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Old 07-17-11, 06:24 PM   #1
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Inconsistent, slight hesitation and "clunk"

I have a Phil Wood BB,with FSA SLK cranks; both of these are pretty new to me, having been installed by the LBS in the past couple months (about 1000 miles in dry conditions, no reason the BB should need servicing) . The bike is a Bianchi Via Nirone (aluminum frame w/carbon rear triangle).

I have a potential issue, in that, occasionally, when I start pedaling I feel a very slight hesitation (like something isn't engaged properly), there's a slight "clunk." Then everything works like it should. This doesn't happen often, maybe once or twice a ride. It never happens after a shift (just to say that it isn't a shifting problem, I think), but always when I resume pedaling after I had either stopped or coasted; this is the only variable, and it doesn't happen when I hit bumps or anything. It only happens once at a time, like a knuckle that pops and then works fine, and it doesn't cause me any trouble. Just worried it's a sign of some problem.

I took it to the LBS and asked them to check the tightness of the cranks, and described what's happening. It checked out ok, but they said to try to pinpoint when it happens better, since the only thing I can really say is "it goes clunk sometimes. infrequently, and pretty much unpredictably."

My old FSA Gossamer cranks (w/stock BB) used to come loose. That's why I thought the cranks were loose.

Anyone have any good suggestions for diagnosing this?
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Old 07-18-11, 07:46 AM   #2
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It has nothing to do with the cranks. It's a lag in the freewheel engaging. The tip-off is that it happens when you resume pedaling after coasting, and it may or may not indicate a problem.

Depending on your hub, there's varying amounts of dwell in freewheel engagement. You can see this if you stand the bike up and back pedal a tiny amount until you hear the click or the freehub pawls drop into the next ramp, and re-engage. Estimate that amount of free movement, back pedal as far as you can before the click, then push forward suddenly, and you'll duplicate the clunk.

As I said, it may or may not be a problem. Normally it's just a few degrees but can feel like more because the wheel is running away from you. But if the pawls are damaged, or sticky, the spring may be slow to return them causing a delayed re-engagement. You have to decide which based on a judgment call. If you suspect the hub, or it was recently serviced (many shops over-grease the ratchet) have the hub field-stripped and serviced.
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Old 07-20-11, 12:53 AM   #3
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What's the rear hub? If it's Shimano, you can replace the cassette body quite cheaply and easily. Or overhaul it.

With other hubs, YMMV. Should be possible to overhaul pretty much anything though; I'd clean and re-lube, and maybe add some tension to the pawl spring/s.
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