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Thread: Possible to use '83 rear end on '74/6? Easily?

  1. #1

    Possible to use '83 rear end on '74/6? Easily?

    Cause I have '83 R100CS parts bike with what looks like an o.k. rear drive. And looks as if my R90's is leaking more and more.
    Figured if poss. to just swap with out much trouble, then I can address the leaky one at my leisure, and still be riding.

    Guess the axel is probably different size off the top of my head, but haven't had a chance to check. Probably some reason too, that can't just swap out whole rear end, drive shaft, swing arm and diff. I'm betting.

    Any thoughts?

    Thanks guys.


  2. #2
    Liaison 20774's Avatar
    Join Date
    Sep 2005
    San Antonio, TX
    Two things that I wonder about. Does the shock on the final drive attach in exactly the same spot. If not then you're going to have an issue with the other side shock and dimensions. The second thing that will be an issue is the mesh of the splines. They won't match and one or both will take a beating.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Registered User lkchris's Avatar
    Join Date
    Mar 2003
    Albuquerque, NM
    It's not going to be the same gearing.

    The R100 will surely be 2.91-1 and your /6 has something lower. You don't likely have the power to pull this ratio, and bike could feel sluggish.

    Not certain whether a 1977 speedo is compatible, but it's the only year that looks like yours (orange pointer) and only year that style geared for 2.91.

    You'll have to convert the drive for drum brake use, too.
    Kent Christensen
    '12 R1200RT, '02 R1100S, '84 R80G/S

  4. #4

    Thanks guys.

    Sorta as I suspished. Worth a shot. Think I'll just fix the leak and be done with it.


  5. #5
    No longer a member here
    Join Date
    Apr 2006
    Your 83 R100CS also has a rear disc brake. Your R90S has a drum. I went through this possible conversion elsewhere (1978 R100S) and after multiple advice, went against it. Biggest problem is finding a spoke wheel with disc brake.

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