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I have a mixed 12-speed drive train on my gravel bike it’s an XT shifter, Deore mech with a GX chain and a 10-50 cassette. A few months ago after about 5 rides I was getting it ready to ride on hols I pushed the bike out of the accommodation into the town square I got on the bike to pedal and the whole thing was locked. When I examined the bike the inner plate of the rear mech was destroyed, it had folded at the outer jockey. It was working previously and it hadn’t been touched since. Luckily the bike shop in the town replaced the mech that day, at the time I had a 9-50 ZITTO cassette on it, I was convinced it was the cassette's fault so when I replaced it with a 10-50 GX when I got back.
A few weeks ago I was getting the bike ready for my next holiday, I was swapping the bars for some loop bars, as I did this I also clicked the right shifter a few times as I’d staved my thumb in an OTB and was having trouble shifting so I was trying to get the most comfortable position. Once everything was done I pushed it out for a test ride and the same thing happened. When I started peddling the chain didn’t move down the block as you’d expect it stuck and again bent the plate of the mech.
I haven’t investigated further as I had to prioritise getting my old gravel bike ready for the holiday as it was set up as a winter road bike. I’ve ordered a new mech and some SLX plates to try to recover the damaged mechs. My next thought is to check the chain for damage/stiff links and I’ll probably replace the chain anyhow for good measure. Is there anything else to try, is there any incompatibility between a GX 12-speed chain and a 12 speed Deore mech?
I'd say that the mech is hitting the cogs on teh cassette and getting messed up like that, maybe the B-Tension is wrong,
Thanks I add I’ll check for that tonight too. I’m both case it occurred after the bike had been pushed and then resumed riding rather then during a ride.
Are you sure the cable isn’t to blame? Is it routed correctly?
I’d go with b tension and also check the chain length, as it can mess with correct b tension
My first guess would be the chain being too short.
Was the OTB on the gravel bike?
@matt_outandabout No it was coming into Seathwaite half way round the Walna Scar route. I don't know the path but at the its a bit of a boulder field. I was on a hardtail.
I had to ride/push the rest of the route with two sprained wrists and a staved thumb. I could brake but I couldn't change gear. It wasn't much of a problem as I pushed all the way up and half the way down. I was a seriously underbite/underfit.
I did go OTB last year on a freak accident on a gravel bike on a quiet road and ended up in Salford Trauma unit.
Ok - I was looking to blame a crash for a broken derailleur...
I'd say b tension too
The cages are soft and I assume designed to be sacrificial, they bend these days when they go in the spokes rather than destroying the wheel
The cages are cheap and easy to replace, you can never bend them back quite right
, I was swapping the bars for some loop bars, as I did this I also clicked the right shifter a few times as I’d staved my thumb in an OTB and was having trouble shifting so I was trying to get the most comfortable position. Once everything was done I pushed it out for a test ride and the same thing happened. When I started peddling the chain didn’t move down the block as you’d expect it stuck and again bent the plate of the mech.
Not sure if I'm reading it right, but did you make multiple down clicks while the bike was static, then wheel it outside, jump on and start pedalling?
If so, I know that often things can get hung up like that because of the extreme angle the chain tries to take and you could potentially do damage. Always best to spin cranks as you try shifters or at least cancel down shifts out with up shifts.
Might have misunderstood what you wrote.
That's exactly what I did the second time it happened , I understand that I should have span the cranks around before riding it. Ive never had that problem before normally the chain would shift into place maybe its the more extreme chainlines you get with 12 speed 1x. But its happened twice now with a new bike.
Yes, I would personally never make multiple shifts without also turning the cranks.
If you get on the bike, then pedal, the chain is trying to leap across lots of cogs, under load, and sometimes (ime) will get hung up.
I can imagine if you're putting the drivetrain under load this potentially causing a lot of damage to the mech.