Strange front gear change problem

wilwil
wilwil Posts: 374
edited September 2008 in Workshop
This is a new phenomenon that has started. When changing from large ring to small ring the chain is taken off the large ring okay but then fails to engage with the small ring. It just seems to get stuck above the teeth and the cranks turn with out doing anything. Then I have to quickly unclip before falling over. This happened yesterday and today and the only thing I've done between the last ride and this one is clean and rel ube the chain.
Any ideas?

Centaur 10 speed compact.

Comments

  • cable stuck? stone in the front mech? spring broke?

    put it in the smallest ring and try to move the mech by hand. I had this with my mtb once, a small stone had lodged in the mech preventing it coming all the way inboard.
    --
    Burls Ti Tourer for Tarmac, Saracen aluminium full suss for trails
  • wilwil
    wilwil Posts: 374
    cable stuck? stone in the front mech? spring broke?

    put it in the smallest ring and try to move the mech by hand. I had this with my mtb once, a small stone had lodged in the mech preventing it coming all the way inboard.

    That's the strange thing, the mech is moving quite normally.
  • neeb
    neeb Posts: 4,470
    I've had this problem and never quite figured out what it was, partially because it seemed to go away on its own eventually. Perhaps if the limiter screw that stops the chain coming off the inside of the small chainring is just a little too far in, the chain can't quite get far enough in to engage with the teeth in some circumstances, e.g. if it is under load, even if it works fine on the workstand. You definately didn't tweak the limiter screws when you were cleaning & lubing the chain?

    When this did happen to me it was always on hills, and usually after changing up at the back and then down at the front immediately afterwards. Now on steepish hills if I am going to change to the small chainring I do that first, and make sure it is engaged before changing up at the back if necessary.
  • topdude
    topdude Posts: 1,557
    Long shot suggestion, you have a very worn chain so it is too flexible in a side to side direction. This lack of sideways stiffness allows the chain to fall between cogs rather than moving directly to the small ring.
    Compare the chain to a new one and i bet it is much more flexy side to side :?:
    He is not the messiah, he is a very naughty boy !!