there's an article in "The Big Little GTO Book" about rear ends: it seems that Buick, Olds, and Pontiac got the best gears and components, and the "seconds" went to the Chevrolet plant for use. Gotta remember, Chevy was the bottom end of the GM line!!


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## dannla (Aug 31, 2008)

The rear axle witdth was increased by one inch in 1967. The 64-66 are the same and the 67-72 are the same (width wise). The 12 bolt was introduced to the Pontiac A-body lineup in 1970. It came as standard equiptment with the 455 engine and was not available from the factory with other engines. The 12 bolt that was used is the BOP style without c-clips. 

:cheers


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## geeteeohguy (Feb 2, 2008)

In my experience, I have found the '64 and '65 to be 1 inch narrower, and the '66 and up to be an inch wider. This is for the 10 bolt rear end.


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## LTGOAT (Oct 19, 2009)

*67 gto rear axle swap*

Hey guy's 
I need help on an axle swap (it's bent) it is a 10 bolt 3:55 do these axles have clips at the carrier so I can remove it (the bent axle) without removing the whole rearend.



Thanks


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## Eric Animal (Oct 28, 2007)

A Pontiac 10 bolt axle is held in place at the flange where the brake mounting plate is attached. Remove 4 bolts and the axle SHOULD pull out. No c-clips.


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## 05GTO (Oct 6, 2004)

Eric Animal said:


> A Pontiac 10 bolt axle is held in place at the flange where the brake mounting plate is attached. Remove 4 bolts and the axle SHOULD pull out. No c-clips.


:agree



LTGOAT said:


> Hey guy's
> I need help on an axle swap (it's bent) it is a 10 bolt 3:55 do these axles have clips at the carrier so I can remove it (the bent axle) without removing the whole rearend.
> 
> 
> ...



If you've ever considered rear disc brakes, now would be a good time to do that conversion.

P.S. Welcome to the forum,


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## PontiacDave (Jun 9, 2009)

The 10 bolt Pontiac definitely got wider in 1967......but I always thought that all 12 bolt A-body differentials were the "C" clip style? I do know that the 10 or 12 bolt terminology refers to the # of bolts holding the ring gear to the carrier. It just so happens that MOST of the time it is the same # of bolts holding the inspection cover to the diff. The Olds has a 12 bolt diff that has a 12 bolt "inspection" cover but has only 10 bolts holding the ring gear on to the carrier. It is considered pretty weak compared to a true 12 bolt. I have never seen a true 12 bolt without "C" clips......but hey, I am far from a true expert, and have been wrong a lot before.....just ask my wife :lol:


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## pbearly (Apr 18, 2013)

So I just got done reading this post and on my 64 I have 256 gear posi that I want to swap for a lower gear. I found an entire new axle for the car with 390 and a posi, all parts are new. The problem is that the axle is 1 inch wider so it must be the newer axle. I also noticed that the newer axle appears to be stronger with more webbing on the center section. Any issues with me installing this on my 64? I know I may have a tire issue, they currently don't rub but 1/2 inch is a big change.


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## 68greengoat (Sep 15, 2005)

pbearly, this thread is 4 years old. It's best to start your own thread rather than dig up and latch on to old threads..... pbearly is better than not p'ing at all.......


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## Too Many Projects (Nov 15, 2008)

The width may necessitate a different wheel offset to clear the fender but my first concern is that a '64 axle had a smaller bushing for the upper control arm. I'm not certain if the control arm is compatable with a newer axle but you can get a newer control arm to change over, just more parts and money.

Might want to do more research to see what is involved with that.


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## geeteeohguy (Feb 2, 2008)

The '64 housing upper bushings are smaller in diameter than the '65-up housings, but the center of the bushing and location is the same. The '64 arms will bolt right up to a later housing. No real issues using the later rear end except for a hair less wheel/tire clearance. You may need more backspace on the rear rims. As a side note, don't toss the 2.56 posi: 3.90 gears are terrible on a street driven car. BTDT, and cruising at 50 mph is no fun at all, and paying the increased fuel bills is a bummer. A better compromise gear that does it all would be a 3.23. I swapped the 3.36 rear on my '67 GTO for a 2.56 posi, and I love driving the 2.56: great mpg at high speeds, and the car is a joy to take on road trips now.


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