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Technical 12 bolt rear end

Discussion in 'The Hokey Ass Message Board' started by Crshndbrn, Apr 14, 2014.

  1. Crshndbrn
    Joined: Feb 26, 2014
    Posts: 34

    Crshndbrn
    Member

    What vehicles would be a good place to find a 12 bolt 5-4.5 rear end that would be a proper width (or close) to put under a 1955 C3100 step side?

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  2. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    4.75" maybe? One of the late 60s Chevelle rears would probably be just right. Kind of valuable these days though.
     
  3. Crshndbrn
    Joined: Feb 26, 2014
    Posts: 34

    Crshndbrn
    Member

    Ah geeze, yes 4.75. Wow, not sure what I was thinking of.

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  4. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    The 10 bolt rear from a 71-81 Camaro/Firebird is almost as strong as the 12 bolt, and much more easier to afford.
     

  5. Shamus
    Joined: Jul 20, 2005
    Posts: 1,247

    Shamus
    Member
    from NC

    I have '80 Camaro 3.42 posi "big 10" bolt under my 1st series '55 w/255R60s on 8" rallies & it works perfect; also have similar (think it's a '79) under a '56 3100 not finished but fits great. Both have leave springs from Chassis Engineering (1st series) & TCI - rides great.
     

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  6. Crshndbrn
    Joined: Feb 26, 2014
    Posts: 34

    Crshndbrn
    Member

    Hmmm... Maybe a 9" instead. Just spit balling right now.

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  7. Hotrodbuilderny
    Joined: Mar 20, 2009
    Posts: 1,646

    Hotrodbuilderny
    Member

    As Squirrel said go with an 8.5,just as strong as a 12 bolt,10 7/16 bolts as compared to 12 3/8 and the pinion is identical,weak spot are the axles 28 v 30 spline but you can use the side gears out of a lot of pick ups which had 30 spline.
     
  8. Mr48chev
    Joined: Dec 28, 2007
    Posts: 33,861

    Mr48chev
    ALLIANCE MEMBER

    I'd have to agree with Squirrel, unless you just fumble onto one at Pick a part on discount day those 100 dollar 12 bolt Chevelle rear ends are now up close to 4 figures price wise in a lot of places for a good 12 bolt posi of that width. The Chevelle and Chevelle size car brigade have latched on to most of them and run the price up to boot.
    I've got a disk brake 10 bolt posi out of a late 70's Trans Am going under my 48 that is slightly over 60 inches wide. That's a little wider than the stock Task Force rear at 58 and something but that just gives tire clearance with some tire and rim combos.
     

  9. agreed....good deals on these and very stout...chevelle twelve bolts anywhere from 200 to 1800 depending...
     
  10. mechanic58
    Joined: Mar 21, 2010
    Posts: 681

    mechanic58
    Member

    I've swapped late 60's and early 70's truck 12-bolts into these vintage trucks - both 6 and 5 lug versions - but you can buy axle any pattern you want or even re-drill the axles you have. Those truck 12-bolts are almost give-a-ways in most cases. I think I paid $75 for the last one I picked up for this purpose and it was even clean, painted and had new brakes on it!

    The 8.5" 10-bolts are by far the cheapest and easiest route though. Those axles actually use all the same bearings that a passenger car 12-bolt uses (the truck 12-bolt is different, actually lighter duty). You can even put passenger car 12-bolt guts into an 8.5" 10-bolt housing with minor modifications. The only real problem with these 10-bolts now days is that they're also getting scarce. Seems like the weeds are still sitting full of old pickups that have those 12-bolts in them - but everyone has rounded up all the 70s vintage camaros and novas that had those big 10-bolts in them and squandered their parts or hauled them off for salvage.
     
  11. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    thru 69 they are the right width, and 6 lug. 70 is wider, 6 lug. Starting 71, they are wider and 5 lug, but 5" bolt circle, not 4.75" that "normal" chevy cars use.
     
  12. Crshndbrn
    Joined: Feb 26, 2014
    Posts: 34

    Crshndbrn
    Member

    I tried for the 10 bolt from the firebird I'm picking the sub from, but it's outside my financial reach right now. Time to save pennies and dimes, but now I know what to keep my eyes peeled for. Thanks for all of the suggestions guys!

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  13. joel
    Joined: Oct 10, 2009
    Posts: 2,467

    joel
    ALLIANCE MEMBER

    I just built an 8.5" 10 bolt from a '76 Monte Carlo. I had it narrowed to 68-72 Nova spec, used an auburn posi with 30 spline spiders and Guess What? 12 bolt 30 spline axles were an exact fit. ( Mosers, but same-o same-o ). Trucks up to '87 had the spring loaded posi clutches, while the later ones were weaker ( so I've heard ).
     
  14. 1971BB427
    Joined: Mar 6, 2010
    Posts: 8,717

    1971BB427
    Member
    from Oregon

    Hmm? I thought they didn't get wider until '73 with the new body change? I have a '69 Suburban that a later 12 bolt bolted right into to make it 5x5" bolt pattern. Same width as the old 6 bolt rear.
     
  15. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    no, it was 1970. I can scan the parts book if you'd like....the difference isn't much, less than 2" overall width. could be the 69 had a 70 rearend in it?
     
  16. dirtracer06
    Joined: Sep 29, 2009
    Posts: 198

    dirtracer06
    Member

    I ran a '76 Monte 8.5" in my circle track car for 16 seasons, broke 2 right side axles, once after being slammed into the wall and once when the car was sitting sideways and was hit directly in the right rear wheel.
    I never broke the gears or bent the housing, the matching spare rearend i bought 10 years ago now resides under my 34...not as tough as a ford nine inch...but a good street unit with a good selection of parts available.
     
  17. Crshndbrn
    Joined: Feb 26, 2014
    Posts: 34

    Crshndbrn
    Member

    I was looking today, will probably have to do something with the springs. Looks like it would hit with the worn out originals. How much did you pay for springs?

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  18. 1971BB427
    Joined: Mar 6, 2010
    Posts: 8,717

    1971BB427
    Member
    from Oregon

    Not sure Jim. A lot can happen to these old trucks over the years. Do you have an OA width on the later 5x5" pattern rear axle?
     
  19. squirrel
    Joined: Sep 23, 2004
    Posts: 55,931

    squirrel
    Member

    the early axles are 30.x" long, the later axles are 31.x" long, according to the book. I think that makes the rears either 61ish or 63ish inches drum to drum
     
  20. JoshVD-port81
    Joined: Dec 12, 2016
    Posts: 7

    JoshVD-port81

    I'm looking at a 1965 to 1970 Chevy Impala Biscayne 12 Bolt Posi Rear End will it fit u set my 1954 Chevy delray 210? Thanks for any info


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