It is possible that the needle is not secure on the shaft. Once the speedometer is out and the bezel removed lightly twist and lift the needle to remove it, you may realize right then that it was loose on the shaft. To replace; point it at 30mph and lightly twist counterclockwise and push on to shaft, tap it lightly to secure it. No need to say this is a delicate operation and care must be taken. After bezel is reinstalled test with a reversible/variable speed drill attached to the tranny end of speedo cable. That saves you putting it back into the dash only to find out further repair is needed. Good luck!

Ed