OMG! Drivetrain mystery solved.- Mtbr.com
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  1. #1
    mtbr member
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    OMG! Drivetrain mystery solved.

    Today was maintenance and rebuild day. When pulling the QR from the rear axle there was a lot of resistance. Even after cleaning out there was resistance. So I thought the QR was bent, time to try another. That one was tight too. Then it dawned on me - the axle was bent!

    Yep, it is bent. Roll it on a flat surface and it flops like a defective cue stick. It seems that the most curvature is where the bearing nut sits on the drive side. That's where the cog applies the most force. So chain tension is not just theory - it bends steel. The threads are worn out where the axle hits the hub interior.

    What does this solve? (1) Mysterious change in chain setup from ride to ride. Without changing the sliding drops I would get a tight or looser chain even if the axle were seated perfectly in the drops. (2) When going up a steep slope I could get a sudden twang! so even my riding buddy would say "What's that?". (The chain would then be looser when I looked at it) It had to be the axle rotating between the drops against the binding force of the QR. (pedaling force would tend to rotate the axle so that the bend is forward).

    So it's time for a new axle (and chain and cog and chainring).

  2. #2
    Reviewer/Tester
    Reputation: Rainman's Avatar
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    ..Aha!! nice find.

    R.
    It is inevitable ...

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