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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 07-23-09, 08:50 PM   #1
arexjay
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I know it's hard to diagnose bottom bracket noise, buuuut...

I know it's hard to diagnose bottom bracket noise (or any bike noise) through the internet, buuuuuuut this is killing me! It's a carbon bike - Trek Madone 4.5, Shimano 105 cranks/bottom bracket. I'm building it up at work. The head mechanic was gone today, the other two guys I work with couldn't figure it out either.

The sound is directly proportional to the rotation of the crank. It's not a clicking or pinging or anything. More of a vibration/rubbing (not chain rub, deeper), and it most noticeable by feel than by sound - feels kind of like a hub that's too tight, almost like it's seizing. It's 'bumpy' when riding and turning the cranks, and you can feel it through the downtube when it's in the stand. It only happens three times per full crank rotation, in the same three spots. The bottom bracket cups/bearings are tight, nothing is loose. As far as I know, nothing is stripped. The rear derailleur cable tension and limit screws are set correctly, and it shifts perfectly in both the back and front. The cassette is tight.


ARGH!!!
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Old 07-23-09, 09:40 PM   #2
Panthers007
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Put it together backwards? It happens. Did you use carbon-prep grease? Did you remember to tell the head-wrench how cute he's looking - tomorrow?
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Old 07-23-09, 10:20 PM   #3
stausty
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So this is a cup-and-spindle bottom bracket, cartridge, or external? What positions does it make the noise?

Maybe you've got one ball in there that's the wrong size. Or cross-threaded a cup. Or it's external and the BB needs to get faced. Or the spindle is bent.
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