Bicycle Mechanics - Chain moving between front sprockets, falling off

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.



PDA
carsick
05-08-04, 06:58 PM
I bought a used Trek 2120 road bike and just started riding it lately. I had the chain fall off the front sprockets, both the large and small sprockets. This happened four times today on my first long ride (14 miles). I also had a sitituation where the chain jumped between the small sprocket and the middle sprocket about 4-5 times in about a 10 second time frame (without using the shifters).

I assume there are limit adjusters on the front derailer to take care of the first problem, but am wondering if the sprockets are warped which is causing all my chain problems. Or could it be bottom bracket bearings/sloppiness?? Any advice appreciated. Thank you.

RegularGuy
05-08-04, 07:17 PM
There are indeed limit adjuster screws on the front derailleur that can prevent the chain from falling off. You can do the job with a screwdriver and some patience. By the way, if the chain faills off of the large chainring, you can usually pedal and shift it back on without stopping.

There are good directions for adjusting the front derailleur limit screws here:

http://www.bikeforums.net/barnettes/barnetts_ch33.pdf

and here:

http://www.parktool.com/repair_help/howfix_frontderailleur.shtml

I don't know how mechanically adept you are. There are a number of possible causes for the "auto-shifting" you're experiencing. A worn chain, or worn cogs, or both are likely culprits. It might also be a stretched cable. I'd suggest going down to your local bike shop and having the mechanic look it over.