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rear axle help?


So I have a 1970 Pontiac GTO built in the Oshawa plant and came with a factory installed 12 bolt. It currently contains a posi carrier with 4:11 gears. I am trying to find out what the factory original gears were? Here is a pic of the axle front passenger side axle tube. Thanks gang.

 



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A Poncho Legend!

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None of my books for Lemans show that code, or anything close.

I did find 69 Chevelle axle CY (which would fit right in to that car) as being a 3.07 diff.

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Carl Stevenson wrote:

None of my books for Lemans show that code, or anything close.

I did find 69 Chevelle axle CY (which would fit right in to that car) as being a 3.07 diff.


Interesting that his Oshawa built GTO has a 12 bolt diff.  I'm not a GTO expert, but suspect someone has changed the diff at some point.



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Link I found says it's also a Chevelle  3.07 rear end.

http://chevellestuff.net/1967/rear_axle.htm

There should be a letter after the numbers to tell which plant the rear end came from.

CHEVELLESTUFF © All Rights Reserved



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Only 455 powered 1970 GTOs received the 12 bolt as well as 71-72 but in Oshawa, they installed 12 bolt in a lot of cars. I had an Oshawa built 1972 Lemans 400 with the factory 12 bolt.



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I knew the 72's came with a 12 bolt but I haven't seen one in a 70 before.


However, the Canadian parts book does list 70-72 Lemans with a 12 bolt, just nothing with a code anything like that.

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So this may not be the original rear to the car. This has a date of June 16 and this car shipped in October. I'm pretty sure that Pontiac didn't have a dedicated 12 bolt they produced and I'm sure that the 455 Pontiacs came with the same 2 bolt from Chevelles. I too heard that Oshawa installed Chevy 12 bolts into Pontiac GTO's. I figured there would be some export experts here, thanks.

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Any way to know how many splines on the axles without pulling the axles?

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pull the rear cover and remove C clips and pull axle out a little ?    long time since I did that 



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360Rocket wrote:

Any way to know how many splines on the axles without pulling the axles?





A Chevy style 12 bolt like this one should be 30 splines.

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Back in the original post is there a hint of a 1 after the other numbers?

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Looks like the last letter is a B for Buffalo New York.

Al

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Lot's of Oshawa cars got the 12 bolts.Also have seen Lemans with the diff braces.Have removed them from wreckers.

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I'll get under and double check the numbers again but yes I believe that is a "B" and I'll check for more numbers as well.

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So did Pontiac make a specific 12 bolt of their own and labeled as Pontiac 12 bolts? Or did they just install Chevy labeled 12 bolts for obvious cost reasons? I remember from past GTO's I had owned that had 10 Bolts were considered a BOP rear for Buick Olds and Pontiac but not sure how a 12 bolt is categorized?



-- Edited by 360Rocket on Friday 15th of December 2017 09:32:26 PM

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I think the only 12 bolt that ever came in GTO/Lemans was this style, classified as a Chevy 12 bolt.

12 bolt.jpg

Cutlass had a different cover on their 12 bolt, the internals were different as well. I'm not sure but I think Skylark may have used the Cutlass style 12 bolt as well.

Oh, and some Cutlass's came with the Chevy style 12 bolt!





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Poncho Master!

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The 1970 GTO had the option for the Chevy 12 bolt or Type C axle, it was standard on the 455 cars as mentioned earlier. If your car is Canadian built or imported and it had an axle upgrade from the factory it would show that on the parperwork from VVS in Oshawa. If it is a US import the paperwork is available through PHS in the US. The information is readily available if there is no axle information on the paperwork based on engine size, transmission, etc.

One thing of note the 12 bolt posi carrier does have a "P" if it were factory installed in a Pontiac, including the Beaumont.



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Here's a question from left field, but I know it's a longshot:  Do you have the Protect-O-Plate for your car?   If so, it lists the engine, transmission & differential stampings on it.  That way you could determine if the diff is original to the car.

I have the Protect-O-Plate for all 3 of my cars.   Here's an example:

1970 Protect-O-Plate.jpg

 



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I don't have the Protect O Plate but I do have the PHS and I am surprised it doesn't list the rear option on the PHS OR the replica window sticker I also have. I do have the Diff cover in the above photo. I might have to grab the Canadian version of PHS. The car was delivered and sold to a dealership in Cincinnati Ohio.



-- Edited by 360Rocket on Saturday 16th of December 2017 06:53:27 PM

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I don't think the Canadian documents will help you out with the diff. It may say G80 posi, or have a code if it was ordered with an optional gear ratio, but it won't list actual ring gear size.

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It's still interesting that it shows a 1969 CY code. Even though the car was produced in the 1969 calendar year, it should have a 1970 model year code.

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70 Parisienne hardtop
72 GMC Sierra

 

 



A Poncho Legend!

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I think it's a pretty safe bet this diff is not the original with this car. The dates don't make sense at all.

And certainly it would not be unusual for an A body to have had a diff swap in almost 50 years, especially since it has 4.11's too.

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