A new experience for me. I heard it snap. I wondered if something had broken. I was in the lowest gear, waiting at the lights. Off I went, tried to change gear, no change gear. I looked and saw that the hook at the end of the spring had snapped off. I can see the shiny metal where it snapped. I pulled the derailleur into third gear and got going again. It changed back into first. Eventually I got fed up with this. I jammed a piece of tree in it which locked it in 4th, thus I got home. Must I buy a new derailleur? I thought my bike must have run out of ideas for ways to impose misery on me, but I was wrong. The bastard is more creative than I gave it credit for. An XX1 derailleur. Buy expensive bits. It is more funny when they break.