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STI puzzle - help an ageing ignoramus...

(7 posts)
  • Started 12 years ago by Its_Me_Knees
  • Latest reply from Its_Me_Knees
  • This topic is resolved

  1. Its_Me_Knees
    Member

    So then.. I got a new bike that has drop bars and STI shifters. Don't have the exact type to hand, but they use the separate wee lever (ie. not fully integrated into the brake lever) to move the gears in the 'sprung' direction, and a sideways movement of the brake levers themselves to do the work against the derailleur spring. Never used STIs before, and that may be a factor in what follows...

    The rear derailleur works fine, but the front one won't budge off the big cog. I'm scared rigid of forcing something in case it breaks, but I'm wondering if I've missing something obvious, like, for example, a transit screw or somesuch that stops a lever, or the mechanism itself, from moving.

    Any ideas what the problem might be, what to check, etc,etc? Don't be afraid to point out potential idiocy on my part - I'm new to all this stuff and I am perfectly capable of doing something very dumb (or even failing to do something that should be obvious...).

    All advice gratefully received :-) If push comes to shove I'll take it back to the shop but they're shut tomorrow and I was hoping to have a cobweb-clearing run out on the new steed, hence my appeal to CCE.

    Posted 12 years ago #
  2. kaputnik
    Moderator

    Sound like Sora or the model below (3200?).

    You release the cable tension on the front derailleur by pressing the thumb switch to shift - the spring in the derailleur does the rest of the work by pushing it left. The cable holds it in high gear the rest of the time.

    2 things can stop it moving across. The most likely is that there's actually too much tension in the cable so that it can't do the little bit of tensioning required to get past the ratchet that holds it in high gear. If you can't get past that because it's too tight, there's no way to let the cable tension out and shift across. You can solve this by undoing a bit of the tension in the in-line adjuster, which depending on age / model will either be where the cable exits the STI or more likely on the brazeon on the downtube of the frame where the gear cable and outer are held. Failing that, undo the cable from the derailleur clamp completely and give it a little bit more slack before tightening it all back together.

    Less likely is that there's something up with the limit screws (the 2 screws on the derailleur body, normally with the H and L by them). These press on the chassis of the derailleur depending on how far in/out you turn them and limit how far the arm can move left or right. Try loosening off the L one.

    Oh and third thing jumps to mind. There's sometimes a wee bit of plastic inbetween derailleur and chain to help in setting up? Check it's not still in there.

    Hope that makes sense? Basically sounds like there's too much tension in there, let a bit out. If it's Shimano all the technical instructions are available as PDFs on their website (techdocs.shimano.com). And you're right not to force it.

    Posted 12 years ago #
  3. wingpig
    Member

    When my Sora front mech was new it had a wee bit of plastic sort of Jammed into the parallelogram rather than between mech and chain...

    Posted 12 years ago #
  4. remberbuck
    Member

    Don't worry - I'll guess your bike will be just fine. For some reason - because they have further to travel? - I have always found that front derailleurs take a bit more effort than rear, and you have to wait that bit longer for the transition.

    One simple thought. Are you pressing the right way? The "seperate wee lever" suggests above Sora to me. If so, when you simultaneously push the brake and the lever for the rear derailleur then you move up. If you do the same for the front then the usual shop fitting will move you down. Simple reversion - but not always obvious.

    Try upending the bike and see what happens.

    And if all else fails, you can do most rides around here on the big cog. You'll just get there faster.

    Enjoy your day.

    Posted 12 years ago #
  5. Its_Me_Knees
    Member

    Thanks everyone - excellent feedback as ever. Model does indeed appear to be the Sora, so have downloaded the technical docs. Checked there was nothing obviously missing/wrong, and that there was no plastic block in the mech (also identified the odd bits of rubber that came with the bike as adjustment blocks for the levers). Re: tension - the small lever was indeed stiff (ie may have had difficulty clicking over the first ratchet point, as mentioned above) so mounted the bike on the repair stand and got the cogs spinning at a reasonable rate and... bingo! Lever was stiff but when pushed the chain plopped down a cog. Subsequent drop to smallest cog was much easier.

    So...tension issues sorted, uncertainties regarding blocks and rubber bits eliminated, and existence of new bike revealed to Mrs IMK (not as much flak as I had feared). A short outing around the locale...haven't ridden a 'racing bike' (as we called them back in the day) for about thirty years...what a difference! Very twitchy (presumably due to my lack of familiarity with the lightweight frame / thin tyres / carbon forks combination) and acceleration that genuinely surprised me (the bike may be lightweight but I certainly am not). Looking forward to a few more meaningful outings once I've got the hang of it...

    Posted 12 years ago #
  6. amir
    Member

    "existence of new bike revealed to Mrs IMK"

    You are a braver man than me!

    Posted 12 years ago #
  7. Its_Me_Knees
    Member

    @amir: Foolish, rather than brave. I think there will still be some sort of come-back. It's the waiting for it that kills you, though...

    Posted 12 years ago #

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