Front derailleur woes

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  • First time building up a (geared) bike from scratch and I'm really struggling to get the FD working properly.

    First attempt resulted in not being able to shift up into the big ring, though I couldn't tell if this was because of a lack of tension, or because of poor alignment. The cable sounded like a bowstring, so I don't think it was a tension issue, but I'm obviously a novice.

    Leads me to alignment... I've got a braze on FD, mounted via a clamp on adapter. No matter how much I rotate or angle the adapter or the derailleur itself, I can't get the outer edge of the derailleur to sit 'over' the big ring. I THINK this might be causing my shifting issues, as the FD simply can't move far enough across? Do I need to try a different adapter? Fashion a little shim to shift everything 'out' more?

    That all said, I am able to manually push the FD with my hand from small to big ring whilst turning the cranks, albeit with a lot of chain rub, so maybe it IS aligned ok?!

    Tldr: do I actually need the derailleur aligned directly over the big ring? How much tension should there be in the cable when clamping in the small ring? What other obvious things might I be missing?!

  • Is the mech definitely compatible with the shifter?

    Is the chainset and BB (if not modern/hollowtech/pressfit) compatible with the mech?

    If so, definitely just upper limit.

    If not internal cable routing if you pull/tug on the cable, does it shift up to the big ring?

  • Yes, all compatible (same groupset throughout), including BB.

    So I don't need to worry too much about the derailleur sitting directly over the edge of the front ring? I guess I'm concerned that if its not set 'far enough out' to begin with, it'll never clear the big ring when shifting? But perhaps it doesn't need to?

  • Can you post a side-on picture of the FD/chainset set-up.

  • Use the adjustment screws to get the derailleur to sit over the larger cog. Just slacken them both right off then wind them in to dial it in to the right alignment.

    The other problem sounds like your cable is too tight. It doesn’t take much. Derailleurs usually rely on tiny adjustments to get it spot on.

  • Could have been that the cable was too tight - I was a bit clueless as to how taut it needs to be when in the small ring. I'm guessing now that so there's slack, but not tight, is the way to go?

    If helpful, I've added a couple of photos. You can probably see that i can't get the FD 'over' the big ring...

    2 Attachments

    • IMG_20200426_094010828.jpg
    • IMG_20200426_094045814_BURST000_COVER.jpg
  • The new Shimano mechs need quite a bit of cable tension to get them to shift properly. You'll need an inline barrel adjuster if there isn't one on the frame, unless you use the allen key trick.

    Easiest thing to do is disconnect the cable and just push the mech across by hand to see if it moves over to the big ring.

    Another thing to check is you've clamped the cable in the correct position at the mech.

  • The frame i’m about to buy has a braze on for bottles in the area where the fd-band would sit. Is there any way of finding the height a fd would sit in relation to the bb?

    The braze on was at approx 115mm c-c from the bb.

    The mech/crankset intended are grx600.

  • Shimano specify the FD cage being 1-3mm above the big ring normally, not sure if that's what you're asking?

    Or maybe if there's something in the way of where FD would go and it comes equipped with GRX it's 1x specific?

  • Yes i read the docs. Saying the cage was supposed to be this and that above the big ring. Then calculated the diameter of the intended 46t big ring. Then lookaed at images of the FD clamp to try and guess its vertical distance from the cage.
    I then decided that, well, it will probably work. Ill get one of those problem solver bolt on adapters with an adjustable slot. And if it doesnt work ill Just go 1x. :-)

  • Not sure if this is a single issue thread or it’s appropriate to have a moan about other FD woes in here. Anyway, SRAM Red 22 FD slipped on a ride yesterday and left me spinning in the granny gear all the way home. It never shifted as well as the Campagnolo FD’s I’ve had and I’m having an absolute nightmare getting it to work now. Followed step by steps twice and it still won’t shift into the big ring when I’ve finished. May be the first time ever I need to resort to an LBS service to get it working. TL;DR: Buy Campagnolo

  • Possibly a dumb guy follow up, but here goes...

    After getting more tension into the cable, surprise surprise, the FD now shifts nicely into the big ring. However, the issue now is that the chain rubs against the FD cage when I'm in the small(er) cogs. I've re-tensioned, adjusted the H limit and barrel adjuster, but no luck.

    I've convinced myself the issue is that I have a braze on adapter which doesn't 'reach' out far enough to set the FD in the right starting position (meaning the derailleur will never shift far enough out because it only has so many degrees of lateral travel).

    If that's the case, is it possible/sensible to 'shim' the adapter outwards by a couple of mm to set the derailleur in the right position? I even thought about a simple roll or two of electrical tape under the mount, but this seemed botch-y at best...

    Obviously the thing works, but the rattle/grind of chain on cage is frustrating!

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Front derailleur woes

Posted by Avatar for allsop @allsop