Quote Originally Posted by redrhodie View Post
I was about to climb a hill, but was still on the flat when it happened. As I shifted from big to little chain ring (compact double), my rear wheel suddenly locked. I was in the middle of my cassette. I got off, and I could pedal backward, but not forward at all. The chain was not off, and I couldn't figure out where it was jammed. I released the rear wheel quick release, and it unjammed.

Any ideas what that could have been?
I'm not particularly mechanical, but I had sort of the same problem and the bike store technician loosened my cable some. It had nearly thrown me off my bike when it happened.