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Problem shifting down - how do I fix it?

ForumNewbieForumNewbie Posts: 1,664
edited January 2008 in Workshop
I gave my chain I good clean with a rag last week and re-oiled it. Although I didn't remove the chain or adjust anything intentionally, I am now having problems trying to shift down to the smallest of the 3 rings at the front (the granny ring as I think it's referred). As I tried to change it down while going just slightly uphill it wasn't having it at all, and I found that I could only get it shifted down once I was back on the flat or slightly downhiil, but even then it was a struggle.

When I'm on the bike and in the middle chain ring and I look down at it, I see that the chain is not centred in the Front Mech cage so presumable that it the reason I'm having difficulty shifting it down. It's okay shifting back up to the middle ring, and going between the middle and large ring -it's just shifting down to the samllest ring that is the problem.

I am not bike-technical at all but I have consulted a maintenance book I was given. I think the Front Mech just needs adjusting but I am a bit nervous that I'll make things worse as I don't think the book describes how to fix it very well. It talks about the Low Gear and High Gear Adjuster screws which are usually marked H and L - but they don't appear to be marked on my bike. Can I try to adjust these on their own or would I also have to undo the cable-fixing clamp first as the book seems to indicate. I don't want to have to take the bike into the LBS if all that's required is some trial and error adjustments with these screws.

Can anyone please advise me what I should do?

Posts

  • CajunCajun Posts: 1,048
    Cable tension would be my first suspicion....
    Use the adjusting barrel to tighten it up....or at the front derailleur..

    http://www.acsu.buffalo.edu/~bmb/Bikes/ ... djust.html
    http://www.parktool.com/repair/readhowto.asp?id=75
    Cajun
  • John C.John C. Posts: 2,113
    In winter my first thought would be that it was starting to seize up, it is not uncommon for a front mech to work perfectly in the upper two gears but not at all for the Granny gear. So with the chain on the middle (bike stopped) click into granny and then see if you can push it any further with your thumb, if you can just apply lots of oil.
    http://www.ripon-loiterers.org.uk/

    Fail to prepare, prepare to fail
    Hills are just a matter of pace
  • Monty DogMonty Dog Posts: 20,614
    Clean under the BB cable guide - it can often get gunked up. Give the mech a blast with some WD40 or GT85 and give it a going over with a toothbrush to remove any accumulated gunk. Work the mech back and forth to get it moving. If that doesn't work, make sure the end of the cable is properly seated in the shifter and a strand hasn't splayed out and prevent the ratchet from seating home. I doubt it's anything to do with cable tension - 9/10 it's at the front mech itself because it catches all the censored from the front wheel.
    Make mine an Italian, with Campagnolo on the side..
  • ForumNewbieForumNewbie Posts: 1,664
    Thanks guys. One thing I do plan to get is a workstand which will make it a lot easier to clean the bike and get to these difficult places which may be a problem. A stand will also help me test changing gears etc. when I try to make adjustments.
  • Get that book and throw it out. You don't need to remove the cable cinch bolt to adjust the high and low limit stops...! :?

    I think the cable tension is slightly too tight. That means you have to slacken it. That means turning the barrel adjuster clockwise as you look down on it from where the housing enters the gear system. Slacken it 1/4 - 1/2 turn, and repeat. Anticlockwise tightens the cable. If in doubt, feel the cable tension and you'll quickly find out what way is right.

    It either that or the L limit screw is turned in too far. Slacken it 1/4 - 1/2 turn, and repeat. Look underneath the thing if you have to... that's a fast way of working out what's going on with the set limit screws! :idea:

    Or else you need to clean the derailleur mechanism & re-lube...
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