setting up front derailleur

bonj2

Guest
in re setting up my gears on my road bike my front mech has now got a problem, whereby it sometimes throws the chain right over the big ring. It seems that it is shifting it such that to start with, the very edge of the chain is resting on the very edge of the chainring, and then if it falls 'inward' it goes on ok and if it falls outward then it's come off.
I'm sure it isn't the limiter screw, as i've got it so that the mech can only move just far enough for it not to rub when it's on the big ring. Thought it might be a bad chain line or the chain being too loose, but don't think it's either of these as albeit possibly slightly less, it still does it when the rear mech is on the larger sprockets. I've tried it at different tensions so many times that i've knackered a cable so need a new one tomorrow. :smile:
any ideas of avenues of investigation greatly appreciated.
 

Smokin Joe

Legendary Member
Have a look to see if the mech cage is parallel to the large chainring, running it even slightly out can cause problems.
 

Dave5N

Über Member
If the hanger's bent it throws the chain.

I am sure you knew that.
 
Dave5N said:
If the hanger's bent it throws the chain.

I am sure you knew that.
That I did but bonj was not saying the chain was coming off on the rear its the front chainring. Which means that he 1) Moved the mech and cant get it back to the same spot. 2) He's put a new cable in and got the tension wrong. 3) He had a look at the limits and had a play. 4) The shifter is not working right. None of witch have to do with the rear drop out.

bonj said:
in re setting up my gears on my road bike my front mech has now got a problem, whereby it sometimes throws the chain right over the big ring. It seems that it is shifting it such that to start with, the very edge of the chain is resting on the very edge of the chainring, and then if it falls 'inward' it goes on ok and if it falls outward then it's come off.
I'm sure it isn't the limiter screw, as i've got it so that the mech can only move just far enough for it not to rub when it's on the big ring. Thought it might be a bad chain line or the chain being too loose, but don't think it's either of these as albeit possibly slightly less, it still does it when the rear mech is on the larger sprockets. I've tried it at different tensions so many times that i've knackered a cable so need a new one tomorrow. :?:
any ideas of avenues of investigation greatly appreciated.
 
OP
B

bonj2

Guest
it could well be possible that the fact it is throwing over the front big ring could be due to a bad chain line, and a bad chain line could be due to the REAR mech hanger being bent. I don't think it is though, as the mech hanger has not had cause to become bent (i haven't knocked it or anything) and I didn't have this problem before.

I went to an LBS to get a new cable and asked about it on the offchance, and they said they could have a look at it by tomorrow if i left it with them, so i have done, I'll know tomorrow what it was that was the problem. I suspect going back to basics and re-setting up the front mech according to sheldon's guidelines (cheers spandex) and checking the rear derailleur hanger isn't bent will sort it, but i'm not averse to paying a measly few quid to let somebody who can do it a lot quicker than i can have a go simply because they do it many times a week.
 
OP
B

bonj2

Guest
well the bike shop i've took it to have identified a perfectly legitimate reason why it's doing it, and it needs a new part. unfortunately though they haven't got that part in stock so i'm going to pick it up and go to another bike shop to try and get the part and then probably fit it myself.
 
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