Front derailleur chain rub middle ring

thebluevoice
thebluevoice Posts: 31
edited June 2015 in MTB workshop & tech
Hi,

Firstly, it's a Shimano XT setup, 2014 Ghost AMR 2975..

On one of my bikes the chain is rubbing on the inside plate of the front derailleur.

This only occurs when using the front middle ring (3x setup) and the largest 4 cassette cogs (10 speed).

The front shifter barrel adjuster didn't seem to cure it...

The derailleur is fixed directly to the frame.

Any ideas where to start most welcome - should I start twiddling the L & H screws maybe?

Thanks!

Comments

  • The Rookie
    The Rookie Posts: 27,812
    L and H screws will have no effect at all, they are stops to prevent teh chain coming off inside the inner or outside the outer ring and are not doing anything at all in the middle ring.

    cable tension, increase cable tension to pull the cage out slightly further, also check for a bent (or not correctly mounted) ring which would mean it rubbing almost whetever you do.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • Chunkers1980
    Chunkers1980 Posts: 8,035
    I'd start by reading the Park Tools website on Mech setup before twiddling anything randomly and hoping.
  • thebluevoice
    thebluevoice Posts: 31
    Thanks, I'll leave the screws alone :)

    Since I'd turned the barrel adjuster as far as it would go to loosen the cable and it still rubbed, I let about 3mm slack by loosening then tightening the cable grip screw on the f.d.

    This has helped, but not fully cured..

    I can either (by fine tuning with the barrel adjuster) have noiseless front middle ring or smooth shift up from front small to front middle. But not both?!

    The rings look true. The chain looks to be parallel to the f.d. The f.d is directly mounted, not via a band clamp, can it be adjusted?
  • The Rookie
    The Rookie Posts: 27,812
    Slacker cable will make it rub more, so not the best plan, perhaps you should, start from fresh now you've made a hash of it!
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • thebluevoice
    thebluevoice Posts: 31
    [url=http://www.bikeradar.com/forums/viewtopic.php?p=19631774#p19631774]The Rookie[/url] wrote:
    Slacker cable will make it rub more, so not the best plan, perhaps you should, start from fresh now you've made a hash of it!

    Hmm, now I'm confused. Slackening the cable moved the derailleur inwards and stopped the rubbing. The chain was rubbing on the inside plate you see..

    Why do you expect it to rub more when it didn't?

    Cheers :)
  • The Rookie
    The Rookie Posts: 27,812
    Sorry, I misread it as 4 smallest cogs.

    That said, now you've thrown out the indexing, you may as well start again.

    Check for the following
    1/ bent chainring
    2/ Correct mech height so that the steps align with the gaps between the chainrings
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • dgunthor
    dgunthor Posts: 644
    changing the angle of the front mech can help too
  • thebluevoice
    thebluevoice Posts: 31
    [url=http://www.bikeradar.com/forums/viewtopic.php?p=19631950#p19631950]dgunthor[/url] wrote:
    changing the angle of the front mech can help too

    Yes, I think a small adjustment (1mm or so) towards the back would stop the final bit of rubbing. how do I twist the f.d - its held on with two bolts at the bottom - not a clamp band?
  • The Rookie
    The Rookie Posts: 27,812
    You can't, its direct mount, but there should be some height adjustment available
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.

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