I have just had one of my trusty angle grinders give up the ghost on me. Grinding happily away when I thought, above all the normal noise that it makes, that the grinder sounded out of sorts. The next thing I find is the motor is still working but the grinding disc has slowed right down. Upon stopping I find the drive to the disc has failed. Stripping of the grinder reveals that the helical drive on the end of the main shaft has all the teeth flattened. The gearbox teeth are all OK! I will add picture when I can work out how to transfer it from an email my lad sent me into my pictures file.