Hello to all,, we are new to this site.. We puchased a 12 bolt rear today for our 69 nova.. ONly to get it home and did some research to find out that it is out of a 1970 camaro,, COS.. And the dimensions are not the same. Instead of 'making' it work,, would it be best to try and get our money back? and keep loooking?.. The rear that is in the car is a JD designation and we have yet to find out what it orginally came out in or gear ratio.. Pretty sure its an 8.2... but we dont know..

An 8.2" ring gear would make it a ten bolt rear end, not a twelve bolt. 1970 up (to 1981) had a one inch wider rear end with the spring perches welded at a slight angle three inches further apart compared to the '69 which had a 60 inch width backing plate to backing plate (the one that fits the Nova body). The spring perches are 42-1/2 inches from center to center. Also the pinion is offset 1/2 inch from center, which means that it will be 29 1/2 inches from the center of the pinion to the end of the right axle and 30 1/2 inches from the center of the pinion to the end of the left axle.

Big Dave

My 72 10 bolt is a JD. I don't know if it's the original, but it seems to be. JD should be from a 75 (?). A JD rear in 75 was a 3:08 open, which is what mine is. Could have been switched I guess or mismarked. Best bet is to hope for a refund and start over (in my opinion).

Check out this site: http://www.novaresource.org/axle.htm


Dan (happy hunting):)

Dan thanx for the info.. And the website for the difference in 10 bolts.. very helpful.. Yes the one in our nova is an 8.5 according to the large tabs on the bottom.. Im wondering if a later like posi carrier will fit in this housing.. I have a later 8.5 dont know what its out of.. designation PZ... still has the posi tag on it.. WEll anyway thanx for the very helpful info..

If you have an 8.5" already no need for a 12 bolt. Sell it to a Camaro owner if you can't get a refund.

The PZ code on your 10 bolt would make it a 3.42 open and was used from 75 - 77. Thats not to say it hasn't been changed and a posi added.
big gear head from this site built a 3.73 posi rear end for me and the codes show it to be 1979 2.42 open. Pull the cover and see whats inside.

Posted a reply to your post on the Camaro board. What do you want for the 12 bolt? Build the 8.5 with a 30 spline Eaton posi and 30 spline axles. It will be almost as strong as a 12 bolt if it is set up right.