-Make sure the gear box is set in low and the clutch is fully engaged to the maximum.
-Start off by removing the screw down inside the chuck (It is left handed threads).
-Once you have removed the screw, put the small end of a large allen wrench inside the jaws.
-Take a hammer and hit the long end of the allen wrench counter clockwise, which is normal thread, until it comes off.
If it doesn't come off then you can spray some WD-40 down inside the chuck and try these steps again in an hour or so.
Good luck!
Don- www.toolsandmachinery.com, March 2009