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Technical GM 10 Bolt 8.75" Rear End Parts

Discussion in 'The Hokey Ass Message Board' started by rodknocker, Jul 14, 2014.

  1. rodknocker
    Joined: Jan 31, 2006
    Posts: 2,267

    rodknocker

    This past weekend I had a GM 10 bolt 8.75" rear end just about given to me, to put in my '49 3100, but it's in need of a few things as its been sitting outside for a few years. This is appartently the rare rear en that aftermarket parts are few and far between. I beleive the internals are good but I need to put a complete set of brakes starting at the backing plates on the rear. The housing is too rusted to get numbers off of. I know by counting the teeth it has a 2.56 ratio, and its a posi unit. My truck sits on an S10 frame so I figured this will do a few things for me, I need better highway speeds, and its wider to fill the rear fenders. If anyone knows where to find parts for the housing, or what other rear ends have the same backing plate/ drum set up it would be greatly appreciated.
     
  2. BucketHeadBart
    Joined: Jan 13, 2014
    Posts: 59

    BucketHeadBart
    Member
    from illinois

    I just took a good set of drum brakes complete w backing plates off of a GM 10 bolt. I dont think I threw them out. If I still have them , they're yours if you want them. Dont know if its an 8.75 or not
     
    Last edited: Jul 14, 2014
  3. rodknocker
    Joined: Jan 31, 2006
    Posts: 2,267

    rodknocker

    Bart, I would be happy to take them as long as they fit, I don't want to waste your time. I know the diff covers are different, I'm wondering if anyone knows for sure.
     
  4. 270283
    Joined: Jun 11, 2006
    Posts: 389

    270283
    Member

    As far as I know, the biggest 10-bolt was the 8.5 rear. The 12-bolt was 8.875. If it is in fact a Chevy 8.5, parts should be easy to source as it was used from 1972 until the mid-eighties in various Chevies.
     
    Last edited: Jul 14, 2014
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  5. joel
    Joined: Oct 10, 2009
    Posts: 1,518

    joel
    ALLIANCE MEMBER

    I know the GM 8.5 10 bolt, 8.2 10 bolt, and Chevelle nova Camaro 12 bolt baking plates brakes will interchange. The 8.5 10 bolt was used in Monte Carlo etc. from about ' 75 and had larger brakes than nova and Camaro.
    The 8.5 10 bolt carrier( ring&pinion) was used in 1/2 T trucks up to '88, but the brakes could be different.
     
  6. BucketHeadBart
    Joined: Jan 13, 2014
    Posts: 59

    BucketHeadBart
    Member
    from illinois

    I was just Looking at a chart for covers, it looks like mine is the 10 bolt 8.2 . I don't know if they will fit or not.
     
  7. rodknocker
    Joined: Jan 31, 2006
    Posts: 2,267

    rodknocker

    Please read this article.
    http://purplesagetradingpost.com/sumner/bvillecar-4/gm 7 1-2 vs gm 8 3-4.html
    The 8.75" 10 bolt is the rear I have the cover has the half moon cut outs level with the axle.
     
  8. rodknocker
    Joined: Jan 31, 2006
    Posts: 2,267

    rodknocker

    I just measured the axle bearing bolt pattern, the top studs are 3" apart, the bottom are 4" apart. and vertically are 2.5", is that a standard 10 bolt pattern?
     
  9. 270283
    Joined: Jun 11, 2006
    Posts: 389

    270283
    Member

    I stand corrected. After reading the article, and the excellent link in the article, I do vaguely remember talk back then of a 12 bolt in a ten bolt housing. Just another memory lapse.
     
  10. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547

    stimpy

    thats the coil spring axle for the boats . IIIRc they use 12" brakes double check your measurements [​IMG]
     
  11. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547

    stimpy

    get a picture of the mounting flange as you might have the weird ones .
     
  12. rodknocker
    Joined: Jan 31, 2006
    Posts: 2,267

    rodknocker

    Here's a picture hopefully you can tell the set up, though I'm starting to loose faith that I can find parts, my online searches are turning up empty.
     

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  13. rodknocker
    Joined: Jan 31, 2006
    Posts: 2,267

    rodknocker

    Sorry guys I think I'm a clueless donkey. I think I might have a mid 60's BOP rear.according to this website http://www.jdrace.com/diff_id/10bBOP_Early.htm especially since my bolt pattern is 5 on 5". So I may be in luck, as far as finding parts. I've never been familiar with rear axles, you live and learn I guess.
     
  14. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547

    stimpy

    quickest way to ID it , does it have a flange ( like a ford 8.8) or a u joint cup on the pinion , if its a flange its a 8.75 from the 70's , the HD ( police ,taxi, tow , large motor ) version of the 8.75 was a 5x5 pattern and its a junk yard only part unless you can find someone willing to help you convert to discs ( they will need the axle offset to the flange plus some other measurements , I was reading its also a truck flange , but truck brakes supposely do not work due to the different offset .
     
  15. rodknocker
    Joined: Jan 31, 2006
    Posts: 2,267

    rodknocker

    It has the u joint set up on the pinion.
     
  16. captmullette
    Joined: Oct 15, 2009
    Posts: 1,929

    captmullette
    Member

    ive got a 8.5 truck rear in my A , I think its a '70 had it shortened moser axles it came with a posi I just change the ring and pinion from a 3.73 to a 4.56. the mech. said the 8.5 is a good strong rearend. if you need a 3.73 ring and pinion mines for sale $100. the gear is fairly new, maybe 30 miles on it, it comes with a new bearing kit......good luck
     

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