Originally Posted by
rothenfield1
The replacement cassette I just put on is a used Ultegra.
I'm going to assume the freehub is alloy, but not sure.
The shop mechanic put the shim in, I don't know what size it was.
I haven't ridden these wheels in several months, but my initial complaint was skipping between about the 7-8 cogs. The mechanic first thought it might be a bent hanger, but that checked OK. He was getting frustrated by not being able to smooth out the shifting when he noticed the wobble, he put a shim in it and suggested that I might need a new cassette. I just put on this used Ultegra and when you spin the wheel will looking straight down over it, you can see the cassette weave in and out as much of an eighth of an inch. These wheels are supposedly new Mavic CXP-22 laced to generic Specialized branded hubs. It's almost as if the freehub is not centered on the axle.
1. Verify that the rear wheel is properly dished - using NOT the arms of the dishing tool for reference - but rather USE center-point-on-locknut for reference.
2. Then if wheel turns out to not be dished - get it dished THEN fix the hanger alignment.
If at that point fiddling with barrel and screw adjusters doesn't fix the problem - the issue is elsewhere. I.e., housings, brifters, bent derailleur, cassette and chain wear mismatch, ferrules, etc...
Even wobble of an 1/8 of an inch will have minimal impact on shifting performance.
=8-)