Join Date: Apr 2009
Location: New Rochelle, NY
Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter
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It could be a poor trim adjustment, biased toward the inside of the cassette as reptilezs says, or cable friction which presents exactly as you describe. I always suggest eliminating the easy stuff first, so back off the barrel adjustment until downshifts are sluggish, then re-tighten just enough to make them barely acceptable, and see if that helps. If so, then adjust for the best balance between both directions.
There's an easy diagnostic for cable friction. Ride and upshift one gear as usual, if it doesn't respond immediately, pluck the bare wire away from the downtube like a guitar string. If it solves the problem you have too much cable friction. Field strip the cables, replace any kinked section of housing, check that housing ends aren't crushed, lube with a very thin oil, or teflon lube, and re-assemble.
The other test for cable friction is to shift through the gears on a repair stand. Loop a piece of string around the lower body and shift in both directions keeping light tension on the string to help the RD return spring. If the added tension makes a difference in upshift response then it confirms a cable friction diagnosis.
An ounce of diagnosis is worth a pound of cure.
“Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin
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