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my left pedal keeps falling off, I think it's loose, or I'm not tightening it properly, but every time I ride my bicycle it gets loose

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    Welcome to Bicycles Stack Exchange. Some more information will help us with you problem. Please edit your question to add the make and model of bicycle. Adding a pictures of the pedal and crank threads will also help (You have an upvote so you should be able to add pictures. If not, provide links and someone will edit your question for you.) – Argenti Apparatus Apr 17 '18 at 16:22
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    If this bike has been ridden with a loose pedal for a long time, then it could have damaged the threads on the pedal or inside the crank arm. Loctite/threadlocker may help if its not too far gone. – Criggie Apr 17 '18 at 22:44
  • Do note that the left side pedal is reverse-threadded, so you "tighten" it to loosen it. – Criggie Apr 17 '18 at 22:45
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    Note that if the bearings are bad in the pedal itself then this will cause the pedal to unscrew from the crank arm. If the pedal doesn't spin freely either rebuild the bearings in it or get a new pedal. – Daniel R Hicks Apr 17 '18 at 23:40
  • Not even a long time, in my experience. The left crank arm is toast. – whatsisname Apr 18 '18 at 23:06
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There’s a best case scenario and a worst case scenario. Neither is too terrible.

Best case scenario: Your pedal is just loose. You can tighten it with a pedal wrench (some pedals can use a hex wrench) — however note that the left pedal is left-hand threaded so it’ll be the reverse of what you are used to. Thus, you have to screw it counter-clockwise to tighten it.

Worst case scenario: is that the crank threads themselves are badly damaged. This can happen if you pedaled on it while it was loose — because the crank is usually soft aluminum and the pedal is hardened steel. If the crank threads are worn, then no amount of tightening will work. Instead, you’ll have to take the pedal to your local bike shop where they will drill out the threads, tap slightly larger ones, and insert a helicoil. This will allow your pedal to go back on. It shouldn’t be too expensive, usually one-half hour of shop labor plus the cost of the helicoil (5-10 eurodollars).

So neither scenario is too terrible. Good luck!

P.s. don’t ever use thread lock to try to retain a loose pedal. Pedals by design are always tightening themselves when pedaled normally. If a pedal is loosening itself, it’s not because of screw loosening forces, it’s because the crank threads are bad, and threadlock will not help. However, if the threads are still good then threadlock can cause the pedal to bind terribly such that the pedal won’t ever come off. Instead, you should grease the threads of pedals rather than ever use threadlock.

  • Pedals will UNTIGHTEN when riding. It is a safety measure, meaning that if the pedal bearing locks while you're riding it doesn't lock any further. In the other case it will just snap your ankle and throw you over the bars. So if a pedal is loose when you start your ride it will loosen further en route thus the need for a correct tightening torque from the beginning. – Carel Apr 18 '18 at 15:47
  • That’s an urban myth @Carel - see the Sheldon Brown link I put in. – RoboKaren Apr 18 '18 at 15:50
  • Have you ever experienced that? – Carel Apr 18 '18 at 15:51
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    Experienced what? That you posted less than 1 minute after I posted the link seems to suggest you didn’t bother reading why Sheldon Brown would think you were wrong. – RoboKaren Apr 18 '18 at 15:53
  • No, that loose pedals on left and right sides come off when you hold the pedal axle between your fingers and pedal with the rear wheel lifted from the ground. (BTW: I know that article by Sheldon and he doesn't mention the bearing lock. Imagine the locking bearing and what would happen to the left pedal. It's OK for the right side that one will be safe.) – Carel Apr 18 '18 at 16:03

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