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Discussion Starter · #1 ·
and damn good ones I might add, cannot solve this.

Weird feeling/noise: Once every twenty miles or so (rank guess) my drivetrain will CLUNK forward, in a way that feels similar to a cog with a bad tooth, or like the chain is skipping and recatching, if that makes sense. It's a noise and a vibration that I can feel through my feet. I real a brief loss of drivetrain function. Not all the time, once a ride.

Over the course of a year, I and the aforementioned three best mechanics in Kentucky have attacked the problem unsuccessfully. The chain has been replaced. The cassette has been replaced. The shifter has been replaced (unrelated, but still, I want to show that every damn thing has been replaced.)

These are new-last-year Ultegra/Open Pro wheels. Am I down to a freehub body problem? Or -- long shot -- is it possibly something to do with the BB? Oddly, the clunking noise sounds a lot like a BB sounds when it's loose and you squeeze the crankarm to the seat tube to check for movement. But I can't recreate the sound that way, and since I installed the BB myself, I know it's torqued to spec.
 

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passive/aggressive
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sounds bottom bracket-ish to me too or pedal spindle, maybe a foreign body in there that every so often gets onto a bearing track. Also maybe check for broken frame issues, perhaps separated CF seatstay or chainstay?
 

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Number 2 on the course.
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I am thinking the freehub is the source as well, but I would assume that a different wheel was tried at some point in the diagnostic process(?)

I wouldn't be surprised to see this problem replicated near the freehub's transition from freewheeling to engagement. If you are pedaling at just the right combination of speed and cadence you can sometimes produce inconsistent engagement.

If this is the issue, you'd be more likely to encounter it on rolling terrain or any other type of riding where there is a frequent mix of coasting and pedaling.
 

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No Crybabies
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spare wheel?

Henry Chinaski said:
Could be. Could also be the chain trying to move up or down one of the shift ramps on the rear cogs if you've just back pedaled a bit or coasted over rough pavement and starting to pedal forward again.
Seems like the most logical thing to try at this point is another rear wheel.
 

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Impulse Athletic Coaching
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My first guess is a loose cassette, or the wrong spacers in it. Second guess is a tight or loose link in the chain. Third guess is the freehub/bearings being shot in the rear wheel.

The first two can be replicated, the third cannot. Replace the rear wheel and see if it is fixed. If not, it's the chain or BB.
 

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Captain Obvious
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trying a new wheel saved me from replacing a bottom bracket on my wife's mtn. bike.
 

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I weigh-in that it is probably the freehub.

No way it's the BB, that would not cause a skipping forward sensation. Tight links would show themselves a lot more often.

Try the spare wheel, if you don't have one then a new freehub is only in the $35 range so that's not too bad to just see, and then you have a spare.
Tools needed to replace the freehub are chain whip, cassette lock-ring tool, cone wrenches, 10mm allen wrench.
 

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Impulse Athletic Coaching
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nepbug said:
I weigh-in that it is probably the freehub.

No way it's the BB, that would not cause a skipping forward sensation. Tight links would show themselves a lot more often.

Try the spare wheel, if you don't have one then a new freehub is only in the $35 range so that's not too bad to just see, and then you have a spare.
Tools needed to replace the freehub are chain whip, cassette lock-ring tool, cone wrenches, 10mm allen wrench.
Actual BB, no. I kind of meant BB area, such as a loose one that clunks as the bike is rocked under power.
 

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Shirtcocker
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tomk96 said:
trying a new wheel saved me from replacing a bottom bracket on my wife's mtn. bike.
yup...if that isn't it then it's likely the BB
 

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I think i have the same problem !!

JRA, maybe coast a little, start to pedal and clunk snap, feel it come through the crank arm and through my feet. Does not matter if it is big ring or small or what gear I am in. Very random.

I just swapped out the rear wheel and cassette to see if that(freehub) is the problem. I too have swapped out a bunch of parts to no avail, some were just shifted to other bikes like a chain and cassette of same vintage to a second set of wheels.

Now the kicker; I got really sick about 10 days ago, missed alot of work and now am playing catch up, no time to ride.
 

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sounds like a problem i was having

and it turned out to be my freehub body - but on a set of velomax circuit wheels. I had just worn the old freehub body out. Not sure of the innards of an ultegra freehub, but would be surprised that it only last a year, yet I am sure stranger things have happened.
 

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The same thing happens to me - albeit much less frequently - with two wheels, usually when I'm starting from traffic lights.

One has a Dura-Ace 7400 freehub (1991), and the other has an XTR M-900 freehub (1992). It's definitely the bodies, but it only happens very rarely with mine so I just put it with it as the parts are expensive and hard to come by now that they're so far out of production.

Anyway, I'd try to borrow another wheel and see if your problem stops. I'm betting it will.

If it does, you could try servicing the freehub body - if you can find the now-unavailable Shimano tools needed to dismantle it, or a Morningstar Freehub Buddy which fits. It's not complicated to do, but tedious and fiddly, and likely to cost more in labour than a new body will. Also, note that the only way to get internal parts for freehub bodies is by salvaging them.

So, if I was you, I'd try to get the shop to run it past the local Shimano rep (assuming the hub's in warranty) or otherwise just spring for a new body. If it was a complete Shimano wheel you could just give the whole thing back to them - perhaps the one disadvantage of Open Pros!
 

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I have what sounds like to be the same problem. Mine is much more frequent. It's a loud clank, that people I'm riding with can easily hear from 7-8 bike lengths away. I've looked at everything, and I'm now convinced that it's the cassette. More specifically, it's the pawl or pawls failing to engage properly. It usually happens after coasting, or when starting from a stop. Mine is a Campy Chorus hub, but it sounds like a similar problem.
 

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Discussion Starter · #19 · (Edited)
Acttually, I've yet to try a different wheel, because the last thing I would expect is a faulty Ultegra hub. And the problem started almost immediately after I built the bike last year.

I've pretty much resigned myself to living with it, because it's rare and sporadic and doesn't really interfere with my ride.But sometimes, since this is my custom perfect designed-and-built-by-me lifetime retirement bike, this little glitch just bugs the p*ss out of me, like it did yesterday when I posted.

Thanks for all the thoughtful responses.Sometimes this board can be a damn fine place.

Ed

PeanutButterBreath said:
I am thinking the freehub is the source as well, but I would assume that a different wheel was tried at some point in the diagnostic process(?)
 
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