So this should be fairly simple but I'm having problems, and hope the greater wisdom (ha!) of STW forum can help.
My ride had a standard 3x9 drivechain. Rarely used the big ring and then one day when playing around at a car park I ended up using it as a bash ring... that didn't go well. I decided to go 2x9 and replaced the big ring with a Hope bash, and changed the middle 32t (I think, maybe 34t) to a 36t to stretch the ratios out a bit. The jump down to the granny ring is larger, but not crazy. Didn't bother changing the mech or shifter they they still think there's a third ring that I just never use. Finally took a few links out of the chain to correct the length.
This seemed to work fine for a while but my last ride at Cannock there were problems: the chain was dropping off the middle ring quite frequently and then sometimes wouldn't switch from granny to middle, the mech would move and the chain would just grind mid-derail.
I didn't fiddle with the front mech apart from pulling in the H screw so I can't accidentally shift onto the bash ring. I'm wondering if I should drop the front mech now that it doesn't have to reach up to a triple, even though the middle ring is now larger... any other advice?
FWIW this is a SLX front mech from 2010 or thereabouts, M770 iirc. From my reading of the data sheet it can handle 22/36 fine.
Have you checked vertical clearance between largest ring and mech and/or cable stretch?
Sounds similar to a few issues I've had from time to time with a similar drive train setup wearing in and developing problems. Couldn't identify anything in particular so I end up doing a 'sort the basics' routine and it seems to sort it out.
sounds like normal deterioration to me. just apply a bit of maintenance. 😉
Good to hear that I've not done anything stupid so far.. 😉
If I remember correctly, when i did a 3x9 to 2x9 conversion I ended up moving the front mech up slightly - the shaping on the mech cage works best when the bit for the middle ring is lined up, and as I'd made the middle ring taller, the mech had to go up by a couple of mm.
But that was with a sub-Deore front mech. The cage shaping could be different on SLX.