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Would anyone happen to know the stampings on the axle tubes of a 12 bolt rearend from a 70 nova? Could it be "OS"?? and if so what gear ratio is that? Thanks in advance.
 

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firebird would be a 3.07 open non posi rear That is probably what it is. Check the width of the housing. 55 1/4 is or 53 1/4 backing plate to backing plate...also get us the casting number is it 396934NF then it is a camaro firebird 12 bolt 1970 housing.

3894860NF is a nova camaro 1967 -1969 year
 

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Casting number is 3969341
My number was wrong and I forgot to list the '1' I put 396934 and it should have been 3969341. Sorry. You have a 1970 camaro housing as I suspected. Some one may have moved the perches in a few inches to make it fit the nova rear. That is why I said measure the width of the housing...that will telll the whole story.

The code is COS some times on 1970 rears the C is left off it os a open 3.07 rear housing...what is inside who knows? Open it and find out. If it is an original GM gear the pinion head (flat top) will have all the info you need. Can be a little difficult in the car to see. all the fluid must be out and use brake cleaner to clean the top of the pinion gear for the stamped numbers. It will give you the date (month and year) the number of pinion and ring gear teeth (14 43) and tthe pinion part number.

You will not find the number on the ring gear because they are located on the back of the ring gear machined surface...???? Who goofed with that one? lol. Totally usless area to put info. lol. Hope this helps. Jim J D Race.com
 

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You will not find the number on the ring gear because they are located on the back of the ring gear machined surface...???? Who goofed with that one? lol. Totally usless area to put info. lol. Hope this helps. Jim J D Race.com
???????
3.08 gears found in an early build 64 El Camino.

 
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