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I have an old (2013) scott aspect 620 hardtail that I now use for bikepacking. Recently had the gear hanger snap, when replacing it noticed the rear derailleur is looking pretty bashed, cogs worn. Replaced the cogs/hanger, but next ride out the hanger snapped again on a benign trail with no strike or anything stuck. What I think happened is the chain came off the bottom cog and managed to lodge in between the lower cog and the cage (which shouldn't be possible?).
With that in mind, time for a new derailleur. A look on shimano's site shows the only 10-speed parts are for single/double front setups. Will they work with a triple (I've no interest in replacing the front).
The other thing that occurred to me is the last 2 hangers were from some online 'hangers for everything' replacement site, I wondered whether these are a bit weaker than the original one. The second breakage in particular seems to have had no force applied.
What matters is the dérailleurs capacity. Which is the range on the back plus the range on the front. So 42-22=20 at the front and 34-11=3 at the back. Thats a capacity of 20+23=43
The rear dérailleur doesn't care whether you are double or triple at the front
But you will need to match speed with your current set up
You might be able to pick up an old model online, but if not Shimano's Trekking kit is 3x10 and current (although rather out of date). They tend to be hard to pick up in the UK but not in Europe.
The rear mechs. have a 47 tooth total capacity and can handle a 22 tooth front ring difference. They're designed to run the trekking 48, 36, 26 chainsets with an 11-36 cassette but work quite happily with a 44, 32, 22.
[url= https://bike.shimano.com/en-EU/product/component/deorext-t8000/RD-T8000-SGS.html ]XT[/url]
[url= https://bike.shimano.com/en-EU/product/component/deore-t6000/RD-T6000-SGS.html ]Deore[/url]
Deore, slx, xt 10 speed all work on a triple if you make sure you get the long cage. (I still run a triple on my hardtail). I've had your problem before though and it's easily fixed with new jockey wheels and bending the cage back so the chain can't fall in anymore.
You need to learn how to adjust the high and low limit screws to ensure the chain can fall beyond the smallest cog (as I think you have experienced) or beyind the biggest (into the spokes).
Chain length needs to be just long enough to allow big front cog/big back cog to be chosen (although you wouldn't ever want to use that combo).
Too late to make a crucial edit to the above. Can - Can't error.
Adjust so the chain can't fall off the cogs is the important point.
Thanks all for the pointers. I should point out that this is nothing to do with limit screws - this is the chain getting wedged between the derailleur small lower (tension) cog and the cage housing it, not the cassette.
Are you on 9 speed or 10?
10-speed