Just had my mech commit suicide into the wheel.

XTR mech, xt cassette not worn – sram chain not worn deore chainrings not worn.

JRA – down a steep rocky downhill changed gear from 5 – 7 clatter crash lockup wheel. One mashed mech.

I might have made a mess of the gear changing and still been in granny ring – but with the rear mech being in gear 7 it should have been well away from the spokes. No evidence of a stick, chain well lubed and not that muddy. Freewheel running nice and free, jockey wheels running free.

I would like to know what caused it as its the second time in a year and both times it was an xtr mech

Any ideas?

Limit screw not set?

mech hanger bent?

Set properly and I was changing up the gears so away from the spokes

sometimes if your decending fast with a loose chain the tyre can grab the chain.

You were in granny gear and 5 going downhill?

Popped spoke catching it and dragging it in?

What nonk said – I've seen that happen right in front of me!

Granny ring on a descent is the perfect scenario really – loose chain with the chainline almost as near to the tyre as it can get.

That's very interesting TJ. And hard to explain I agree. I read your post 3 times and can only think of one thing –

Must have been a rock strike which pushed it over, or general flappage on the rough surface. You can push a mech up the cassette if you try, so maybe loose chain effect from said flappage allowed the mech to jump up the cassette…?

EDIT
Granny ring grabbing chain sound plausable too

Druidh – the chain was on the granny ring when I came to a halt. I thought I was in middle 5 and changed to 7 – but it is possible I had missed the change from granny to middle. I don't think so – I think I was in middle – but its possible I was not. Quite a technical undulating bit of trail

wheel compresses as it flexes spokes bow out enough to catch bottom of your mech = end of the line for your rear mech 😮

wheel compresses as it flexes spokes bow out enough to catch bottom of your mech = end of the line for your rear mech

LOL!
This is TJ we're talking about, not Ton. 😉

Indeed PP – I was mincing down a series of rooty slippy rocky steps at o.o2 mph

thought you might have the gnarr factor turned up 😀

Did you fit it with a rock?

I was mincing down a series of rooty slippy rocky steps at o.o2 mph

AHHH! Now I'm the expert on this! I trashed one rear mech whilst PUSHING my bike when a stick got caught in it, and another at 2-4mph, same thing, but that took the mech hanger into the cassette with it….

I'm thinking stick interface now….

If the chain was on the granny and 7th the mch won't have been able to put much tension in it. It could be that both chain and rear mech were bouncing around so much that the chain was jumping off the jockey wheels and caught on the guide tabs on the mech cage.

Maybe?

granny and 7th (eg almost smallest) cassette sprocket will have had the chain flapping around on any kind of bumpy trail. Easy to then get caught in the tyre/wheel. As I said, I've actually seen it happen to the rider in front on a descent after a climb during SSMM a few years back when just the same he didn't shift out of the granny ring.

sometimes if your decending fast with a loose chain the tyre can grab the chain.

How does this send it into the spokes?

This sort of topic is rife for speculation – LOL at "wheel flexing" for instance. Not that I know what does it, seems a stick si most likely, and it's v hard to hit your mech off a rock in normal conditions.

No evidence of a stick

Could be chain tyre interface – but would that trash the mech? I can't see how it would

Could have jumped off the jockey wheels, jammed in the mech and then when I turned the pedals the mech would have got pulled round I suppose

I only run two chainrings so the chain has been shortened and has reasonable tension in granny.

the chain has a bust link as well – but I guess that happened after the event not before

How does this send it into the spokes?

It's a fair point.

I thought everyone knew it was because Mr Shimano gets lemmings to make the mechs. Some of the lemming dust rubs off and occasionally mechs just decide to end it all just like their makers…

Grumble mutter ruddy shimano mumble grump.

I hate chains and mechs. Only issue – I hate SS even more.

*sulks*

I've had it with a de-tensioned chain swinging my X0 mech in to the spokes on a gnarly descent. Hanger bent but didn't break, SRAM breakaway bolt did break and silly me I didn't have my circlip pliers with me to change it. Shortening chain to single speed was an oily and irritating affair.

Always descend on big ring front, 3rd/4th gear on back when I remember/have time to do it

Could have jumped off the jockey wheels, jammed in the mech and then when I turned the pedals the mech would have got pulled round I suppose

Sounds reasonable

the chain has a bust link as well – but I guess that happened after the event

Why? I'd suspect this has contributed.

Basically you'll never know, you just need to by cheaper mechs and learn proper mechanics 😛

I want to know!!!!! I want answers goddamit!!!!!!!! Fortunately the mech was bargainacious second hand. I learn you proper mechanics my boy. I been fixing bikes since you were in nappies

Never had it happen without limit screw mis-adjusted myself. Can't see how it would happen without serious flexing of the cage and I can't see that happening at low speed without an impact.

Done this many times.

Tyre catching chain

Serious chain suck.

Flexy back end

Flexy wheel

Chain flicking outside of the bottom jockey wheel under a hard shock, it then locks up as the load is reapplied and makes the mech turn itself inside out. Took me ages to work this out, but if you have chomp marks on the bottom of the mech cage its's probably that.

Or simply SRAM mechs that have grown tired of living.

was it bedded in properly?

Suicide?

Well it jumped into the wheel and now its dead.

Thats bikes for you. Time to batter the wallet again. At least its a cheaper hobby than powerboat racing.

It probably got terminally depressed at the sun being denied it by a traffic cone mudguard.

never had that happen. i always use xtr mechs.

🙂

tj, i think it's the confusion in your sub concious going from a tandem to a real bike 🙂 🙂