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Discussion Starter #1
Guys,
I traded a 10 bolt rearend to a guy 2 years ago for a 12 bolt (he traded cause the rear end I had was a bolt in to his 56 Chevy). I can't figure out what this 12 bolt is out of. Here are the details (please help I am trying to sell it and need details).

Axle flange to axle flange 63 1/2", backing plate to backing plate mount 58 3/8" it has leaf spring perches that are 38" center to center.

Casting numbers are as follows B116 (on the back side), GM6 (top of front side), 3852980N (lower front side).
 

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Hey Royce, I'm at work (on lunch break of course, your tax dollars at work..) and did a search for GM differentials. Our system is extremely tight but I did find the site below that would indicate the code GM6 (RPO Code ?) is a GM truck rear with a 4.22 ratio. I say truck mainly because of the ratio and the site URL has trk in it, he he.

There were some other interesting sites that may decode the 3852980N code you listed as well, but I was limited there as well.



[url]http://www.drivetrain.com/GMtrkratio_posidata.html
[/URL]

Good luck, Larry

That link isn't working when I try it from here, if you have problems just go to the drivetrain.com home, go to the bottom of the page, then to the "Free" section for "What ratio do I have" link.

Guess I need some practice inserting URL's.
 

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I found that the Code "3852980N" 12 bolt posi-traction differential was installed in many different cars in the mid to late 60's.
Axle flange to axle flange 63 1/2", backing plate to backing plate mount 58 3/8" it has leaf spring perches that are 38" center to center.
An axle search with the wheel mounting measurement you gave listed no results. Chevy trucks measure 62 inches.

An axle search with a 58 inch backing plates measurement gave me:
'61 Chevrolet Impala, '65 Cadillac, '66 Buick Wildcat, '66-67 Chevrolet Big Car, '69 Oldsmobile 88.

An axle search with spring perches 38 inhes on center resulted in nothing either.

Either a large leaf sprung car, or truck would be my best guess.
The stamped code would tell the gear ratio, year, vehicle, and when & where it was made.
 

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Discussion Starter #6
Guys,
Thanks for the input. The gear ratio is 3.31. Don't the truck rear ends have a different cover/shape than car rear ends? It is definetly a round cover. I do have pictures and I will post them (I have to reduce the size cause they are too big).

Did the early coil spring cars (don't have one handy to look at) have mounting ears on the "center" section? My thought is that this rear end is out of a wagon, Chevelle, Monte Carlo or Impala and someone removed the coil spring mounts and welded on leaf spring mounts. The guy I traded had it in his 56 Chevy (but was too wide for the rims he was using).

I will work on posting a few pictures.

Thanks,
Royce
 

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camaroman7d said:
Guys,
Thanks for the input. The gear ratio is 3.31. Don't the truck rear ends have a different cover/shape than car rear ends? It is definetly a round cover. I do have pictures and I will post them (I have to reduce the size cause they are too big. Royce
Yes the truck rears do have a different shape and they aren't as strong as the 12 bolt car rears. The reason being the truck rears have a smaller diameter pinion shaft than the car rears.

this shows the two, second and third column. http://www.differentials.com/pdfs/46.pdf
 

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Discussion Starter #8
Ghetto,
Exactly as I thought. It is a car rear end. I didn't want to grind/sand the paint off (I am selling it) to see if the stamp is on the front of the passenger side tube.

What photo editors do you guys use? I can't get my picture small enough to fit here. I guess I should change the setting in my camera.

Royce
 
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