Bicycle Mechanics - Front Derailleur fun: Can't seem to keep chain off of cage
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Last night I decided to give my new bike a tune up as it was shifting slowly and the front cage was rubbing against the chain. It's a 21 speed Hybrid bike with Shimano indexed shifters. The rear derailleur adjustment went beautifully but the front derailleur... not so much. After adjusting it (lowering and changing angle) its better but second gear rubs badly on gears 1, 2, 6, & 7. If I get it to clear one side it messes something up on gear 1 or 3 usually. Most of the rubbing seems to be on the inner front part of the cage with some rubbing on the outer half of the cage when in gears 6 & 7. Is this a sign of the angle being off or is the front derailleur on my bike junk (my bike is a lower-middle end $300 model, so it's Shimano but I assume low end Shimano)? Also I assume that second gear should be able to reach gears 2-6 if not all of them... is that an incorrect assumption?
I just read this guide (http://www.parktool.com/blog/repair-help/front-derailleur-adjustments) and I think my derailleur might be adjusted in a little too much but I haven't been near the bike to check, since finding that guide.
Any advice is appreciated,
03-12-11, 01:46 PM
BB bearings adjusted for no play?
It's a new bike and everything is pretty solid but it's worth a shot to check. Do I try to slide the cranks back and forth to check for play?
03-12-11, 02:25 PM
I set the front deraileur so that there is no more than 2mm clearance between the outer chain ring and the bottom of the front deraileur cage with the outer cage plate parallel to he outer ring, tip to tip as some deraileurs are slightly concave. With the chain on the middle chain ring and in 7th gear adjust the front cable tension, tighter or loosen until the chain is no longer rubbing on the outer cage plate, within a millimeter or less on the middle ring. Then check the travel limits. You should be able to shift into the inner ring in 7th gear and adjust this in as far as you can but then check to make sure it will down shift in the lower gears in back but might have to let it back out slightly so it doesn't rub in lowest gear. Then check outer ring adjust so it doesn't over shift or rub in high gear. If you need more help go to Park Tool.com
You've described the problem perfectly and it may not be a problem at all. The angle the chain comes to the chainrings from depends on which rear sprocket it's coming from. If the cage is perfectly centered, a chain coming from outer rear sprockets may rub the outside, and one coming from inner sprockets rubs the inside.
With a bit of fussing you may find a trim that doesn't rub with more sprockets, but I doubt you'll ever be able to get all of them.
Many shifting systems allow you to trim the front derailleur slightly to correct for that while riding, but many don't. Check your shifter and see if there's a second click spaced very close to the one for the middle for trimming, but if not you'll just have to set it to not rub on the combinations you ride in the most.
03-12-11, 02:43 PM
It best to use only 3 to 4 gears in the back for every one in the front . like 1 (Smallest )in the front then 7,6,5, maybe 4 in the back, 2 (middle ) in the front ,goes with 6,5,4,3 and with the 1 ( biggest) in the front maybe 4 ,then 3,2,1 . this cut down on cross-cogging and save on the parts like the chain.
Thanks for the suggestions, I'll give them a shot. I mostly would like to be able to use 2-7 (33-14) so I can practice spinning while on road. Off road I usually jump from 2-5 to 3-5 for the sake of shifting efficiency.
03-12-11, 05:38 PM
Try this I am sure it will help.
Which shifters do you have, model number and name?
I'd have to double check but the front Derailleur looks like the Shimano 105 (except mine is a bolt on) they have on Nashbar. I'd have to double check the shifters.
Using the links posted I was able to get everything working. Then going on a single track mountain bike trail I decided to wreck in spectacular fashion and kicked my front derailleur and now I have to adjust it again ;). In the future I'll probably replace it with a heavier duty model as it looks like we're going to do more single track stuff.
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