Originally Posted by
teledad
12 speed SLX derailleur, XT shifter, SLX 12-speed chain, all with about 300 miles. Was JRA and the shifting went from perfect to crap, skipping gears, double shifting. However I set the cable tension it isn't happy - if I adjust it just enough to shift up I can't shift down, adjusted just enough to shift down I can't shift up. If I leave it in the middle it skips cogs in both directions (particularly in the middle of the cassette).
First thought was the clutch, but turning off the clutch didn't help, and neither did a clutch service. Checked the derailleur hanger alignment, it's fine. Adjusted the set stop screws and the B screw, no change. Tried another wheel with a brand new cassette, same issue. Replaced the chain, same issue.
The derailleur seems basically fine, no slop in the pivots and it moves back and forth OK when I unhook it from the cable. Shifter seems to be working fine.
What's next - replace the cable and housing? New derailleur? New shifter?