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Old 08-01-08, 08:11 PM   #1
cooleric1234
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Front derailleur won't go in enough

I'm doing my first real climb tomorrow and I noticed my front derailleur rubs on the chain when I'm in the smallest chainring in front (triple) and largest cog in back. I tried adjusting the set screw, without any tension on the cable. The problem is that when I adjust it as far as it goes towards the seat post it still rubs. I can't slacken the cable any more and adjusting the screw no longer moves the derailleur. How can I get it to move in more? Do I have to bend it? Is the bottom bracket spindle too short? Is there anything I can do to move the derailleur in more and eliminate the rubbing? The quicker the advice the better as I'd like to adjust it before early tomorrow morning. Thank you.
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Old 08-01-08, 08:24 PM   #2
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The derailleur and crankset are probably optimised for different chainlines. If you can get a decent chainline, then swap your BB out for something shorter.
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Old 08-01-08, 08:35 PM   #3
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1. Check the derailleur height. A dime should fit between the large chainring and the cage in the large ring
2. Check the "tail" position. Is it in line with the rings, or pointed outwards? If it's outwards it can rub like you describe.

If neither of these is a problem, then it may not be something you can fix by tomorrrow morning. Use the 2nd largest cog
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Old 08-02-08, 08:35 AM   #4
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Originally Posted by orangepaint View Post
The derailleur and crankset are probably optimised for different chainlines. If you can get a decent chainline, then swap your BB out for something shorter.
Uh, no. If the front derailleur is hitting the seat tube before the cage clears the chain properly, the OP needs a longer bottom bracket spindle. The crank needs to be further away from the frame.

In fact, Campy used to recommend two different bottom brackets for it's cranks depending on the seat tube diameter. A 35 mm seat tube required a longer bb.
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Old 08-02-08, 01:11 PM   #5
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Originally Posted by Bob Barker View Post
2. Check the "tail" position. Is it in line with the rings, or pointed outwards? If it's outwards it can rub like you describe.

If neither of these is a problem, then it may not be something you can fix by tomorrrow morning. Use the 2nd largest cog
I tried the first suggestion by rotating the clamp a little bit inward. It seemed to work on the bike stand, but then when I went riding the problem seemed even worse. (Side note, it seems that happens quite frequently to me, once I put weight on the crankarms all the fine adjustments change slightly...is that okay?).

I did end up using the 2nd cog, but later in the ride it sounded like that was rubbing too. I suppose I might have to go with a longer BB. I usually don't use that low of gearing, so it's never been an issue.
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Old 08-02-08, 02:41 PM   #6
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Originally Posted by cooleric1234 View Post
I can't slacken the cable any more and adjusting the screw no longer moves the derailleur. How can I get it to move in more?
Have you always had this problem or is it a new problem?
With the shifter in its lowest position is there any slack in the cable?
Have you tried releasing the cable from the derailleur at the pinch bolt?

Al
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Old 08-02-08, 04:37 PM   #7
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Yeah, have you unbolted the cable from the FD and pushed it back towards the lever?

I usually don't bother with the inner limit-screw and just use the stop on the shift-lever to dictate the inner position. However, sometimes the cable ends up a little too tight and I have to let it back out some.
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Old 08-02-08, 08:55 PM   #8
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I should have specified this in the original post better. The cable is totally slackened. I turned the barrel adjuster to the point where there was considerable slack in the cable, but I still can't get the derailleur to move in further. The limit screw moves it in to a point, then it does nothing. It's maybe a millimeter or two from where it needs to be. I've read maybe putting a spacer in the bottom bracket can work (not sure what that is). I've also read of putting a washer in the bolt holding the two sides of the derailleur together (it's a Tiagra derailleur).
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Old 08-08-08, 07:43 PM   #9
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I'm no expert but I would imagine that you should start at square one with proper textbook cable installation and adjustment by the book. I wouldn't think you would need any new parts of modification. You might benefit from taking it an experienced bike shop, you know someone who does this exact thing day in and day out. My local shop ... these two guys ... they're amazing, with fantastic technique. Truly experts in their field with the skill and dexterity to get any job done within minutes.
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Old 08-09-08, 02:13 PM   #10
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Cheque your chainline. Measure from the centre of the of the seat-post to the centre of the middle-ring. This should be between 42-45mm. If it's smaller than this, you need a longer BB-spindle.

Also make sure the rotation of the FD is correct. If the rear of the FD sticks too far outwards, the inner cage won't be far in enough to prevent rubbing.
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