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Chain rub front derailler Shimano 9 speed STI(2 posts)

Chain rub front derailler Shimano 9 speed STIkomatiite
Apr 10, 2003 4:07 PM
hey all. ive got Shimano 9speed TRIPLE 105 components and for some reason i cannot get my front derailler adjusted for anything. just when i think that ive got it, it starts rubbing on the derailler. I cant tell if its the inside or outside of the derailler. the remedy? if i act like im switching up to the big ring on the front it goes away. im only talking like a 1//4" and then the rubbing goes away.

this is REALLY annoying. after i adjust it: big cog on rear, small ring up front, retighten der. cable and leave lots of play in the fine adjustment on cable its fine UNTIL i switch to big ring for a while. Now, when i switch down to middle ring and really apply a lot of pressure on my pedal stoke, it starts to rub. (I have it setup so that there are two index shifts on the middle cog.)

I have tried countless time to fix this and its probably something really small that i am overlooking. Any help with would be GREATLY appreciated.
How is it possible you can't tell which side the chain rubs?Kerry
Apr 10, 2003 5:28 PM
Your derailleur cage is quite wide - you should be able to tell visually whether the chain is rubbing on the inside or outside. 1/4" of cage movement is huge. While you may tweak a bit from this, the outer cage of the derailleur should be parallel to the chainrings. This is a starting point, and you may find things work better with the cage slightly pivoted outward at the rear. The derailleur should be positioned vertically so that you have about 1mm clearance above the large chain ring (nearly touching!). The upper limit screw should be set so that the cage is just beyond rubbing the chain when in the large chainring and smallest cog. The lower limit screw should be adjusted so the cage is just beyond rubbing the chain when in the small chainring and largest cog. The cable should be clamped on the derailleur with the shifter indexed all the way "down" (like shifting to the small chainring), the barrel adjuster all the way in, and the chain on the small chainring (this is because you can't remove all the cable slack during clamping, and you will end up turning the barrel adjuster "out" to remove that little bit of slack). Shift through the gears and look for both shifting quality and chain rub. If the derailleur shifts "slow" to larger rings, turn the barrel adjuster out. If it is slow in shifting to smaller rings, turn the adjuster in. If the chain rubs on the outer plate while on any given chainring, turn the adjuster out. If the chain rubs on the inner plate, turn the adjuster in. You should be able to get good adjustment unless you have a system problem. Simply looking at the front derailleur/chain relationship after each shift should guide you to the next step. Your upper and lower limit screws may need slight adjustment after riding a bit to eliminate rub, to improve shifting in certain gears, or to prevent the chain from over shifting the big ring or dropping off the small ring.