# Rear End Identification - Any Experts?



## goatsnvairs (Sep 12, 2014)

I am restoring a 1967 GTO and have started at upgrading the rear end. I knew it was an open rear. This weekend I looked into the ratio. Couldn't read the stampings so I counted the teeth, 41/15 or 2.73. Referring to Zazarrine's book I noted 2.73 was not a valid ratio for '67. I originally thought I had an 8.2 BOP 10 bolt, but now based on what I've seen I'm thinking 8.5 GM Corporate. It does have the scalloped cover, but I noticed the rear brake line mount is wrong, the case is tapped on top instead of the bracket that's supposed to come off the top cover bolt. Also noted a big "A" stamp in several places, a sideways "N", and a date code that looks like "924". First character hard to read. Have not found any numbers stamped into the axle tubes yet. Was hoping someone could help me ID this thing.


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## Pinion head (Jan 3, 2015)

The rear is the most common of the 3 different versions of the '71-72 8.5 A-body, have built well over 300 as posi rears off that particular style housing. The 8.5 A-body rear has a nodular housing and due to the way it was cast, has more pinion support than any 10 bolt or garden variety 12 bolt. With stock axles in an auto 3500-3700 lb A body, many many have been raced weekend after weekend into mid 11's on slicks. For considerably more strength, have upgraded quite a few A9 & A10 axle bearing versions with new 30 spline Eaton carriers & new custom axles.

Fwiw, in the early to mid 90's , I always ground the big A off these, as well as several other casting numbers. Also reshaped the big square lugs on the bottom to mimic those of an 8.2.


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## azmusclecar (Sep 26, 2007)

GTO Axle Identification


http://www.wallaceracing.com/axledata2.htm


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## goatsnvairs (Sep 12, 2014)

Pinion head said:


> The rear is the most common of the 3 different versions of the '71-72 8.5 A-body, have built well over 300 as posi rears off that particular style housing. The 8.5 A-body rear has a nodular housing and due to the way it was cast, has more pinion support than any 10 bolt or garden variety 12 bolt. With stock axles in an auto 3500-3700 lb A body, many many have been raced weekend after weekend into mid 11's on slicks. For considerably more strength, have upgraded quite a few A9 & A10 axle bearing versions with new 30 spline Eaton carriers & new custom axles.
> 
> Fwiw, in the early to mid 90's , I always ground the big A off these, as well as several other casting numbers. Also reshaped the big square lugs on the bottom to mimic those of an 8.2.


I had an epiphany last nite and realized the reason I can't finds any codes was because I was looking in the wrong place because I thought it was an 8.2. I looked at where an 8.5 stamp would be (pass side axle - front). I ground it down nothing, but finally found it on the axle tube almost facing the ground it was so low. LLB233-1. Which means you are exactly correct, a 1971 Buick 2.73 open 8.5 built on the 233rd day 1st shift. It is a '71 and not a 72 because in 72 they dropped the "B" in the code. So, since it's not a numbers matching car I just got a beefier rear end! I'll put in an Eaton posi unit and should be good to go, thanks.


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