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My crank has a little slack and cracks more and more when I pedal, but only on only with the left pedal.

What could be the cause(s) of this ?

Video of the loose crank:

Video of the cracking crank:

  • By "cracks" do you mean "makes a sudden sound", "fractures" or is it a typo for "creaks"? – David Richerby Sep 1 '16 at 8:20
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    I suspect that your "crank" is loose on the crank shaft, if this bike has a 3-piece crank. This can rather quickly destroy the crank, so you need to get it tended to pronto. – Daniel R Hicks Sep 1 '16 at 11:45
  • Thank you Daniel, its louder and louder so I'm afraid you are right – Pleymor Sep 2 '16 at 19:13
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If it is an older 3-piece crank, and if you feel play on the left-side downstroke, then it could certainly be a loose cotter, but it could also be that the bearing cap needs to be tightened in a tad more. I have an older 3-piece crank (w/ loose ballbearings) and I've had to do that before, especially after an overhaul when things tend to loosen up after a few rides.

Of course, there are many types of bottom brackets, as explained here:

https://en.wikipedia.org/wiki/Bottom_bracket

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  • I'll record a video of my problem and then check your hypothesis, so that it can be useful for future diagnosis. Thanks ! – Pleymor Sep 2 '16 at 19:15
  • It was the left crank which was damaged with time, and needs to be changed because it is very loose and can't be tightened anymore (30yo bike) – Pleymor Sep 3 '16 at 8:59
  • @Pleymor - If the crank had been tightened when the symptoms first appeared, it likely could have been saved. – Daniel R Hicks Sep 3 '16 at 11:43

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