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Chain falling off small ring

obizzleobizzle Posts: 28
edited May 2010 in Workshop
Hi all

I'm having a problem which I assume is associated with my gear cable to my front mech stretching - the chain can fall off the small ring, and only just makes it onto the big ring, but with terrible trim.

should I:

a) retension the cable

b) adjust the inner and outer limits on the front mech

c) retension the cable and adjust the inner limit of the front mech (because as I understand it, regardless of tension, the limit should stop the mech dropping the chain)

d) something else.

Thanks a lot :)

EDIT: title change


  • John.TJohn.T Posts: 3,698
    Try c) first. You are right. The limit stop is what stops the chain from dropping off the inner ring. A stretched cable will stop the shifter pulling enough cable to get on the big ring easily. Over shifting is controled by the top limit screw.
  • BobbinogsBobbinogs Posts: 4,841
    Chaps, I have the same problem as obizzle and dropped the chain twice today on hills (grrr). Can I ask a dumb question, what is the limit stop?

    I had a look on Sheldon but his picture of limit stops shows them located on the derailer.

    On my bike I have a plastic thing on the seat tube and it looks to be a bit too far away to stop the chain falling off. Is this the limit stop or is the limit stop part of the gear mech (and the plastic thing just a "belt and braces" gizmo)?

    Many thanks in advance (obizzle, hope you don't mind me piggy backing).
  • gbsgbs Posts: 450
    Happened to me twice but not since I fitted a Dog Fang.
    vintage newbie, spinning away
  • keef66keef66 Posts: 13,123
    Bobbinogs; the plastic thing is indeed the belt / braces / bicycle clips gizmo. It's a Deda dog fang as mentioned in the next post by gbs. It should be positioned so it's virtually touching the chain when in the smallest ring / biggest rear sprocket.

    The limit stops are the little screws located on front and rear derailleurs.
  • satanassatanas Posts: 1,303
    With some set ups a Dog Fang (or equivalent) is a necessity if one wants to be able to shift to the small ring without dropping the chain. Also handy for preventing scratches on those expen$ive carbon chainstays which might then later snap!
  • BobbinogsBobbinogs Posts: 4,841
    Thanks keef66. I checked the dog fang and it was indeed set too far away. I have moved it forward as you suggest (it was the nice and easy solution) and couldn't get the chain to drop when testing. :)
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