Bicycle Mechanics - Sluggish cassette up shift
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I have new Trance X-2 that has done this since the first ride. XT rear D and shifter with Sram 990 cassette. It downshifts to the larger cogs predictably, but the upshift is exactly the opposite. Sometimes it can take 3 or 4 complete pedal rotations to change or not change at all until I hit a bump. I tried over shifting then backing down to the gear and that doesn't work either. I snapped the original Shimano chain and the KMC now installed does the same thing. I suspect that the shifter cable is binding and not going slack immediately. The rear cable housing to the derailleur has quit a bend to it. Any ideas?
11-14-10, 08:42 AM
It sounds like you have diagnosed the problem - cable friction. Why not replace the RD cable and housing, eliminating the tight bends?
11-14-10, 08:46 AM
It sounds like either excessive cable friction (try lubricating the cable, or replace cable and casing) or the return spring on the derailluer is too weak (unlikely on a newer derailluer).
11-14-10, 08:52 AM
incorrect tension, try turning the barrel adjuster clockwise a click or 2. if its an xt shadow style then the b screw adjustment makes a big difference.
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.
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