Bicycle Mechanics - Derailleur help
Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.
06-10-09, 04:28 AM
1) I noticed that my chain is rubbing against the front derailleur cage when I'm on the largest & smallest cog + smallest chainring (on a double), as well as all the combinations on the largest chainring.
I've fooled around w/ the front derailleur's (Ultegra) limit screws (which are not labelled so I'm not sure which is the low and high...) and I noticed that I could get it to not rub while on Largest Cog + Small Chainring, but then it would still rub when on a higher gear.
I'm sure that the cage is aligned properly, and it's at an appropriate height.
Any tips on how to adjust my front derailleur to stop the rubbing?
2) While adjusting the rear derailleur it still occasionally skips (both up and down) one gear around the middle of the cassette. How can I remedy this? I've been messing around and I think I'm making it worse, and I'm at the point where it's just frustrating.
Of course, I could always bring it to a shop and get them to fix it, but I'd rather save the money and try to learn to do it myself.
06-10-09, 04:53 AM
As long as I'm reading this correctly . . .
You are cross-chaining, or at least partially.
Make sure (with limit screws) that the front der. doesn't rub in these combos:
small (chainring) / big (cog) and big (chainring) / small (cog)
From there . . .
If you get rub towards the last few cogs (in either direction) that means you should either trim the FD or switch chainrings. For example, if you hit an incline go down to the small chainring and then find the right cog in the back, instead of trying to hit the biggest cog in the back while still on the big chainring, and vice versa.
On 2, sounds like too much tension in the der wire, screw in your barrell adjusters, and start from the beginning. Check this out . . . http://bicycletutor.com/adjust-rear-derailleur/ and go from there
06-10-09, 05:36 AM
Some combinations are going to rub regardless. At least that's the gist of what Shimano is trying to get across in this enclosure that comes with their derailleurs. This isn't very clear, but...
If you're riding with a Shimano indexing front derailleur, adjust the limits for effective shifting and optimum position in the gear combinations you expect to ride in, usually the mid to outer cassette cogs on the outer, and mid to inner cassette cogs on the inner.
The cage should be wide enough to accomodate most combinations without rubbing, but will rub on highly crossed combinations when the chain comes at an extreme angle. Not an issue, since crossed combinations are more inefficient and should be avoided.
If you're riding a system that allows the FD to be trimmed, (Campy, Sram) set the limits for good shifting and trim using the outer/outer & inner/inner combinations, then use the ability to trim to eliminate chain rub if and when it occurs.
06-10-09, 07:14 PM
Just the minor cable-stretch, once you have torqued-down the pinch-bolt holding the cable to the FD*, is enough to make the FD rub where it wasn't before. I find this especially true with triples. Then you can either release the pinch-bolt and yank the cable tighter again - which is likely to cause fraying and generally compromise your new cable. Or you can do what I just did with a triple/cable set-up that was driving me nuts.
I installed a barrel-adjuster on the cable.. A 1/4 turn solves the problem, or thereabouts.
* Usual recommended torque is 48 - 60psi.
06-10-09, 08:57 PM
On an ultegra front derailleur you should be able to eliminate the rub on large chainring, smallest cog. Follow the F.D adjustment proceudre on parktool, and report the results. Hell, i've gotten extremely acceptable front shifting on a piece of **** Shimano C101 front derailleur on a piece of crap generic triple crankset with nary extra work.
Use the instructions at the Parktool site offered above by operator. Do each step in proper sequence leaving nothing out.
Powered by vBulletin® Version 4.1.12 Copyright © 2013 vBulletin Solutions, Inc. All rights reserved.