Rear Ends - 9 Inch, 10 bolt, 12 bolt...What's The difference?

Discussion in 'Transmission & Driveline Topics' started by MarcZ, Jul 27, 2007.

  1. MarcZ

    MarcZ Veteran Member

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    Dec 6, 2006
    San Diego, CA
    Well, I am planning out how I want to build my car, I'm not an excessive planner or anything but I think it's important to have a thought out plan for something like this.

    One thing I cannot correctly plan is rear ends, being I just don't understand the difference between them so I'm not sure which one I want. Whats the difference in the different rear ends? Different characteristics and uses? Can you name them, please?
     
  2. tom3

    tom3 Veteran Member

    10,480
    26
    Aug 1, 1999
    ohio
    Mainly strength. The bigger the gears the stronger the rear end. The "bolt" designation is just a way to indentify the rear end. A 10 bolt is not as strong as a 12 bolt. The bolts are what holds the ring gear to the carrier, but also the cover to the housing so you can see what the size is without removing the cover. The Ford design 9 inch is a whole different animal, and a good one.
     
  3. MarcZ

    MarcZ Veteran Member

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    Dec 6, 2006
    San Diego, CA
    Cool, because I've seen the 9 inch ones go for cheaper. Thanks for the info.
     
  4. andrew1977

    andrew1977 Veteran Member

    1,501
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    Oct 1, 2006
    parksvegas, BC
    get a 8.5" 10 bolt.... people will tell you they arent strong enuf but they can handle a sh!t load of abuse... my dad had his stock 8.5 in his camaro and blew up two t-10 4 speeds.... the rear end didnt complain once.

    if you have an 8.2" 10 bolt junk it.... its useless basicaly. there are two diffrent 8.5" ten bolts... there is 273 and numerically higher 8.5" which has the thinner style carrier, and then there is the 256 which has the thicker carrier. the 256 gear does need a ring gear spacer though if you want to get say 373's. i personally belive the 256 is much strounger then the 273 and numericaly higher because theres is alot more metal.

    i have a 256 posi but im putting 373 gears in soon. the only thing im concerned about with the 256 is that when i put 373s and the ring gear spacer on the bolts will be longer and might be able to flex and lossen off when the the gears heat up and cool down. but thats just what i think might happen.

    a stock 8.5"ten bolt will handle over 400hp with a standard. with a auto it will might handle around 500hp without blowing up. iv got picks of a 2nd gen doing wheelies with an 8.5" ten bolt.

    a 10-bolt is almost as strong as a 12-bolt since its ring-gear diameter is only 0.375 inch smaller than a 12-bolt...

    hope everything i wrote makes sence.... long hard day of work and im very tired..... pm me if you have any more questions about ten bolts...
     
    Last edited: Jul 27, 2007
  5. wookie

    wookie Veteran Member Lifetime Gold Member

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    Jul 12, 2006
    Daytona Florida
    The other factor is the way the axles are held in. GM uses a "C" clip to retain the axle. Ford does not. The "C" clip can fail and usually does over 400+hp. When it does, the axle simply slides out of the rear end housing and takes off, taking the wheel and tire with it. There is a ford-style C-clip eliminator setup you can install. A must have if you put in a mini spool, full spool, or even a posi.
     
  6. wookie

    wookie Veteran Member Lifetime Gold Member

    3,049
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    Jul 12, 2006
    Daytona Florida
    Also, GM made 3 different rear ends in the 10 bolt style. 8.5 inch up through about 1981, then down to a 7.5 inch through the mid 90's, then back up to 7 5/8 I believe from then out. The early 8.5 is the strongest IIRC, but the new ones came with disks on some applications, and can be upgraded in some cases. Stronger axles are determined by the number of splines on them. You have no doubt head of 28 spline, (Stock GM) up through 33 or even 35 spline axles. The more splines, generally the stronger it is.
     
  7. K5JMP

    K5JMP Veteran Member Lifetime Gold Member

    I have been running a 9" unit with 33 spline axles, .390's and a Detroit locker for over 12 yrs now... same unit. No issues what so ever with the diff....
    I abuse the hell outta this setup... the rear has been the only truly bullet-proof piece in the car. I have twisted driveshafts... broken windshields and T-tops... even a tear in the sheetmetal at the top-rear of the drivers side window... and the 9" rear diff just keeps rockin' on.:cool:
    I keep killing ST-10's.. LOL! Looking for a TKO next time around:)

    Oh yeah... the difference... I haven't been able to kill the 9" unit
     
    Last edited: Jul 27, 2007
  8. night rider

    night rider Veteran Member

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    Aug 6, 2002
    Bremen, Ga
    Wookie.. The 7.625" (7-5/8") started in 1986

    71-81.... 8.5"
    82-85.... 7.5" (26 spline axles)
    86-mid 91... 7.625" 26 spline
    mid 91 to 02... 7.625" 28 spline
     
  9. big gear head

    big gear head Veteran Member

    5,822
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    Jul 30, 2001
    Central City, Ky.
    First you need to know what you want to do with the car and what you expect the rear end to handle. We can not recommend a rear end without knowing what your intentions are. The 9 inch should be considered a high end performance rear end and a lot of overkill for most street/strip cars. The 8.5 10 bolt and the 12 bolt Chevy are more than strong enough to handle most street/strip use, and they are lighter and use less power to turn. The differential that you choose will depend on what type of driving you want to do. If this will be a street/strip car then a good cluth type posi like the Eaton would be a good choice. If you will be doing auto cross events and road racing then a Truetrac or Torsen would be a better choice. If it will see more drag strip use than anything enlse then a Detroit Locker would be better. The same thing goes for the gear ratio and all other parts of the rear end. You need to know what you want it to do before you can pick the parts for it.
     
  10. MarcZ

    MarcZ Veteran Member

    385
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    Dec 6, 2006
    San Diego, CA
    Well I want to have just a tad over 400 HP to the wheels on a 4 speed manual. Mostly street use, but occasional autocrossing or roadracing is a strong possibility.
     

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