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My bicycle is a Rockrider 520. I have replaced my front derailleur with Shimano Acera FD-M390 and my crankset with Shimano Acera FC-M391. But chain is rubbing inside of FD even when FD cable is not attached. I tried completely loose L screw but it still rubbing and FD is not moving inside anymore. FD is parallel with chainrings and there is 3 mm gap with FD and biggest chainring. How can I solve this?

Pics: http://imgur.com/a/QJlHg

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  • Did you change the front deraileurier because the old one was rubbing? Perhaps the front chainring is not flat? – Criggie Sep 6 '15 at 8:42
  • @Criggie The old one was a Tourney and it was shifting really poorly. And my old chainring was not flat. This one is very nice. – gkon Sep 6 '15 at 9:48
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    I've rarely found that the best position for the FD is exactly parallel to the rings. – Daniel R Hicks Sep 6 '15 at 11:47
  • When you were installing the derailleur and still had the Pro-Set Alignment Block on it were you able to align the derailleur with the largest chainring as described in Shimano's documentation: The level section of the chain guide outer plate should be directly above and parallel to the largest chainring. or did you see the same misalignment with the chainrings even at that point in the installation process? – Glenn Stevens Sep 7 '15 at 4:08
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You can:

  • lower the front dérailleur, so that the protruding part on the inner side of front dérailleur does not touch the chain.

  • if the above does not fix, try to re-align the rotation of front derailleur: make it just enough so that it won't rub on the lowest gear

  • then check if it rubs the chain on the highest gear, i.e. 3 -9 gear. If it does, try to adjust the cable so that it can bring the front dérailleur a bit further away on higest gear.

If all fails, it's now a trial and error from all the steps I have said.

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It might sound weird, but if you're finding trouble adjusting the FD on the lowest gear, try adjusting the high (H) screw. You'd be surprised just how much those two screws affect each individual gear. Unfortunately, these kind of adjustments are ones you really just have to play with until they're just right.

As for the initial rubbing, don't be surprised if you can't totally get rid of it. With certain group sets, (particularly Shimano, for some reason), the rubbing is still going to be there no matter how much adjusting you do.

You can try to prevent the rubbing by making sure your chain and drive train are kept clean and well lubricated.

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  • I think that a 3mm gap is quite big. 1-2mm are fairly enough. As for setting the FD parallel to the rings: Some MTB-FD are wider at the rear end than at the front. If yours in that case set the (thought) middle parallel to the ring. – Carel Sep 6 '15 at 8:37
  • @Weirix Like I said, the cable is not even attached. So I know that the position of FD is must be maximum inside in this situation (L is loosened completely). But it's not inside enough. I don't think there is a problem with H or L screws. And there is not a slight rubbing. There is a massive rubbing. I read somewhere that the axle length differ on cranksets. What do you think about that? I didn't changed that and my old FD is also not fit on the new crankset. – gkon Sep 6 '15 at 10:30

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