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Technical Is this indeed a GM 12 bolt posi??

Discussion in 'The Hokey Ass Message Board' started by rustyironman, Jul 24, 2017.

  1. rustyironman
    Joined: Mar 26, 2011
    Posts: 464


    I don't have much experiences with this generation of GM rear axles. It is supposedly a 65 Chevelle Posi 12 bolt. (its been put in a much older car). Can anybody tell me for certain from the photo?


  2. Black Panther
    Joined: Jan 6, 2010
    Posts: 1,501

    Black Panther
    from SoCal

    Looks like it from here...
  3. porknbeaner
    Joined: Sep 12, 2003
    Posts: 41,384


    Best I can count it has 12 bolts that hold the cover on and that is a posi carrier.

    All that makes on a 12 bolt is that it takes 12 bolts to hold the cover on. (yes its a heavier rear than a 10 bolt but it is still designated by the bolts that hold the cover on).
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 44,304


    how many bolts hold the ring gear to the differential? I hear there were some oddball BOP rears that had a ten bolt ring gear, in a 12 bolt case. But they're rather rare.

    There might be some stamped numbers/letters on top of one of the axle tubes, which can help with ID. And some stamped numbers on the edge of the ring gear. And maybe a casting date and casting number on the center housing. All of these clues can help us help you figure out what exactly you have, if you care.
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  5. metlmunchr
    Joined: Jan 16, 2010
    Posts: 729


    Yep. Had one of those in an OT 68 Olds 442.
  6. 56sedandelivery
    Joined: Nov 21, 2006
    Posts: 5,911


    The Olds/Pont "12 bolts", had pressed in/plate retained axles, while the Chevrolet 12 bolt axles were held in by "C" clips. There were also Chevrolet/GMC truck 12 bolts that are totally different than passenger car 12 bolts. How does your rearend retain it's axles? I am Butch/56sedandelivery.
  7. Blownfuel
    Joined: Jun 16, 2005
    Posts: 1,262


    Butch, it's got c-clips. You can see one if you expand the picture.

    Sent from my SM-S902L using The H.A.M.B. mobile app
  8. boltupal
    Joined: Dec 27, 2010
    Posts: 260

    from western ny

    The part number on the ring gear will tell you all you need to know. They stamped number on the axle tube will tell the rest of the story. The number of bolts on the cover means little. It should look like this

    Attached Files:

    squirrel likes this.
  9. Blownfuel
    Joined: Jun 16, 2005
    Posts: 1,262


    Looks like the ear and bushing for a GM A body 4 link suspension in the upper right corner of the picture as well, but I can't see enough of it to be sure.

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    Last edited: Jul 28, 2017
  10. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 5,812

    Bandit Billy

    Odd ball? :eek: In the BOP world that's traditional. :cool:

    Still have one in mine. :D 12 bolts outside, 10 bolts inside (saves weight)
    Bills Iphone 2017 991.JPG
  11. rustyironman
    Joined: Mar 26, 2011
    Posts: 464


    Thanks fellas.

    Yes, the axles are held in with clips. Not a 12-bolt truck rear as cover mounting flange is different between car and truck in online diagrams.

    From having a GM buddy look at pics and overall width it appears it is indeed a 65-67 chevelle posi. Ring gear is 3.31. Didn't want to crawl under the thing to find the housing number.

    I'm already having a couple guys who PM'ed me wanting to buy it. What should I expect a real sale price to be?
  12. rustyironman
    Joined: Mar 26, 2011
    Posts: 464


    ^^ anyone have thoughts as to a ballpark price? ^^
    Would like to put a correct width spicer 44 back in the car, any $ I get from this 12 bolt will go toward that. Is it a $50, $250, or $??? rear end?
  13. cavman
    Joined: Mar 23, 2005
    Posts: 627


    A '65-'67 chevelle 12 bolt posi rear will bring good money if complete. I have seen them on the auction site for well over a grand. Rusty ones will bring less than pretty ones. What is in under now?
  14. ssaza25
    Joined: Jun 20, 2010
    Posts: 1,151

    from arizona

    Early 65-67 Chevelle 12 bolt Posi rear ends are hard to find anymore.They are worth over $1000,-$1500 and really clean one bring more.
    henryj1951 likes this.
  15. If all of the mounting brackets to put it back into a GM A-body are still on the rearend, then I think you are looking at near $1500 if all in good shape. Still worth $1000 or more if the brackets are missing. The reason the 65-67 is worth more is because they are narrower than the 68-up, about 1 inch less per side.
  16. big duece
    Joined: Jul 28, 2008
    Posts: 5,725

    big duece
    from kansas

    On the pass side there is a set of numbers to decode. Might have to sand the rust off and see just what it came from and what vintage. rear_late.jpg
  17. squirrel
    Joined: Sep 23, 2004
    Posts: 44,304


    lots of money. I remember buying one in a junkyard in 1978 for $75. Time flies...things change...

    I concur with the 1000-1500 price range, can't seem to find them for less.

    With it possibly being worth a lot, you want to look up those numbers
  18. I just paid $1500 for a clean one, 3:31 posi. Yes the early Chevelle ones were narrower and so more scarce.
  19. henryj1951
    Joined: Sep 23, 2012
    Posts: 2,310

    from USA

    Really, NO S#!T , I just gave, yes GAVE away a 66 chevelle one. ol well, its all good ,
  20. wheeldog57
    Joined: Dec 6, 2013
    Posts: 1,562


    Listen to Squirrel, he knows. . .
    Lots of the Olds musclecars had the 10 bolt carrier in the 12 bolt housing.

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  21. mgtstumpy
    Joined: Jul 20, 2006
    Posts: 7,722



    upload_2017-7-25_20-44-30.jpeg upload_2017-7-25_20-44-39.jpeg upload_2017-7-25_20-45-30.jpeg

    12-Bolt Housings by the Numbers
    The casting numbers for the 12-bolt housings are typically found on the upper rear of the driver’s side of the center section. The casting numbers are simple to decode.

    The first letter is the month of the year; A is January, B is February, and so on. The next digit is the day it was built, and the last digit is the year it was built. For example, a 12-bolt axle that was built on March 28, 1967, is C287.

    On the passenger-side front tube, the stamped axle code designates either:-
    • 1969 and earlier units
    • or 1969 and later builds.

    The 1969 and earlier codes have:-
    • Two letters,
    • Then a four-digit number,
    • followed by a letter, and
    • Possibly a shift number, for which 1 is the day shift and 2 is the night shift.
    And finally, a Posi-Traction number was used.

    For 1969 and later, the code typically features six to eight digits, including three letters, three numbers, and sometimes an additional number and letter. The first two letters indicate the gear-ratio code, the third letter notes the build plant, and three numbers designate the build day from 001 to 365. Sometimes the shift code is stamped, and if the unit has a Posi-Traction, you see a P stamp.

    12 bolt carrier ID last three numbers on the posi unit.
    • 2 series #088
    • 3 series #140
    • 4 series #174
    Casting numbers found to be the most prevalent in Chevelle 12-bolt rear ends:
    • 1965 Chevelle 3859140N
    • 1966 Chevelle 3875745N
    • 1967 Chevelle 3894939NF
    • 68-69 Chevelle 3917124NF
    • 1969 Chevelle 3959038NF
    • 70-72 Chevelle 3969278NF
    squirrel and custom_line like this.
  22. models916
    Joined: Apr 19, 2012
    Posts: 380


    BOP does not have C-clips.

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