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Front Derailleur Problems(3 posts)

Front Derailleur Problemspkompath
Sep 19, 2002 6:53 PM
I own an early Giant Perigree and recently replaced the Biopace cranks and chainrings with 105s. However, after numerous raising and lowering of the existing Exage der. I havent been able to shift properly or not at all. Mainly, the problem is from the small to big. So, any clues, suggestions, etc on how I can make it work or just forget about it.
My other option is to purchase a 105 der., but then again, it might not be the der. Im willing to take that chance.
Thus, on an older steel bike, what is the seat tube diameter?
Did you change bottom brackets?Spoke Wrench
Sep 20, 2002 4:22 AM
If you didn't, my guess is that your chainrings are spaced farther from the seat tube than previously. I think that's likely the case because bottom bracket spindle lengths have been gradually declining through the years.

If that is the case, the "A" solution would be to buy a bottom bracket that will space your smallest chainring about 5mm from your chainstay. The "B" solution would be to readjust the limit screws on your derailleur to match your new spacing. You probably should readjust your cable too. If it was my bike, I'd probably do "B" just to minimize the expense on a bike this old.

I really doubt the problem is your derailleur unless your crank is so far out that it just runs out of range. Most any front derailleur should do the job with a friction shifter. Your front shifting should be significantly improved with the round chainrings.
Some thoughtsKerry
Sep 20, 2002 4:35 PM
The outer cage of the derailleur should be parallel with the large chain ring - sometimes shifting will improve a bit if the lower part of the cage (toward the back of the bike) is just a bit closer to the crank. The travel limit screw should be set so that the derailleur moves only far enough to get a good shift - too far and you can shift off the large ring. If the derailleur can't be adjusted so that the cage goes out far enough, then your BB axle is too long. The derailleur cage should (vertically) clear the large chain ring by 1 mm (not very much). The cage should not be bent or dented. With the shifting pins on the 105 rings, you should not be having this problem unless the derailleur mechanism has gotten so loose that it will no longer do the job. You may be starting down an upgrade path that could teach you why it's not wise to upgrade old bikes.