Chain rub on front derailleur when under load.

SPOC
SPOC Posts: 109
edited July 2013 in Workshop
When in a stand, it all runs fine. I am running a 34-50 with a 10 speed 11-25 cassette. I can get it in the stand, all shifting nicely on all the gears bar the 34-11 and the 50-25 (To be expected?).

However when you put force through the pedals,(i.e riding it) it seems to send everything left and I get noticeable chain rub in the 34-(25,23,21,19) and chain rub right through the 50 ring from the 25 through to the 17 cog. Least being annoying, it can't be good for the chain.

The bracket to attach the derailleur is mounted to the carbon frame and can't be twisted sideways or moved up or down.

I've even taking it to my LBS who doesn't really believe me I got the impression, a few nods and saying he knew what to do and it's back with the same problems, if not slightly worse.

I really don't want to start messing about with it too much and make the problem even worse, but I am pretty practical and tend to work out stuff as I go on, just haven't really encountered anything like this before and it's giving me a headache to solve.

Any ideas appreciated,

Cheers

Comments

  • thefd
    thefd Posts: 1,021
    Try adjusting the high and low limit screws on the front derailleur.

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  • sungod
    sungod Posts: 17,357
    could be wromg cable tension, could be limit screws, could be both, but the rubbing under load suggests something is flexing

    best to set up the fd from scratch - undo cable, back out limit screws, then go through alignment and adjustment from the beginning

    if you already did that, try to determine what is flexing and how this is causing the effect, putting the bike on a turbo while someone watches for instance
    my bike - faster than god's and twice as shiny

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