I've never looked at the inside of a MB speedometer, but maybe there is a small, delicate torsion spring that returns the dial (like on other speedos) - if it broke when it was more than halfway around the dial, it would fall all the way forward. Then, it wouldn't move unless the dial saw magnetic impulses going in reverse. I agree with Larry that you have to pull it, but when you do, check for this spring, because if it broke or came loose at one end, you MAY be able to epoxy it back in place and fix it. Good luck!