GM B-Body Forum, 77-79 Caprice/Impala Forum

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GM B-Body Forum, 77-79 Caprice/Impala Forum

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GM B-Body Forum, 77-79 Caprice/Impala Forum

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GM B-Body Forum, 77-79 Caprice/Impala Forum

A forum for all the owners and enthusiasts of General Motors B-Bodies from 1965-1996, but dedicated to the owners of 1977-1979 Impalas and Caprices. Join up now!

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    GM 8.75" 10/12 Bolt

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    Post  GM B-Body Forum Mon Mar 17, 2014 3:17 pm

    Thought i should write something about this odd ball rear end. The GM 8.75" 12 bolt has an 8.75" ring gear mated to the carrier with 12 bolts. Its also called a 10 bolt because the cover has 10 bolts, but this is actually a 12 bolt. I would call it a hybrid, its like the child of a GM 8.5 10 bolt and a GM 8.875 12 bolt. It was used in the mid to late 70's B-Bodies, usually the wagons, or ones equipped with HD options such as towing. This rear end is very strong, but yet it has no aftermarket because it was only produced for a couple of years. Ive only seen two in my whole life, both had 2.41 ratios, and one had posi and the other did not. It came with a 28 or 31 spline axle, and has a 30 spline pinion and 1-1/4" pinion nut, the same specs that the 8.5's have.
    The cover looks like this:
    GM 8.75" 10/12 Bolt 8_3-4_10
    Heres one out of a 79 impala sedan
    GM 8.75" 10/12 Bolt 2013-114

    1979 Caprice Sport Coupe, 400hp Vortec 350, Th350, GM 8.5 w/disc brakes, 3.90 gears Detroit Truetrac, 2.5" stainless duals w/ x-pipe, Dynomax race bullets.
    1984 Caprice Sedan, 305 motor, 700r4
    1978 Caprice Sedan, 305 motor, th350
    1993 L99 Caprice, 4.3 v8, 4l60 trans
    1972 Ford F-100, 302 windsor, c4 trans
    2001 BMW E46 330i, 3.0L
    GM 8.75" 10/12 Bolt 20150410
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    Post  78i6belair Wed Dec 31, 2014 5:15 pm

    Im almost 100% sure this is what my 78 Bel Air has and its a 2.73 ratio.
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    Post  Myloth Wed Dec 31, 2014 5:32 pm

    I have never seen one either that I knew of . I did read about it though diff list for GMs and GM did make quite

    few oddball rears like the Aussie Borg Warner 9 bolt . Some pretty strong but this one like the Aussie is a victim

    little to no aftermarket like the 8.2 rears of old. Did you own one of those or seen it in someone else's car?
    Sweet Seventy9
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    Post  Sweet Seventy9 Wed Dec 31, 2014 8:45 pm

    A long time ago I almost bought one of those from Garys U-Pull it in Binghampton NY for $75.  It was in an Impala I got some parts out of.  
    I was like WooHoo a 10 bolt posi rear for $75!!!  (10 bolt, LOL  Laughing )  I was THIS close to buying it until I found out it had 2-something gears.  
    Seeing as I'd never heard of a GM posi rear with anything higher than a 3 gear, I figured it had an open diff and someone welded the spider gears to make it a posi so I passed on it.  I've never seen another one until today.

    Now I'm wishing I got it anyway just to be different.  I'd have one cool-assed 12 bolt rear end!
    The way I see it is, if I can buy a HP cam for my Caddy 500, I'm sure somebody, somewhere makes parts for them.

    *edit: Yeah, post #427 (giggles) Tri-Power!

    1977 Impala Landau x1
    1977 Caprice Coupe x3, Sedan x3
    1978 Impala Landau x1, Sedan x2, Station Wagon x1
    1978 Caprice Landau x1, Caprice Coupe x2
    1979 Impala Coupe x2
    1979 Caprice Coupe x7, Landau x4, Estate Wagon x1
    1981 Impala Coupe x1
    1983 Impala Sedan x1
    1983 Caprice Sedan x1
    1984 Caprice Landau x1, Sedan x1
    1985 Caprice Coupe x1, Landau x3, Sedan x4
    1986 Caprice Coupe x1, Landau x1
    1987 Caprice Landau x1, Sedan x4
    1989 Caprice Sedan 9C1 x4
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    Post  terry cronk Tue Aug 25, 2015 10:12 am

    I have one of these in my 79 Caprice.  And just this last weekend I saw another at a car show out of a 78 Impala.

    According to the owner he had a 3.73 gears installed along with a posi. case.  

    Its a B.O.P. 8.2 only.   Not the Chevrolet 8.2.  

    I can go on Ebay and get anywhere from 3.08 to 4.11 gears and posi. cases.

    The splines on the axles are 28.

    For those who want and can't find.  Try Ebay in differentials and search for 8.2 BOP.

    The fellow who showed me his car w/8.2, said he had 7000 miles on it and about 100 runs at the dragstrip.

    He has a 406 small block w/700R4.

    What do you think those Pontiac GTO, Olds 442 and Buick GS ran. Some had 12 bolts. Others had 10 bolts(8.2).

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    Post  cammrjeff Tue Jan 26, 2016 9:54 am

    Its funny what diffent parts people are used to, the 8.75, and earlier 8.875 axles are what have been under a lot of my cars, but they were 78 B-body Wagons, 76 A-body Wagon, and the 8.875' are in my 73 Lemans Wagon, and my 71 Catalina Sedan.

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    Post  kalspach Tue Apr 26, 2016 3:43 pm

    Just an FYI. I received a new axle for my 8.75" 12 bolt today from Dutchman Axles in Idaho. $170 for the axle, bearing and seal + shipping. Their listing for 1977 Impala wagon showed a 31 spline but mine is a 28. They custom built it based on the measurements from my damaged axle. Their listing for a 1975 Caprice convertible was really close to my Impala except for the button width. It looks like a very nice part and the rep was a nice guy.

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