R75/7- driveshaft bolt stripped!! why?

Discussion in 'Old's Cool' started by herman maire, Sep 6, 2011.

  1. herman maire

    herman maire Been here awhile

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    Thanks for looking. I am trying to figure out why the bolt stripped on my driveshaft coupling when I tried to torque it to spec (170-180ft/lbs.)

    Is this the correct torque figure?

    This was supposed to be a 2 minute job.... all I had to do was torque the coupling bolt on the driveshaft and install my shinny freshly painted swing arm :clap.

    It was not to be, it went from worse to worse.....

    After the bolt stripped, it was impossible to remove the nut since all it would do is spin and would not catch the last 2 treads on the driveshaft.

    I bring it to a machine shop, I tell them the problem, they say no problem. I say cool.

    While I am busy working on something else I get back to the shop and they hand me the shaft in 2 pieces.... I say WTF did you do.

    Oh, we had to torch the nut off also cutting the treaded section of the driveshaft off. Its amazing how stupid people are.

    So, if anybody has a driveshaft that would work with a R75/7.... please PM info and price.

    Thanks
    #1
  2. jbcaddy

    jbcaddy Long timer

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    :huh that is a sad tale:cry so sorry
    #2
  3. pommie john

    pommie john Long timer

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    I haven't got my manual in front of me, but 170 ft pounds seems a hell of a lot.
    #3
  4. pommie john

    pommie john Long timer

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    As you were! My manual says that's the right torque.
    #4
  5. airheadDavey

    airheadDavey Adventurer

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    There is now way they are 170ftlbs. I think you may have misread the manual. The center nut on the back of the output shaft I believe is that tq spec. I dont have the manual in front of me to give you the proper specs on the bolts. Sorry that happened to you and I feel your pain.

    [​IMG]
    #5
  6. airheadDavey

    airheadDavey Adventurer

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    Are you sure its not 170 inch pounds?
    #6
  7. noman

    noman Long timer

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    from my r75/6 bmw repair manual:

    hex nut on coupling bell housng 173.5 -188 ft-lbs
    twelve-sided bolt 17.3 - 18.8ft-lbs

    may not be the same as r75/7
    #7
  8. herman maire

    herman maire Been here awhile

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    #8
  9. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Folks, I think he's talking about Nut #7 that holds on Flange #6.

    [​IMG]

    I don't have the /7 spec with me, but 170 ft-lbs sounds correct-ish.
    #9
  10. herman maire

    herman maire Been here awhile

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    Bill,

    Thanks for that.... yes it is indeed #7.
    #10
  11. wirewrkr

    wirewrkr the thread-killer

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    Just bad luck, that's all.
    Move forward, get another shaft and fix it.
    Most used shafts have notchiness in the joint.
    It's just the way it is, don't freak out when you find a used one that way.
    Some is okay, Too much is not.
    #11
  12. Dolly Sod

    Dolly Sod I want to do right, but not right now

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    Did you torque it with dry or oiled threads?
    #12
  13. PaulRS

    PaulRS Dutch fool

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    For the /7 the manual states a slightly lower spec, around 150 Lb-Ft (converted from Nm).
    But that wouldn't strip the threads, imho.

    Manual says nothing about oiling, so it should go on dry.

    Just bad luck, I think.

    Paul.
    #13
  14. bmwrench

    bmwrench Long timer

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    The spec is/was 170 lbs/ft, but I haven't put that much torque on one in years. Go to 150 with a drop of red Loctite on the threads.
    #14
  15. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    And the coupling is a taper-fit so make for absolutely certain that BOTH parts of the taper (inner & outer) are oil-free-- clean with acetone or brake cleaner if need-be.
    #15
  16. disston

    disston ShadeTreeExpert

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    I believe it's that much. When I took one off to remove shaft it was that tight. The bell was really tight and we had some trouble with getting the bell off, using a press. The guy that was helping me said to not put it back that tight. 150 should be plenty.

    I would not use red locktight here. You may not be the one to some day take it apart. Clean and dry.
    #16