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I was on my way to a meeting, pedaling along, when suddenly there was a loud creak. I stopped, visually inspected the bike, manually revolved cranks both ways, and made sure nothing was sticking into any revolving parts like spokes.

I couldn't find anything wrong so I mounted the bike again and started pedaling carefully. Then it made the sound again about 50 meters later. This time, I'm fair sure it was from the bottom bracket area, but of course, you can never know for sure.

I canceled my meeting and currently I'm walking my bike around looking for a LBS that is open this hour. I'm not carrying enough tools to go loose on the BB, chain or cranks.

My bicycle is a 1970s steel Benotto with a Shimano 600 crankset.

Anyone have any idea what this could be? Feel free to ask questions. I won't have anything to do for a while now...

I have tried applying force to various parts of the frame and wheels without being able to trigger the sound, but for all I know I may have missed the important part. So far, I gave only been able to trigger the sound by sitting on my bike and pedaling (both carefully and violently.) I have not heard the sound when just coasting, but on the other hand I have also not spent a significant amount of time coasting since it happened (if we exclude walking with the bike next to me, which I have done quite a bit, by now.)

Seat post is another possibility, but I haven't been able to reproduce the sound when stationary yet, even if I shift my weight around on the saddle.

Edit: new evidence! I sat up and thought I'd try riding a bit toward my destination. After a couple of minutes, the pedals started resisting way more than they should in this gear. Both backwards and forwards. Coasting still no problem.

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    The first easy thing to check is the crank bolts. You may even have the tools with you. If the bolts work loose the cranks don't necessarily give immediately, and they can make quite a noise when they do. – Chris H May 16 '17 at 16:26
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    So long as the cranks are securely attached to the spindle and the pedals securely in the cranks, when a BB fails, its not really that bad; you're just going to not be able to apply power. Also, check chainring bolts. And when you checked the spokes, did you see that there weren't any abnormally un-tensioned (squeezing them to see this)? – Batman May 16 '17 at 16:27
  • Thank you for reassuring me, @Batman. I gained the courage to hop onto the bike and very carefully start riding toward home, but after only a few minutes the pedals started resisting an unnatural amount when turned either direction, but not when coasting (ruling out back wheel). I guess I could remove the back wheel and chain to verify my my BB suspicion and rule out the rear derailleur definitively. – kqr May 16 '17 at 16:59
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    Well, it'd suffice to just remove the rear wheel (the chain on the chainring doesn't do anything, but you could just drop it easily with the rear wheel out). But a rear derailleur can't provide a significant amount of resistance -- it (or the hanger) would likely break if the resistance is caused by it. So, I guess you're due for a new BB. – Batman May 16 '17 at 18:07
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    If you're getting resistance it should be easy to pin it down. – Daniel R Hicks May 16 '17 at 21:27

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