Rear Deraileur Troubleshooting
I thought I would ask about a problem my son is having with his rear deraileur. Bear with me, I am new to biking so I might use the wrong terminology.
Occasionally when in the high gear the chain pops off and wedges between the frame and gears. I adjusted the derailer and decided that is not "over shifting". I believe what is happening is the chain is bouncing off after hitting a big bump. It has never happened offroading (riding mostly in low gears), but on Greenways, he is often in high gears.
After some playing with it appears that the chain might be too long. But when I asked my dad how to remove a link or two, he mentioned that it could be the springs in the deraileur being warn out, no longer strong enough to put enough tension on the chain.
Oh, yea. The bike is a old 20" Trek with 1x6 gearing. The deraileur the factory Shimano SIS.
Your dad could be right. That sounds like a fairly old bike and springs do loose their elasticity over time. You should be able to find a decent der. fairly cheap, especially if you look on ebay.
The general rule for chain length is.... Wrap it around the largest cogs without going through the derailleur. Then add two links.
I strongly doubt that chain length is your problem, nor the RD cage springs, which if either were the case, you'd have slack in the lower loop when using smaller sprockets.
I suspect that high gear (outer) limit isn't set in far enough. Often the RD is hanging on the wire, so the limit seems OK, when if fact it isn't. Tighten the limit by degrees until the bike cannot shift to high gear, then back it off slowly until shifting is just possible, then a hair more so shifting is reliable and crisp, but no more.
That should solve the problem. If not, double check that the hanger is square, and the RD cage isn't bent.
Last edited by FBinNY; 11-26-2010 at 01:45 PM.
The key to solving any problem is to understand and address the underlying cause.
im having near enough the same problem with my bike we have indexed the gears and the gear are now working but on the right hand side they are not jumping on to the bigger gog.what can i do to make this work