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What does it take to put an 8.5 into a 7.5 car?

Discussion in 'General Discussion' started by MrSony, Oct 11, 2017.

  1. MrSony

    MrSony Comic Book Super Hero

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    Is it literally a drop in swap? Do I need a shorter driveshaft, or is that only when going to a 200r4? What codes on the rear should I look for? Asking for a friend... ;);)
     
  2. Injectedcutty

    Injectedcutty Royal Smart Person

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    Unbolt the 7.5, unhook brake line, remove. Bolt in 8.5 and reattach brake line.
    Shorten driveshaft by 1 inch and rebalance.
    Th350 and 200-4R are the same length.
    Check fluids, and do burnouts :cool:!!!
     
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  3. -83MONTESS-

    -83MONTESS- Moderator
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    Mine required a 1" shorter driveshaft but I have heard others say 1.5" depending on car. Doesnt make sense to me but whatever
     
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  4. MrSony

    MrSony Comic Book Super Hero

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    :D
     
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  5. MrSony

    MrSony Comic Book Super Hero

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    I doubt the DS would care about that extra half inch. Unlike some girls I used to know....
     
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  6. Injectedcutty

    Injectedcutty Royal Smart Person

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    :rofl:
     
  7. 64nailhead

    64nailhead Master Mechanic

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    The driveshaft length is affected by several variables - yoke on rear, suspension height, trans/engine angle, transmission model,etc. I do agree that it should be relatively standard, but if you're swapping the rear or transmission that is going to result in a driveshaft length change, then that is the time to optimize the length rather than dropping off an inch and 'calling it good' IMHO.

    It's also a great time to upgrade to a heavier shaft (tube) and u-joints if you're making alot of power, or plan to in the future.
     
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  8. lilbowtie

    lilbowtie Royal Smart Person

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    I'll get on my soap box again and ask you to take a look at "drive shaft critical rpm". Depending on the rpm range your planning on running it can have devastating results. Google - drive shaft critical rpm, Precision Shaft Technologies has a nice chart.

    IMG_4130.JPG
    IMG_4133.JPG
     
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  9. foxtrot

    foxtrot Royal Smart Person

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    Holly cow, that's gruesome! Hopefully nobody was injured with that carnage.

    Definitely a good tip to take to heart.

     
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  10. olds307 and 403

    olds307 and 403 Royal Smart Person

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    Another reason to use the factory, shorter heavier duty 8.5" drive shaft if you can get it with the rear.
     
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