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front gear adjustment

Discussion in 'Bicycle Mechanics and Repairs' started by Kestevan, 16 Apr 2008.

  1. Kestevan

    Kestevan Last of the Summer Winos

    Location:
    Holmfirth.
    I have a slight problem with the adjustment on the front mech (Tiagra double).

    When I'm running in the lowest gear, the chain is "slightly" rubbing on the fron cage. If I move the adjustment screw so that the chain rub stops, then I cant change down from the outer front ring reliably.

    All the other gears appear ok, and if you push the front cage back in to the frame slightly with your fingers the rubbing stops. It looks like its just not moving back far enough onto the stop if that makes sense.

    Any ideas on how to cure this?

    Cheers
     
  2. leoc

    leoc New Member

    Location:
    London
    Could be that the cable isn't totally free to move and therefore the cage isn't returning all the way to the low stop reliably? You could inspect the cable and lube or replace if necessary?
     
  3. Tynan

    Tynan Veteran

    Location:
    e4
    spanking new bike with double here and it started doing this almost immediately, after some tweaking with the dead handy barrel adjuster and the Low stop it's ok on the big ring in anything other than the two highest gears, no bad thing, but rubs on the smaller ring, seems to me there's some lateral play in the rotation causing it, it's been ridden a few times service coming up soon ...
     
  4. ianrauk

    ianrauk Tattooed Beat Messiah Staff Member

    Location:
    Barmy in Barming
  5. Chris James

    Chris James Über Member

    Location:
    Huddersfield
    Not sure if I understand the OP correctly. Does it rub when you are in the largest chain ring at the front and the smallest cog at the back? If so, don't use this combination! I don't know if there is a trim function on Tiagra shifters but in any case the chain line in the above situation is terrible and it should be avoided on principle.
     
  6. softpeadals

    softpeadals New Member

    Think you are mixing your combinations up here Chris.
    What should be avoided is running big front ring with the biggest cogs at the back and vice versa i.e little front ring with the smallest cogs.
     
  7. craigwend

    craigwend Grimpeur des Holderness

  8. pbar

    pbar New Member

    I am right in thinking it's mainly the small cog and small cog combo that's best to avoid. I often use the large cog and large cog, otherwise I'm pedalling like a maniac at reasonable speeds.
     
  9. John the Monkey

    John the Monkey Frivolous Cyclist

    Location:
    Crewe
    There should be a combination from the small chainring that replicates that gearing though. My situation is slightly different, as the SCR2.0 comes with a compact triple, but largest front/largest back always rubs, however well set up the gears are.

    The gear inch chart on this page might help point you in the direction of an equivalent set of cogs.
     
  10. Chris James

    Chris James Über Member

    Location:
    Huddersfield

    Ooops, that is what I meant to write.
     
  11. OP
    OP
    Kestevan

    Kestevan Last of the Summer Winos

    Location:
    Holmfirth.
    It's not the chain run that's the problem. It's only an issue on the lowest possible gear (small front ring, largest rear). It's as though the return tension isn't enough to pull the front cage back far enough.

    I've checked the cable and all looks to be OK (no sticking I can detect, and the cable moves freely). The cage itself does appear to be sticking "somewhere" though.

    Thanks for the suggestions, I think I'll try stripping if down and thoroughly cleaning/lubing everything, and if that fails, take it to the LBS for a coat of looking at.
     
  12. Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    Do you know which bit's rubbing? If the deraileur is set to low, it might be rubbing on the top of the cage, in which case all the adjustment and cleaning in the world isn't going to help. Also is it straight i.e. parallel to the chainrings.
     
  13. Chris James

    Chris James Über Member

    Location:
    Huddersfield
    Now I understand you. Well, there are only three things you can adjust - the low stop position, the barrel adjuster on the downtube and lastly the cable clamp.

    Off the top of my head I can't remember if the front mech moves inwards or outwards with a tighter cable. If the former then pulling the slack out of the cable next to the downtube will demonstrate whether or not the stop is in the correct place.

    If the latter then adjusting the stop lower should result in the derailleur moving - if it does then there is sufficent tension in the mech.

    By the way, is it constant rubbing or cyclic - i.e. are your chain rings tightened fully?

    In general, the chainging between chian rings is achieved by the barrel adjuster. If the barrel adjuster is set so that it shifts okay then the rubbing in bottom gear should be eliminated by adjusting the low stop. If you cannot adjust the stop low enough to stop rubbing it may be that the cable was clamped in the wrong place - reclamp and start the process again. My first para should give you an idea if this is likely to be a problem before you start though.

    Don't want to sound rude but have you tried following the Shimano instructions (available via the internet if you have lost them)? Generally speaking Shimano's instructions are excellent.

    Apologies if you already know all this and it still doesn't work! In which case I suggest a visit to the bike shop.