I just purchased a 2012 Rumblefish Pro, which comes with Deore XT 780 shifters, with the left shifter having the 2 or 3 mode adjustability for the front derailleur. My FD is the new Dyna Sys model that came set up with the new triple crank, of course. I decided that I don't need the large chainring so I put a Shimano bashguard special ordered from my LBS in its place. Then I set the shifter to the 2x mode position. My first problem was when I broke part of the head off the slotted plastic screw because I had attempted to turn it while the shifter was in the lowest position. Be careful, it is a very flimsy screw and IMO it should be made of metal. However, I was still able to get my screwdriver to turn it once I shifted to the middle position. Anyway, after resetting my cable because in the 2x mode the shifter actually uses the 2nd and 3rd chainring positions, not 1st and 2nd like I had assumed, I was never able to get proper shifting. No matter what derailleur adjustments I would make, I would get unacceptable rubbing on either inner or outer plate and hesitant or incapable shifts from either low to high or high to low. Adjusting derailleur height did not help either. So, I switched the mode back to 3x, reset the cable and immediately my shifting was restored. I can't help but conclude that either the distance from index 1 to 2 is greater than from 2 to 3 - I couldn't tell by eye, or that the design of the chain interface between these new 24-32-42 chainrings is somewhat different between 1 to 2 and 2 to 3. Or maybe that Shimano assumes you will use a larger chainring set in the 2 mode case, as in a road set. I have no issue having a potential 3rd shift onto the bash guard, I'll just be careful not to do that. Also, I found that I could lower the derailleur now that the outer chaing ring isn't present and get even better shifting performance from 1 to 2 and vice versa than when I had the triple set up. I would really like to hear anyone else's comments on what I found. In sum, this was a very aggravating experience but now I'm happy with my 2 by 10 setup.
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