Join Date: Apr 2003
Location: St Louis, Missouri
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Stand your bike up vertically against something and look at your derailleur from the back. Your derailleur arm should be vertical. Your description of your shifting problem, especially after a crash, is often the result of a bent derailleur hanger.
Assuming I'm right, you have a few options.
1. You can try to bend it back by hand and eyeball it into vertical. This often works and it's cheap, but it's imprecise at best and at worst, it can totally ruin your frame.
2. You can have a shop bend it back. They should have a tool that gauges the allignment so it should be more accurate.
3. Many aluminum frames have a replaceable bolt on derailleur hanger. If yours does, buy two. Finding the exact replacement that you need when you want it can be a frustrating process.