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Old 05-23-12, 12:37 AM   #1
damonwang
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click-click-click vibration in pedals in all gears after installing new cogs---help?

I have a 1982 Schwinn Voyageur with a 14-28 7-speed freewheel that's been developing a lot of play. It's so wobbly it makes an audible clicking noise as I pedal. So today I installed a new Shimano 7-speed 13-28 freewheel. Now the old clicking noise is gone and it sounds lovely and silent and smooth on the stand, but on the road I can feel a click-click-click sort of vibration in the pedals in all the gear ratios (any chainring, any cog). The closest I can describe it is, it feels the way a single-speed sounds if you over-tension the chain. I feel it only when pedalling, not when coasting, and I haven't changed anything in the crankset, bottom bracket, or pedals. There is no skipping and it shifts just fine.

Here are a few things that we've tried between the LBS mechanics and me:
- measured the chain: using one of those Park Tools gauges that you try to drop into the links, the chain is under .75% wear.
- adjusted tension and limit screws on the rear derailleur
- replaced an inward-facing screw with a shorter one that stops well before hitting any teeth on the smallest cog
- wiped and re-lubricated the chain, jockey wheels, and derailleur pivot points
- removed and re-installed the rear wheel like five times to make sure I wasn't putting it in crooked
- wiggled the freewheel to make sure it was screwed down tight and there was no play in the bearings
- wiggled the rear wheel to make sure there was no play in the hub

The guys at the LBS are scratching their heads too, because usually one of the above will fix it. (Actually, in their experience, one of the first three or four should fix it.) The last hypotheses they haven't tested yet:

- the chain is under insufficient tension because the derailleur is not pulling back strongly enough or the chain is too long, which sounds unlikely because the clicking is equally strong in all gears and also the new cogs are only one tooth off from the old ones.
- This is some kind of weird period of mechanical run-in that will resolve itself after a few hundred miles, which is unlikely because these mechanics have installed these cogs on many other bikes without such problems

Anyone know of any other ideas we could try?
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Old 05-23-12, 05:28 AM   #2
dsbrantjr
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Don't trust chain gauges. Measure your chain with a good steel rule. 12 full links should measure exactly 12 inches when new; if the chain has worn to where the measurement is 12 1/16" (about 0.5% wear) or more replace the chain. Running a worn chain on new cogs will cause rapid wear on the cogs; the load is carried on only a few teeth and the vibration you feel may be the chain engaging and disengaging from those teeth.
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Old 05-23-12, 05:36 AM   #3
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Yep, it's the chain. New cogs, new chain. Chains are cheap. It does not need lots of wear to not match the brand new cogs. The bike shop should have already tested it by putting on a new chain. As already posted, you are wearing out the new cogs now as you ride.
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Old 05-23-12, 10:01 AM   #4
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I just measured the chain with two different steel tape measures, and twelve links deviates from twelve inches by less than the width of the twelve-inch line on the tape measure. But I'll take it back later today and try a new chain.

FYI, down at my end of the market, a freewheel costs about as much ($10) as a new chain. I'm not running a Campy Record groupset here.
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