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My derailleur keeps getting pulled up by the chain and jamming. The incriminating chain turned out to be quite streached and I have just replaced it but the problem persists! Maybee I should also chainge the cassette as it looks slightly warn although I don't see how that would affect the derailleur? Any advice would be much appreciated as I'm racing on sunday and am currently having a crisis!
Sounds like either your mech hanger or mech itself are bent. Stand the bike up and look from behind. The mech cage should be nice and vertical with the cassette.
Or, thinking about it, it could be a stiff link. Check your chain for a link that doesn't move easily. When you find it, use a chain tool to ease the pin in slightly to get it moving.
Ok tried that and I did have a stiff link that I have now fixed. Infuriatingly though it is till dragging up the derailleur!!!
Sure its the mech, not the front rings hooking the chain up?
Yep definitely the mech, I can see it happening.
have you checked the jockey wheels? as if they jam it can cause the mech to rise up like that.
If the old chain was [i]quite streached (sic)[/i]then the cassette is probably borked as well.
The jockey wheels are fine, bearings are ok, teeth only slight wear.
Your probably right about the borked cassette - but changing it won't stop the crazy rear mech? Plus it hurts me (financialy and phycologicaly) to buy a new cassette when the old one looks in good condition!
knackered cassette won't make the mech rise up like that, the only time I've seen it do it on my bike was when the jockey wheels were sticking, or when I was starting to get chain stuck and the chain started to rise up the chainring and the mech tugged it back down again, causing it to do a odd ticking movement and it freed the chain each time it started to stick.
Another thing to check is your freehub
If the cassette is knackered, the chain will skip forward over it and not sit on the cogs so you won't get any drive off it.
Freehub could do it. Is the freehub spinning freely? If it's got some resistance in it that'll cause the mech to rise up.
Thanks
The free hub is [i]very slightly[/i] stiffer than normal. I dont have much experience with free hubs, what do I do about this?
Does it do this in all three front chain rings, if it doesn't it is likely chain ring wear causing chain suck.
Ah Ha thats it, Bruce your a genius! It only does it in the middle front ring...so do i need to replace the cassette [i]as well[/i] as the front ring?
if you have killed the chain and the middle ring, you will be very lucky not to have killed the cassette.
Thanks everyone for your help. I'll change them both as I've found a cheap xt cassette. And of course I'll check my chain for streching in future.