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Front derailleur rub chain when on innermost/smallest cog and rear derailleur is on innermost/largest cog.

I have watched Park tools guide to adjust both derailleurs and tuned the gears to make them work well. Though my barrel adjuster on front derailleur is busted.

My front L limit screw is also quite tight to screw it in and I think it is way outwards. So I think because of this I don't see much movement in front derailleur. Though shifting on front cogs is good and only issue is shifter gets slight stiff when pushing it to smallest front cog.

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Criggie
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Iwantroca
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  • So you want to move the front derailleur more inwards (to prevent it rubbing on the chain in the smallest chainring + biggest cog combination)? Your cable is already slack and the limit screw not making contact but it’s still not enough? – Michael Jan 22 '22 at 11:59
  • Yes you got it right. Have you also checked the pics I uploaded on imgur? I have uploaded a pic of me stretching the cable and also the pic of limit screws. – Iwantroca Jan 22 '22 at 12:09
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    I guess it’s fundamentally some kind of chainline issue where you’d actually need a wider buttom bracket or spindle, but I don’t know enough about this kind of thing to risk writing an incorrect Answer ;) However, maybe it’s enough to open the front derailleur’s clamp and rotate it slightly inwards? If it’s rubbing very lightly (and only in that gear which you probably don’t use that often) I guess you could also just ignore it. – Michael Jan 22 '22 at 15:57
  • After seeing the pics: There's still a bit left in the 'L' screw. And a tiny bit of misalignment (clockwise from top) may be permitted if shifting is not affected, as @Michael suggests. – Carel Jan 22 '22 at 19:08
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    Frankly triples are often like this. There may not be a perfect spot - it could be a matter of choosing between some rattle in the low-low gears or the highest gears. Personally I set my road bike triple up so the hard/high gears are silent, and I accept some chain rattle in the grannie gear. – Criggie Jan 22 '22 at 21:00
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    If your comment were an answer @criggie, I should be delighted to up-vote it. – gschenk Jan 22 '22 at 21:13
  • @Criggie I agree. Chain velocity is lower in easiest gear combo, so rubbing there is preferable to rubbing in the fastest gear where the chain velocity is really high. – MaplePanda Jan 23 '22 at 07:56
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    What's wrong with your barrel adjuster? They are a very cheap part to replace if needed. – MaplePanda Jan 23 '22 at 07:56
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    @MaplePanda Blind guess - the threads have been stripped in the housing that hold the barrel ? – Criggie Jan 23 '22 at 10:20
  • @MaplePanda threads on my shifter are busted. My whole left shifter is kinda defected since I bought it, also cannot open its screws. But since I bought it online. – Iwantroca Jan 23 '22 at 14:49

1 Answers1

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I can't speak to the driveline point - if your bike has the original crankset and original BB then its probably correct.

My method for front derailleurs is something like:

  1. Set the height of the mech so that at maximum reach it clears the big chainring by 1~2 millimetres.
  2. Set the rotation of the mech so the cage is parallel to the chainrings.
  3. Then I set the high and low stops by eye.
  4. Finally I set the shifter cable and with indexed shifting I focus on the big chainring.

After this it gets less "method" and more "iterative" Personally I ride in the big ring mostly, so I set that up to have no chain rub at in any rear gear choice and accept the grannie will rattle a bit. But if I'm in the grannie then I'm probably climbing something steep, and most of the bad noises will be coming from the rider :)

Note that derailleur cages are relatively easily bent by impact. Additionally, some derailleurs need to be rotated so their tail end is subtly in-board and thus the cage is not parallel to the chainring.

Front mechs can be very faffy. One thing that makes it easier is when the whole area is clean, so degrease and clean the chainrings, shifter, cassette, rear derailleur, and chain. Try to elevate the bike too - working with the rear wheel on the ground is no fun.

Your limit screws are not at their own limits - they can be backed out till the thread inside is flush with the inside of the metal, and can be screwed in till the head bottoms out. If they're stiff, consider adding some oil like CRC or WD40 to get them moving, but also consider they need to be stiff to not back out under pressure. Just ensure your screwdriver tip is a good fit, and that you don't camm out the screw head.

Criggie
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  • Yes big chainring is more important for me as well. So now that I have tuned it well, I am bit hesitant to fiddle randomly for the least used gear combination. And as you can see in first pic (lowest chainring to highest sprocket setting), my L limit screw is forced to be bit outwards by some black piece inside derailleur so I cannot screw it in fully. Is this might be because of high wire tension? – Iwantroca Jan 23 '22 at 11:27