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Old 11-08-10, 05:32 PM   #1
shrp71
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Front derailleur adjustment, chain rub

Hi all,

I'm having some trouble with chain rubbing on the front derailleur of my hybrid and can't seem to figure out what's wrong. I've followed just about every bit of info I've come across on the web, including the Park Tool guide and Sheldon Brown's site, to no avail.

In the middle ring up front, the chain will either rub the inside cage when in low gear in the rear (1-2, large cogs) or rub the outside cage when in high gear in the rear (7, small cog). I can't seem to find the right amount of cable tension so that there is no rubbing at all while in the middle ring. I can tighten to get rid of the rub in high gear, but then I have rub in the lower gears and vice versa.

I've positioned the height so the cage just clears the teeth of the large ring and set the angle so the chain looks parallel to the cage from above. I've adjusted the low limit screw with the cable slack and the high limit screw with a good amount of cable tension so that I can shift smoothly between rings without the chain falling off or getting stuck, but then I end up with rub in the middle ring.

One thing I've noticed is when adjusting the low limit screw, I can't get it so the chain is as close to the inner cage as possible without it being too tight and not letting me shift down to the small ring. So there is a sizable gap between the chain and the inner cage in the lowest gear that I suspect may be leading to the rub in the middle ring and higher gears.

This is a new bike (bought earlier this year), so it's not a problem of worn-out components. I really can't afford to have it adjusted at a bike shop and would prefer to do it on my own, so any insights are appreciated. Thanks.
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Old 11-08-10, 05:48 PM   #2
Al1943
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Quote:
Originally Posted by shrp71 View Post
One thing I've noticed is when adjusting the low limit screw, I can't get it so the chain is as close to the inner cage as possible without it being too tight and not letting me shift down to the small ring. So there is a sizable gap between the chain and the inner cage in the lowest gear that I suspect may be leading to the rub in the middle ring and higher gears.
This sounds as if there may be too much tension on the cable.
Also, be sure the chain is on the smallest chainring and largest rear cog when setting the low limit screw.
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Old 11-08-10, 06:06 PM   #3
shrp71
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Thanks for the reply. I don't think I described my adjustments clearly. I have been adjusting the low limit screw with the chain in the lowest gears (small front, large rear) and with the cable completely slack. However, if I adjust the screw so that the chain just barely touches the inner cage, when the cable has been re-tightened to the appropriate tension and I've switched up to the middle ring, it won't let me shift back down to the small ring because the screw is too tight. Thus, I must loosen the L screw in order to be able to shift down to the small ring, but this leaves a bigger gap between the chain and the inner cage which I think may be accounting for the rub when the chain is in the middle ring and high gears.
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Old 11-08-10, 06:19 PM   #4
bkaapcke
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If your FD has a screw holding the cage plates at back of the cage together, remove the screw and put a small washer between the plates. This will widen the rear of the cage and may give you the room you need. There may already be a washer under the head of the screw you can use. bk
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Old 11-08-10, 09:52 PM   #5
cobba
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You might find some useful info on the following link: http://bicycletutor.com/guide/
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