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Every time the right pedal goes over the top I get a single clack noise with a little more 'travel', a point where the bottom bracket moves without any resistance, from that point in the rotation. I have only just noticed it recently and it seems to be more noticeable on the lower gears where the cogs are smaller.

Any thoughts on what to do or what might be causing the problem?

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Check the simple stuff too. I recently had the exact same problem with my new bike - a clack every revolution when in the small ring (same pedal position as you too!) - and it turned out to be the front derailleur cable end hitting the crank arm. Just bend the cable away from the crank. –  Joe Bronikowski Sep 9 '12 at 12:23
    
Pictures of the bike, especially the bottom bracket may help us figure out the more likely possibilities. –  Colin Newell Sep 10 '12 at 5:50
    
Ooops, first off that should be the larger cogs that the clacking is more noticeable on, sorry. –  user1170304 Sep 10 '12 at 9:29
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3 Answers 3

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The first thing to do is to tighten the cranks -- on both sides. If the problem is a loose crank (which you may not detect by simply shaking the crank), then riding with it loose will destroy the crank in short order.

After that, my next suspicion would be a loose bottom bracket cartridge.

But even a bad pedal bearing can produce similar symptoms.

(And Joe's suggestion to check for something physically hitting something else is a good one.)

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I had something similar on a bike wheel, it clacked, sometimes wiggling slightly, once per revolution, in that case it was a bearing (in the years before sealed bearings came along). –  William B Swift Sep 9 '12 at 15:52
    
It is the bottom bracket. I shook it and it's pretty loose, seems to be making the noise. Is it bad to ride on it? I don't have the tools at home and have had to ride it in to do it at the local bike workshop. –  user1170304 Sep 11 '12 at 8:39
    
If it's the entire crank axle that's loose then it's safe to ride, within reason. If it's a loose crank arm -- one arm moves relative to the other -- then you should avoid riding it if at all possible. But the latter can be temporarily fixed with just the right size (8mm) allen wrench. –  Daniel R Hicks Sep 11 '12 at 11:10
    
Very helpful, thanks! –  user1170304 Sep 12 '12 at 21:23
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It's always difficult to diagnose noise descriptions, especially in the drivetrain. But guessing by the:

... the bottom bracket moves without any resistance ... more noticeable on the lower gears ...

I would say the rear hub's freehub is damaged. Pop it off the hub body and inspect where the pawls are (mind the pawl springs don't ping out!), look for broken pawls and/or mashed ratchet teeth (the teeth which the pawls engage with). Post some pictures of it if you are unsure.

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Were you gonna volunteer to help the OP put his hub back together? –  Daniel R Hicks Sep 9 '12 at 13:59
    
I'm quite sure he/she's capable of dismantling something with few parts and putting it back together again. At the very least, be able to type the make and model into Google and read a service manual. How else would you learn to service it? –  cmannett85 Sep 9 '12 at 16:58
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I've had this kind of noise and spent hours trying to find it. Changed the pedals, changed the bottom bracket, fiddled with the headset/stem etc. Eventually decided to put spare wheels on.Changed the rear, still there, changed the front - silence :) Put best front wheel back on and still silent.

To get my bike into the car without putting the seats down I have to take the front wheel off. I've had this kind of click since and loosening the front quick release reseating the wheel and tightening it again always fixes the problem.

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