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I have over-tightened the bolt on the rear derailleur clamp (Shimano tourney). There is no resistance on the bolt, when tightening it or untightening but the clamp does not move anymore. I don't want to force something the wrong way anymore. How can it be unblocked now?

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    You likely stripped the threads. You may try going to a bike shop, car garage, or machine shop to get the threads repaired, but it may be cheaper just to get a new derailleur.
    – MaplePanda
    Commented Feb 17, 2021 at 20:05
  • MaplePanda the bolt nut does screw and unscrew without problem. It's the clamp piece which does not move. Does it have threads?
    – Learning is a mess
    Commented Feb 17, 2021 at 20:38
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    No the wee clamp plate does not have threads. It is a close slip-fit on the threads of the bolt. Could be the clamp plate is cocked at an angle, and the bolt has dug into the sides? Some gentle twisting with pliers should get it to move.
    – Criggie ♦
    Commented Feb 17, 2021 at 20:52

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I would back off the bolt in a manner similar to your second image. With a small screw driver pry the clamp away from the derailleur toward the head of the bolt. When the clamp is free, you will notice a small "nub" protruding from the derailleur. The purpose of this nub is to prevent the clamp from rotating when it is tightened. My guess is your clamp is on the "nub". This is preventing the clamp from seating against the derailleur and holding the cable in position.

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    When prying, use the thinnest blade available, one that will fit in the narrow gap on the right-hand side of the bolt, as seen in the image.
    – Daniel R Hicks
    Commented Feb 17, 2021 at 23:04
  • It did work, thanks.
    – Learning is a mess
    Commented Feb 18, 2021 at 15:34
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Grip the clamping plate edges top and bottom with vise-grips, water pump pliers or the like and wriggle it. It may even come loose if the bolt is entirely removed.

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