12 bolt type 0

Discussion in 'Got gears?' started by rack-attack, Oct 21, 2009.

  1. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    :laugh: :laugh: Yup, it's an addiction, what can I say, I need my V8 Fix every day.:TU:
     
  2. monzaz

    monzaz Jim

    Yah, but your on the other buick sites too. Then again look at me talking...lol :) You the MAN!
     
  3. BrianTrick

    BrianTrick Brian Trick

    Yes,the 12-bolt O-axle,or also known as the 12-bolt Olds,is unique to itself,& parts for them are scarce & fairly costly. They were made from 67-70. Most of them were 28-spline bolt-in axles,but they did make 31-spline units for the late-67/68 ram-air cars.The pinion is 27-spline,just like the BOP 8.2's.The posi units use the same clutches,side gears,& spider gears as the GM 8.5" posi units,but the dimensions of the carrier & bolt spacing is different. Reider Racing was making new units by remachining 8.8" Ford units,then soldout to DTS. I have machined my own from Eaton blanks,& I have also made my own full spools for those die-hard Olds purists. I would suggest investing the money into a 71-72 8.5" 10-bolt,& leave the O-axle to the restoration guys.They can handle the power though.You would need a longer driveshaft,as the O-axle has a shorter pinion snout.
    Here are the posi carrier numbers & series:
    # 673 = 2:56,2:78 28-spline
    # 671 = 3:08,3:23 and the Richmond 3:42,3:90,4:10 28-spline
    # 588 = 3:42,3:91,4:33,4:66,5:00 28-spline
    # 672 = 3:42,3:91,4:33,4:66,5:00 31-spline

    You can also install the Powertrax #1920LR unit into the O-axle open carriers.
     
  4. monzaz

    monzaz Jim

    not all the info is correct ....

    8.5 and 12 bolt olds side gears are not the same.

    12 bolt olds uses a 60 degree spline and the 8.5 10 bolt has a 45 degree axle spline cut.

    SO you can use the 8.5 power trax in the 12 bolt olds...But you will need to use 71 72 axle shafts.

    Take care, Jim
     
  5. BrianTrick

    BrianTrick Brian Trick

    Yes,as long as you have a 1970 housing,as that was the only year they had the same SET-9/712146 bearing/seal design.
    I guess I should have said that the inside dimensions of the carriers are the same,but some might get confused.
     
  6. stage1 Rick

    stage1 Rick Member

    Hi guys.... just reading your posts on the olds 12 bolt...
    I have a '71 gs 455 with a olds 12 bolt, in it....it was built in Flint in Dec '70 and was sent to Canada.... It has 3.42 posi.... and Canadian GM parts book show one listed...
     

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