Join Date: Aug 2005
Location: Baie-Comeau, Québec
Bikes: Specialized Roubaix Comp '06
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Chain jump noise, only when down shifting and on 2 cogs
I have a tiny annoying noise problem that I'd like to fix if at all possible.. Here goes.
I ride a Specialized Roubaix Comp '06, I stuffed an ultegra 11-23 cassette and derailleur (10 spd), it came with 105 STIs. The problem happen when i downshift onto the 2 middle cogs of the cassette; It does a little jump once every revolution of the cassette. Looking at it in slow motion, I can see one of the smaller cog's teeth grabbing the side of the chain and lifting it, then the chain comes back down, making the noise that annoys me most. This only happen on two cogs as said before, and only when downshifting -- When I upshift onto them, the noise's gone. Also, a tiny nudge of the STI gets rid of the problem.
Here's what I (And my LBS wrench) tried so far: straightened the drop out, changed the cable and sleeves, and we tried a new cassette and chain on there. None of those things helped (same noise issue, same cogs). We've also tried the rear wheel on another bike and it still did it on there. After an hour of messing about, the wrench said it was a trademark of Shimano in general. I am not giving up, however.
What could possibly cause this? Please help.