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Front Mech not working

badbackbadback Posts: 31
edited December 2009 in Workshop
Hi all, my front mech won't change down from the large chain ring to the small one. It moves fine just doesn't seem
to move enough in order to push it down. Any suggestions, cheers

Posts

  • markos1963markos1963 Posts: 3,724
    Usually I find this problem is down to crud getting into the mech and the cable run. As the cable runs under the bottom bracket it picks up all sorts of stuff and bungs up the whole area. Just take out the inner cable and any outer ones in that area and give them a good clean and re-lube with a very light oil, the same with the front mech as well(without stripping it down) spray with a good degreaser and brush with an old toothbrush to get rid of the grime and then re-lube. 99% of the time it works for me.
  • jrabjrab Posts: 99
    Look here - pretty much everything you need to know - http://www.parktool.com/repair/readhowto.asp?id=75

    Pulling the cable moves mech to outer / big ring, so if mech won't change onto small ring suggests there is too much cable tension or cable is sticking.

    Other possibility is that the low limit screw on the mech is not allowing it to move far enough inwards, regardless of tension.

    1) Clean cables

    2) Check inner position of mech cage, if not far enough turn low limit screw (inner one on top of mech) anticlockwise a quarter-turn at a time.

    3) Ease cable tension by turning adjuster on down-tube or shifters (depending on your setup) clockwise a quarter-turn at a time.

    Tip - small adjustments, and remember how far you turned things......

    Richard.
  • markos1963markos1963 Posts: 3,724
    jrab wrote:
    Look here - pretty much everything you need to know - http://www.parktool.com/repair/readhowto.asp?id=75

    Pulling the cable moves mech to outer / big ring, so if mech won't change onto small ring suggests there is too much cable tension or cable is sticking.

    Other possibility is that the low limit screw on the mech is not allowing it to move far enough inwards, regardless of tension.

    1) Clean cables

    2) Check inner position of mech cage, if not far enough turn low limit screw (inner one on top of mech) anticlockwise a quarter-turn at a time.

    3) Ease cable tension by turning adjuster on down-tube or shifters (depending on your setup) clockwise a quarter-turn at a time.

    Tip - small adjustments, and remember how far you turned things......

    Richard.

    Totally right allthough I would suggest that the cable gets slacker rather than thighter so I wouldn't expect this problem to be caused by that and I would only check the limit screw after cleaning the cable and its disconnected.
  • jrabjrab Posts: 99
    The cage is always pulled by the cable towards the bigger chainring (same for the rear mech, pulled towards the bigger sprockets - unless you have a "top-normal" MTB mech) - the spring in the mech pulls it back towards the smaller chainring / sprockets.

    Think what happens when you work the shifter - push against tension to go bigger, click-release to go smaller.

    Hope that makes sense...

    Richard.
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