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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 02-01-12, 10:07 PM   #1
cyclisteaux
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Grinding on left side when off the saddle? Please help!

I have a 2011 Cervelo P4 with a Zipp VumaChrono crankset and Dura Ace Di2. When I stand to climb hills, and power down on the left pedal, a grating and grinding noise emits near the crankset. Sounds like metal on metal, but not sure. I've taken it to my mechanic for a tuneup but he didn't fix it.

When I brought it back, I told him to test it on a hill but he responded there are no hills near the shop! Is there a way to simulate a hill? Shouldn't my mechanic know how to do this???

Any tips would be appreciated.
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Old 02-01-12, 10:56 PM   #2
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is the bottom bracket/spindle, cups and bearings adjusted properly and complete? Does the left pedal have sticky spots indicating a bad bearing or bearings too tight?
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Old 02-01-12, 11:13 PM   #3
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Not sure about BB/spindle. I'm not mechanically inclined. Shouldn't my mechanic know all this stuff? I don't think it has anything to do with the pedal, though. Could it be the wheel scraping against the frame somehow? I'm running Zipp 101s.
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Old 02-01-12, 11:25 PM   #4
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Your mechanic isn't thinking, or doesn't want to think. It's easy enough to simulate the load of climbing a hill. All he needs to do is ride hard while gently dragging a brake so it's about as hard as climbing.

Without knowing anything of the general condition of your bike, it could be as simple as the frame, or crank deflecting enough under load for the chain to touch the FD. That has a pretty characteristic sound and should be easy enough to eliminate by ear alone, but it's a place to start.
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Old 02-02-12, 09:44 AM   #5
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FBinNY: Brilliant suggestion, dragging the brakes to simulate hill climbing! Thanks. I'll forward your advice but refrain from calling him a doofus! ;-)
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Old 02-02-12, 09:59 AM   #6
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Originally Posted by cyclisteaux View Post
FBinNY: Brilliant suggestion, dragging the brakes to simulate hill climbing! Thanks. I'll forward your advice but refrain from calling him a doofus! ;-)
As I hinted, I'm not sure he couldn't think of it as much as he didn't want to bother. Before going back, take some time to simulate it yourself using the brakes. Given the nature of the problem, I suspect that it's somehow related to a deflection under load rahter than bad bearings. Try to get to where you can duplicate it consistently, then maybe rather than having the mechanic ride it, you might have him go outside while you ride by and produce the problem in front of him.
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Old 02-02-12, 10:39 AM   #7
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Would be good for you to learn a tiny bit about mechanic because is not that much of help to tell the guy, "it sounds like this" sometimes. Sometimes is so easy as move the crankset laterally, makes sense that the crankset was not designed to move laterally, so if you have a play something is clearly wrong.

Between you and me my 1st suspect is the chain or the chainwheel hitting the fd cage. If that's the case the BB might be lose or something, easy to figure it out just try to move the cranks laterally.
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