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Discussion Starter · #1 ·
Sorry for the technical term but as I pedal there seems to be a mild "clunking" sensation coming from some part of the drive train. This generally happens on the flats with a fairly high (but still reasonable) cadence. It happens in my higher gears. My first thought is that my chain is a bit too long. I'm using an FSA compact crank with 12-25 in the rear. Any thoughts???
 

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When your bike makes the noise do you notice any slipping in the drive train. If so it may be your rear hub. Thats something that just happened to me. My spring that forces the pawls out inside the hub has gotten weak and I experience slippage and a clicking sound at various times as I pedal.:mad2:
 

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Can you be more specific?

Is the clunk random? Once per revolution? Twice/rev? In the saddle or out? Does it happen in more than one gear or does it happen in different gears? Can you feel it in your hands or feet? Can you hear it?

You get the idea.

Dave
 

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Discussion Starter · #9 ·
David Kirk said:
Can you be more specific?

Is the clunk random? Once per revolution? Twice/rev? In the saddle or out? Does it happen in more than one gear or does it happen in different gears? Can you feel it in your hands or feet? Can you hear it?

You get the idea.

Dave
Here ya go, Dave:
When it happens (i.e., it's not constant) it happens once per revolution, while I'm in the saddle, generally at a moderately high cadence on the flats. It happens in different gears (I notice it in the middle to higher cogs) and I seem to notice it in the big ring (50t - I have a compact dbl). I feel it in my feet and can hear it. This is a test of my wordsmith ability but there might be a sublte "looseness" right before the "clunk". FWIW, I've grabbed the individual cranks to check if they are loose and, nope, they are quite solid.
 

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I feel it in my feet and can hear it. This is a test of my wordsmith ability but there might be a sublte "looseness" right before the "clunk".
Here's what I think: at one point in the crank revolution, you're slowing down your foot speed for a fraction of a second. Instantly, the bike freewheels and the upper run of the chain goes slack. When you speed your foot back up again, you snap the chain tight, slamming the freehub pawls into the locked position. This will make a definite clunk.

See if you can duplicate the clunk with the rear wheel off the ground and turning the cranks by hand. Slow your hand speed down for a fraction of a second, then speed up again. If you get the exact same clunk, chances are your on-the-road clunk is the sound of your less-than-perfect pedaling style.
 

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Do you have a cadence or speed sensor mounted on the rear chain stay? I had "clunk" too -- found out it was the cadence magnet on the crank hitting the receiver mounted on the chainstay. Only happened when I was pedaling under certain circumstances.
 

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KarlW said:
Here ya go, Dave:
When it happens (i.e., it's not constant) it happens once per revolution, while I'm in the saddle, generally at a moderately high cadence on the flats...
Crank is hitting the kickstand?

:p I always wanted to say that.
 

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KarlW said:
Here ya go, Dave:
When it happens (i.e., it's not constant) it happens once per revolution, while I'm in the saddle, generally at a moderately high cadence on the flats. It happens in different gears (I notice it in the middle to higher cogs) and I seem to notice it in the big ring (50t - I have a compact dbl). I feel it in my feet and can hear it. This is a test of my wordsmith ability but there might be a sublte "looseness" right before the "clunk". FWIW, I've grabbed the individual cranks to check if they are loose and, nope, they are quite solid.
Coool.

Are you saying that it doesn't do it if you are out of the saddle? If that's the case then it points the the saddle/seatpost. This is pretty common. Grease the post (not a carbon post), a light coating of grease on the saddle rails where the rails get clamped by the post.

What saddle and post are you using?

Dave
 

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Discussion Starter · #15 ·
Sigh...

wim said:
Here's what I think: at one point in the crank revolution, you're slowing down your foot speed for a fraction of a second. Instantly, the bike freewheels and the upper run of the chain goes slack. When you speed your foot back up again, you snap the chain tight, slamming the freehub pawls into the locked position. This will make a definite clunk.

See if you can duplicate the clunk with the rear wheel off the ground and turning the cranks by hand. Slow your hand speed down for a fraction of a second, then speed up again. If you get the exact same clunk, chances are your on-the-road clunk is the sound of your less-than-perfect pedaling style.
While there may still be mechanical explanations for the "clunk", I suspect Wim has identified the problem...as hard as it may be for me to believe, it appears my pedaling style could use some improvement. I noticed this morning that I get the "clunk" even when standing (contrary to my previous post). I was just doing a leasurely standing climb and rolling over the cranks with a bit of an erratic cadence and "clunk" goes the drive train. I did not notice this when I was spinning a consistent cadence later on. Of course, there may still be a mechanical problem but this explanation feels on.

David: I have a Fizik saddle and Ritchey carbon post but the "clunk" is definately felt in my feet/pedals.
 
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