Why didn't my emergency repair work?

gbl

Hi all,

I was out writing with a buddy the other day and randomly both of our rear mech's went bottoms up at the same time. I tried to do a qucik change to single speed to get us both home with mixed results. We removed our mechs and shortened the chain accordingly and ran it on the smallest ring (of 2) and a nice, middling cog. His worked a trreat and he cruised home no problem, mine however wouldn't play cricket at all. The chain kept jumping into a biggert cog until the chain was so tight you couldn't peddle or remove it! I enede up taking the whole thing off and pushing home while he sailed off into the distance...

Any one know what the problem with my bodge job was and why it worked on hist Kona Stinky but not my Norco shore?

nicklouse

different mech operation

poor cable routing.

gbl

thanks for th (very) quick reply! Not sure i get it though. Why should my rear mech make a differenbce when it wasn't plugged in? And why would poor cable routing make any difference for the same reason and as it working bang on until then?
Cheers

Daz555

You'd have to compare chainlines to see if your setup was more crossed than his and perhaps causing your chain to shift.

Rockhopper

I think that modern cassettes will try and shift the chain up the cogs itself becasue of the way the teeth are shaped. The mech actually stops it changing gear on its own. Thats why its normally very difficult to do away with the mech all together if you do have a breakage.

Matt 24k

A modern cassette is always trying to move the chain up towards the wheel. They are machined this way and the mech holds the chain in the desired gear. Cable ties have been used to try and hold the chain in position and this sometimes works. Not sure why your mates bike wasn't shifting up the cassette. Maybe he doesn't pedal as hard as you

gbl

ok thanks for the info about the mech always trying to change up. I was just curious really as the books say it's an emergeny option when the derailleur breaks but from what's said on here it sounds like it shouldn't work with a modern cassette!? Am i right in thinking then that next time it happens i have to break the che chain so that the tension is right for it so sit on the largest sprocket so that it can't move any further up?

Thanks again for all the info, much appreciated. And yes, i do pedal harder than he does!

Daz555

Interesting to read about the chain climbing towards the wheel by default. Didn't realise that. If the dérailleur is counteracting that effect it must surely add a lot of potential for wear on the chain and sprocket.