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Can't change from big to small ring

Tovey9Tovey9 Posts: 6
edited December 2016 in Workshop
I have had problems changing from big to small ring. Firstly after adjusting cable it worked for a week then would not change again. My local lbs suggested a new front mech which they put on. It worked fine again for several weeks but now is stuck in big ring once more. The cable goes slack from taut when using lever but chain remains in big ring. I've had a new cable new front mech could it be the sti lever ? But I assumed if the cable goes slack it could not be that, any ideas.

Posts

  • If the chain is not moving then the FD is not moving far enough across to scrape it off the big ring so that it falls (with style) onto the small ring. If the cable is slack after releasing via the STI then the lever is doing its job by letting the cable out. So:
    1. Check the limit screws - it maybe that they are adjusted so that the FD can't move across.
    2. Cable tension - cables should be attached and tensioned when the FD is on the small ring, you then tension it further by moving it across by pulling on the cable.
    3. Is the FD positioned on the seat tube at the correct height? Technical guides will tell you where the outer plate has to be whether on the small or big ring (I can never remember).
    4. Is the cable moving smoothly inside the cable outer - it may be kinked or the inside corroded or clocked by debris. WD40 flushes stuff out or replace the cables.
    5. Is the FD free to move or blocked in some way? Cleaning it and checking the spring is an idea.

    Hope this helps.

    T
  • StillGoingStillGoing Posts: 5,207
    There are several possibilities.

    1. The derailleur setting is out.
    2. The derailleur is sticking.
    3. The derailleur is broken.
    4. The inner cable is sticking.
    5. The shifter is broken.

    Given that you've taken it to a dealer for them to fit a new derailleur and cabling, you can presumably rule out 2,3 and 4. If the cable is going slack when you change, the shifter is working ruling out 5. I would be amazed if a dealer hasn't correctly set the front derailleur, but it would appear to be the immediate suspect. Are you sure they actually put a new derailleur and cable on though rather than just gave it a cursory clean to appear so?
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • svettysvetty Posts: 1,904
    Did you replace all the cable or just the inner? is it sliding freely where it passes under the BB?
    FFS! Harden up and grow a pair :D
  • hsiaolchsiaolc Posts: 492
    Tovey9 wrote:
    I have had problems changing from big to small ring. Firstly after adjusting cable it worked for a week then would not change again. My local lbs suggested a new front mech which they put on. It worked fine again for several weeks but now is stuck in big ring once more. The cable goes slack from taut when using lever but chain remains in big ring. I've had a new cable new front mech could it be the sti lever ? But I assumed if the cable goes slack it could not be that, any ideas.

    You should take it back to our LBS and get them to look at it for you. This time find out the reason why it is doing this. Since it is happening to it before with hold front mech then it is not your front mech thats the problem.

    I think it is your front mech set up thats the main problem.
  • lesfirthlesfirth Posts: 1,204
    I think Svetty could be asking the right question. I had a similar problem. The cause was the cable had worn a groove in the plastic guide under the bottom bracket and the cable was sticking in the groove. I fixed it by filing the groove wider so the cable ran smoothly in the guide. Check the cable goes slack both sides of the bottom bracket.
  • hsiaolchsiaolc Posts: 492
    lesfirth wrote:
    I think Svetty could be asking the right question. I had a similar problem. The cause was the cable had worn a groove in the plastic guide under the bottom bracket and the cable was sticking in the groove. I fixed it by filing the groove wider so the cable ran smoothly in the guide. Check the cable goes slack both sides of the bottom bracket.

    If thats the case then he should be sticking even after he changed to new FD and cable. He had a few weeks of working system.

    It is possible something is sticking.
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