The other week, riding in the peaks, I got to the bottom of a famous rocky descent, the name of which escapes me, started to pedal out up the fireroad and my mech tried to bury itself into my spokes jumping off the top of the cassette. I stopped instantly so no damage.

Bent mech!…you say? Well no, it seems fine actually, and I’ve bent enough of them to recognise a bent one.
I tried to sort it trailside, but no amount of inward adjustment of the B-screw would make the mech clear the biggest ring on the cassette, and consequently it would not change down the cassette as it was stuck ‘riding’ the biggest ring.

I’ve taken the mech off tonight, cleaned and inspected it, got the jockeys spinning well, looked it over and all seems fine. My mech hanger(part of the frame in this case, it’s a Dialled PA) also looks just fine.
However, it still rides the biggest ring and no amount of B-screw adjustment will stop it riding the ring, it also seems close to the spokes when on the biggest ring with not much tolerance between hitting the spokes and changing down a cog.

Also, weirdly, now with the bike upsidedown and in the smallest cog(It’s a 1×9) the chain seems too long and the mech is very horizontal.

Anyone have any ideas or recognise some of these issues? I can’t see what the problem is to be honest…

Something similar happened to me and it turned out to be the rear hub had collapsed internally. Worth having a look.

pics?

Sticky cables? Badly routed cables?

Is it shimano? The B tension screws never seem to do much on their mechs.

matt_outandabout – Member
pics?

The whole shebang, chain on largest ring

Chain on smallest ring

Rear view

Chain on biggest ring, riding the ring and stuck there despite full, inward adjustment of B-screw.

B-screw wound fully in, still not preventing the mech riding the cassette on the bigger rings

Sticky cables? Badly routed cables?

Is it shimano? The B tension screws never seem to do much on their mechs.

Its Sram. It’s worth mentioning that I have been riding this bike week in, week out with this setup and no problems for ages.
Cable is fine, free-pulling..

I THINK it may be sorted. My wheel was very hard to remove, diagnosis? Bent mech hanger/frame 🙁

It didn’t look bent but putting a straight edge across the dropout it looked to a be a mm or so deflection and bent slightly forward too, hence, difficult to remove the wheel…

I think the mech is damaged in some way though as I’d be surprised if the hanger could get bent without damaging the mech a bit.

Anyway, it seems to shift relatively ok now and the top jockey wheel isn’t riding the cassette…
🙂