Front derailleur issues

badhorsy
badhorsy Posts: 107
edited December 2010 in Workshop
Hi all,

I've got a triple chainring. I've somehow lost the ability to shift from the middle to the bottom chainring - the deraileur moves without a problem, but the chain does not seem to move with it. Shifting up is fine, and also shifting down from the top to middle. No problems with the rear either.

I've tried using the barrel adjustor to loosen the cable tension, but it doesn't seem to be making a difference.

Any ideas?

Comments

  • desweller
    desweller Posts: 5,175
    What is the make and model of your shifter and derailleur? Try unscrewing the bottom limit screw a little.
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  • Wheelspinner
    Wheelspinner Posts: 6,574
    Or cleaning out where the limit screw hits the derailleur body... maybe some cr@p stuck behind it blocking the movement. ALso clean your shift levers... sticky ratchet limiting movement in there?

    Last check is clean and grease cables thoroughly.
    Open One+ BMC TE29 Seven 622SL On One Scandal Cervelo RS
  • badhorsy
    badhorsy Posts: 107
    Sorry, should have mentioned - its a Shimano 105.

    Don't think it's a limit screw thing - actually got the gears service a few weeks back. This is kind of an overnight problem that seems to have developed...
  • keef66
    keef66 Posts: 13,123
    Is the cable slack when the mech is over the small chainring? If so it sounds like the cage isn't moving quite far enough. If you're sure it isn't the limit screw stopping it, release the cable clamp and move the mech back and forth repeatedly. Squirt a bit of WD40 on all the pivot points, wipe off and repeat with light oil.

    If the cable is still tight when the mech is over the small ring, check that the shifter has run out of down clicks, then release the cable clamp.

    In either scenario, reattach the cable at the clamp and set up from scratch as per Shimano instructions.
  • Buckled_Rims
    Buckled_Rims Posts: 1,648
    badhorsy wrote:
    Sorry, should have mentioned - its a Shimano 105.

    Don't think it's a limit screw thing - actually got the gears service a few weeks back. This is kind of an overnight problem that seems to have developed...

    If you don't think it's an adjustment or cable problem then Google "Shimano 105 left hand shifter problem" and gulp at how many have broken. There seems to be a fault in what Shimano has done to the 105 LH shifter in that it's both a double and a triple shifter in one.
    CAAD9
    Kona Jake the Snake
    Merlin Malt 4
  • desweller
    desweller Posts: 5,175
    If the mech is moving, but not shifting the chain, then it's because it's either not moving far enough or it is not correctly installed. They can go out of fettle quite easily - for instance if the mechanic has not tightened the retaining screws enough or something like that.

    There are quite a few things it could be, but most of them can be solved by going over the setup of the mech in a methodical fashion.

    Have a look at Park Tools for front mech setup.

    FWIW I'd say it's pretty unlikely to be the shifter.
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