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    How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

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    How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

    Post  GM B-Body Forum on Wed Dec 10, 2014 10:06 am

    Ok thought id make a topic on rear end identification, most folks want to know what they have or what to look for when buying one.
    The most common ones youll encounter are the 7.5" and 8.5" rears. The 8.5" has been dubbed the GM Corporate rear end.
    In the 90's and 2000's GM put a slightly bigger ring gear in in both, they were now the 7.6" and 8.6" rears, nothing to even get excited about, but they are still the same rears.
    Heres a pic the differentiate the two:



    And a couple pics of them in person:

    The 7.5"


    The 8.5"


    The quickest way to differentiate is the covers, the 7.5 is more oval where the 8.5 is round

    And both side by side







    Now for the less common and very rare 8.75" 12 bolt, i made a topic dedicated to this one since its so special lol https://www.gmbbodyforum.com/t172-gm-8-75-10-12-bolt


    Now the more common GM 12 bolt 8.875"
    You wont find this in the 77-96 b-bodies but thought id still put it here, in fact theres a good article about them. They were found in both cars and trucks from the 60s and 70's. Its been said that a 12 bolt from a passenger car is stronger than a truck 12 bolt and i cant remember exactly why.
    http://www.hemmings.com/hmn/stories/2009/06/01/hmn_feature30.html


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    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
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    HeavyChevy77
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    Re: How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

    Post  HeavyChevy77 on Wed Mar 25, 2015 7:24 pm

    I'm not sure which axle I have it looks like the 8.5" axle has the rounder cover the bulge on the left but what has me sold its 8.5" is that it has the 90 degree ears on the bottom not the thin points ears like the 7.5"
    It also has a sway bar , don't know if the 7.5" came with one, the car used to be used for towing so idk if it was upgrade in its lifetime. I'm hoping it is cause I'll swap axles on Friday if that's the case. Check the photo and let me kno what u guys think.




    I wanna slap in the axle I have already
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    Re: How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

    Post  GM B-Body Forum on Wed Mar 25, 2015 7:42 pm

    Yeah those are both 8.5s, and sway bars came with both the 7.5 and 8.5


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    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
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    Re: How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

    Post  HeavyChevy77 on Wed Mar 25, 2015 7:46 pm

    f**k yea she going under the knife on friday 
    damn thanx bro i was wondering about the driveshaft but then the arms and diff were the same size and i was getting confused, thinking its a 7.5" not a 8.5" 
    did some 77 caprices roll outta gm factory with8.5" installed?
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    Re: How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

    Post  GM B-Body Forum on Wed Mar 25, 2015 8:06 pm

    Yup some of them sure did, i think in '75 is when the 8.5 came out, i cant remember, but yeah man you wont have to do anything to the drive shaft but slap it in!


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    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
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    Re: How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

    Post  HeavyChevy77 on Wed Mar 25, 2015 8:26 pm

    ughh if i didnt have a midterm tomorrow id skip skool and swap it tomorrow but i get one week off so it'll be plenty of time to do it 
    by the way what did u do for the parking brake?
    did it bolt right up or did u have to mess with it? thanx again
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    Re: How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

    Post  GM B-Body Forum on Wed Mar 25, 2015 11:45 pm

    i completely took it off, they had cut the cables when i got the rear end at the junk yard so id have to find donor cables, so i just took it all off, never use them anyway, and my car dont have to pass inspection because of its age. It only took me about 4 hours to do the rear end swap.


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    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
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    Re: How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

    Post  HeavyChevy77 on Thu Mar 26, 2015 12:58 am

    Well I guess I can maguyver something thing up 
    How much u think that old axle is worth just a 8.5" open diff 2.mid's gears with 9 1/2" drums ..maybe 100$ on Craigslist?
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    Re: How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

    Post  GM B-Body Forum on Thu Mar 26, 2015 8:33 am

    maybe, i know mine was worth 40 bucks in scrap metal but mine was the 7.5, i knew no one would buy mine and plus it was shot. I think it was over 300 pounds, that was with the control arms and the sway bar


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    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
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    Re: How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

    Post  Gooched78Caprice on Thu Mar 26, 2015 10:32 am

    HeavyChevy77 wrote:I'm not sure which axle I have it looks like the 8.5" axle has the rounder cover the bulge on the left but what has me sold its 8.5" is that it has the 90 degree ears on the bottom not the thin points ears like the 7.5"
    It also has a sway bar , don't know if the 7.5" came with one, the car used to be used for towing so idk if it was upgrade in its lifetime. I'm hoping it is cause I'll swap axles on Friday if that's the case. Check the photo and let me kno what u guys think.




    I wanna slap in the axle I have already

    This looks awesome, great upgrades! I've been keeping an eye in the local yard at the different rears and have been able to help a guy looking for his 86 caprice with the information found here on the rears. Great info and I can't wait to see it all in. Reading through your different post Heavy, I wish we could see what this monster would become if you didn't live in CA. However, It might be for the best for your safety and others on the road. Laughing
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    Re: How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

    Post  Myloth on Thu Mar 26, 2015 10:47 am

    The 7.5 I pulled out of mine weighed about 45lbs lighter than the 8.5 it replaced and without anything attached I

    could easily pick it up myself, pretty light duty stuff. You know I think there is some confusion on the 8.5 8.625s

    Last night I was reading and GM didn't make 8.625s till 99 and the main difference is the carrier bearings are larger

    and if you swap a 8.625 differential (Like a Detroit Locker) into a 8.5 you need non stock bearings specifically for

    that swap. If anyone can add to this or clear anything up please do.
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    Re: How to ID your rear end- GM 10, 12 bolts 7.5, 8.5, 8.75, 8.875

    Post  HeavyChevy77 on Thu Mar 26, 2015 6:43 pm

    Thanx gooched78 ..if I didnt live in Cali I'd already have header straight pipe with a nice slightly lopey idle cam  and some nitrous etc,etc,etc... *sigh*i can only dream ..,or shell out the dough for the carb legal parts(headers$400 vs $150 I can make my self with smog tube for emissions but no sticker no pass)

    I'm getting thing prepped for install and cleaned and painted the rims I got at the junkyard and touched up the calipers and painted the parts of the rotor that doesn't touch the pads... I dont even want the tire guy to mount the wheel cause he might scratch the caliper its a close fit on the caliper to rim clearance I can barley stick a finger between em, plus I get pissed when those monkeys tighten the shit outta em with the impact gun. But anyways here's a fresh pic I had I knock the dust of the axle.Tomorrow I install can't wait!bounce



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