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Old 09-06-08, 02:20 PM   #1
daroga
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Help pinning down a clunk on wife's bike?

Hi all!

I need a hand here, for things to check on my wife's bike. We just recently bought her a Trek 3700 (woman's). It's been working wonderfully, except recently it's started to make this steady clunking noise when it's being ridden. If you're the rider, you can feel it in the seat on your butt.

A couple of facts about it:
- It happens steadily, whether you're pedaling or not (something to do with the wheel I'd have to imagine, right?)
- It does not happen unless a person's weight is applied to the seat (free spinning the front wheel or pedaling the back without anyone on it produces nothing)
- I'm somewhat (read: very) ignorant, but it doesn't appear to be the chain being loose, as it seems as taut as the chain on my Trek which doesn't have them problem.

Watching the bike as she rides it, I can't see anything hitting the frame anywhere. Brakes are well aligned, chain is situated in place well, etc. But if someone has something specifically for me to look at, that would help a lot.

Thanks!
Tim
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Old 09-06-08, 02:25 PM   #2
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I've got a unicycle making funny noises that I haven't figured out, myself.

Two somewhat unlikely possibilities: A bulging spot on a tire; or a speedometer magnet hitting.
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Old 09-06-08, 02:50 PM   #3
daroga
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I'll have to check the tire thing. I don't think it's over or under inflated, but it's a possibility. And there's no speedometer on her bike.

Sadly, we just moved, and the closest real bike shop is like 100 miles away to have someone knowledgeable check it out.
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Old 09-06-08, 02:55 PM   #4
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Can you hear the noise or just feel it? If you can only feel it, then I'd say the seat has a broken seatpan or rail or seat post. Any of these things are potentially dangerous so you need to be sure that none of these things are broken.

If you can hear it as well as feel it, then it could still be the seat. But I'd say to look at the seat bag (if you have one) for it swinging and hitting the seat or seatpost. Check the contents of the bag too, sometimes wrenches will knock together and make all kinds of strange noises. (look at the tail light/rear reflector too if you have one for the same reasons)

Check the water bottle cages. I had a "squeek" that was driving me nuts last week. Turns out the seatpost water bottle cage was loose and moving when a full bottle was in place.

Check that the pump mount is securely holding the pump and that it isn't being hit by a crank arm/foot as you pedal.

Check the bottom bracket (crank "axle") for properly tightened cups. Check that the crank arms are tight.

Check the skewers are tight. If they are loose the wheel will shift in the frame dropouts and could make a noise and "bump" that you might feel.

Turn the bike upside down and carefully check ALL the frame tubes for cracks or long chips in the paint. Do the same when the bike is upright too. Cracked paint usually means the tube is cracked. (but not always)

My guess is that, because the noise only happens under rider weight in the saddle AND because you can feel it, the saddle is broken but DO NOT rule out the other possibilities.

Good luck and let us know what you find out.
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Old 09-06-08, 03:05 PM   #5
daroga
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Rob,

Thanks for that. I'll have to do some Googling to know what all the pieces are you were talking about, but I'll check to make sure everything's tight.

If we pop the seat and its pole out, what am I looking for that might be broken? It doesn't have a bag on it at all, and it makes the noise just when it's in motion, regardless of terrain (smooth, bumpy, etc.).
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Old 09-06-08, 03:38 PM   #6
Mr. Beanz
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I had a strange noise (actual clunk) in my bike. Had good components and fairly new so I was baffled. Turns out the lockring on the cassette was a bit loose. I tightened it, voila! No more noise!
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Old 09-06-08, 04:18 PM   #7
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My mtb was making a clunking noise and I could feel it too. I was already dreading the thought of having to take it to the LBS but first I changed out the pedals. That did the trick! Now I'm silent but deadly again! I plan to go clipless real soon anyway.
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Old 09-06-08, 04:37 PM   #8
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Yeah, it's definitely not the pedals because the noise happens when in motion, even without pedaling.

I'm thinking we might just have to bite the bullet and take it into the bike shop 2 hours away. Lame.
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