I recently replaced my drivetrain with an XT 10-51 12sp cassette, XTR chain and upped my chainring to a 32 from a 30, replacing the original SLX parts on my '23 stumpy carbon comp.
Everything works flawlessly, apart from shifting from 9th into 8th. I always have to overshift a bit, every single time else it'll just stay in 9th clacking away forever. All the other gears work fine, as does the opposite direction through the entire range, it's just that 1 gear in that 1 direction. The offending gear being the one that sits between the main cassette block and the thicker spacer.
The cassette spacers are correct, I've adjusted the b screw as per Shimano instructions, the cable is fine and runs smooth and I'm at a loss as to why I'm having this issue. Everything was fine with the old SLX kit too so don't think it's a mech alignment issue.
If I add cable tension so it shifts ok, then the chain catches on the bigger (lower) gears throughout the entire main block and everything is quite horrendous, and shifting into higher gears becomes unreliable. It feels like a spacer issue, but according to the exploded diagram, there are only 2, and they are in the correct places.
Any ideas? I have some time off work soon so going to investigate more thoroughly then.
by No-Sherbet8709
5 Comments
Are your shift cables new? I encountered a similar shifting issue with my bike, and replacing my tired shift cables, re-setting my limit screws and b screw, and a few minutes of indexing did the trick.
Maybe an damaged theeth ? Or this gear is more worn then the others.
The installation direction of that cog? Is it facing the right side?
Pull the cassette apart and re-assemble. The tolerances on the 12-sp stuff are pretty fussy.
Did you check the hanger alignment with a derailleur alignment guage? I’d also try reinstalling the cassette and making sure it’s torqued properly.