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Old 05-15-09, 11:20 AM   #1
TheFountain
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Chain STILL rubbing against Derailleur Cage

I've just adjusted both the rear and the front derailleur, but the chain keeps rubbing against the cage even though the I'm switching gears smoothly (minus the rubbing of course).

In gear 3, it rubs on the largest two rear wheel sprockets. In gear two it rubs on the middle 2 sprockets. And in 1st, it does not rub at all.

How can I fix this?
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Old 05-15-09, 11:53 AM   #2
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I've just adjusted both the rear and the front derailleur, but the chain keeps rubbing against the cage even though the I'm switching gears smoothly (minus the rubbing of course).

In gear 3, it rubs on the largest two rear wheel sprockets. In gear two it rubs on the middle 2 sprockets. And in 1st, it does not rub at all.

How can I fix this?
I'm confused. Your title says it's rubbing against the cage (I assume front). Your post says it's rubbing against the rear cogs ?!?!
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Old 05-15-09, 12:03 PM   #3
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I'm a bit confused about what's actually going on here because it sounds like you're dealing with two problems.

For the front derailleur, look down from the top and verify that the edge of the cage is parellel to the chainrings. Shift the chain to the largest cog in back and check that you can shift to each chainring. Shift chain to the smallest cog and repeat. If that's good then pedal and look for the point on the cage where the chain is rubbing. Turn you're cable barrel in or out 1/4 turn increments to alleviate the rub. If that doesn't work you may have to bend the cage slightly to resolve the problem.

For the rear derailleur, just make sure that you H and L limits are set according to the manufacturer and then check that you can shift up and down the cogs smoothly. If so you should be good to go. I don't know if it's normal for a chain to rub on adjacent cogs but if it's only slight contact I wouldn't worry about it.

Mike
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Old 05-15-09, 12:04 PM   #4
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Sorry, no. It's rubbing against the front derailleur cage. Only in those specific cogs.
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Old 05-15-09, 12:09 PM   #5
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Ahhhh, is it only doing it in the stand or while riding. My MTB will rub the cage slightly when I'm in the middle chainring and large cog while it's in the stand but as soon as I ride it the rub stops. Also, if you're in the big chainring and rubbing the cage when the chain is on the two or even three largest cogs that's kind of expected as you're pretty badly crosschained at that point. For the middle chainring I would only expect you to have a rub when you're in the smallest cogs. Same thing for the small chainring.
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Old 05-15-09, 12:27 PM   #6
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You need to adjust the front derailleur a tiny bit ("trim") as you shift the rear to avoid the rubbing. As you shift the rear, then chain moves left to right inside the front cage and will rub when in the extreme gears in the back. No way around it.... unless you get the new electronic Dura-Ace which I hear does the trim automatically.
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Old 05-15-09, 02:13 PM   #7
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You need to adjust the front derailleur a tiny bit ("trim") as you shift the rear to avoid the rubbing. As you shift the rear, then chain moves left to right inside the front cage and will rub when in the extreme gears in the back. No way around it.... unless you get the new electronic Dura-Ace which I hear does the trim automatically.
How do I adjust it as I shift? While riding?
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Old 05-15-09, 02:21 PM   #8
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How do I adjust it as I shift? While riding?
Your front derailleur shifter/brifter already has this functionality.

Read the documentation that came with it or have a look at the Shimano tech docs site: http://techdocs.shimano.com

Example of a 105 brifter: http://techdocs.shimano.com/media/te...9830621374.pdf
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Old 05-15-09, 02:26 PM   #9
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depends on the shifter. some have trim, others do not.

DT and bar-end friction shifters have infinite trim.
shimano road STI, depending on model, have trim where it allows you to have another indexed position between the 3 indexes. (some of the low end STI levers do not have it.)
campagnolo escape does not have trim
campagnolo 2009 levers have a lot of indexed positions giving you plenty of trim.
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Old 05-15-09, 02:59 PM   #10
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I'm not sure if it's trim that he's dealing with here. If the chain is rubbing the cage when he's on the large cogs then something else is at work here. The trim function comes into play when you get down to the smaller cogs.
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Old 05-15-09, 04:49 PM   #11
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Problems with front-derailleurs are usually best solved by removing the FD and re-installing it from scratch - checking that it's outer-cage is in the same plane as the front chainrings, and properly trim with a distance of 1 - 2mm* height over the outer chainring during the shift. Here are two sets of directions to install a FD, video and written with illustrations:

http://bicycletutor.com/adjust-front-derailer/

http://www.parktool.com/repair/readhowto.asp?id=75

And sometimes certain combinations are destined to rub - here's a set of Shimano illustrations showing this:

http://i424.photobucket.com/albums/p...malFD-M961.jpg
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Old 05-15-09, 07:04 PM   #12
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I'm not sure if it's trim that he's dealing with here. If the chain is rubbing the cage when he's on the large cogs then something else is at work here. The trim function comes into play when you get down to the smaller cogs.
Wrong. The chain can rub on either side of the cage depending on what back gear you're in, so trim adjustments often need to be made in either direction.

To "trim" means to shift your front derailleur a little bit to move the cage away from the chain to stop the rubbing. Some front shifters have no trim option (so I've heard, but can't understand why). My Campy Chorus shifter has multiple clicks, so I can either shift between front chainrings using all the clicks, or just shift a click or 2 to avoid the rubbing. This is one of those things that is 50 times harder to explain than to do.

Old style friction (non-indexed) shifters had no clicks, so you were not limited in your trim options.
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