Hey corky,
you can just keep trying and it should come off eventually..:) it looks like there is a spot to put a thin wrench on the spindle shaft[behind the chuck] to secure it[and then smack it!]
hope this helps...
Craig

HEy Corky,
I may be wrong,but have you taken the left ahnd threaded screw out from the inside of the chuck?if you have/or have not you have to get that out,sometimes its a real toughy to get out .then you'll have to drill it out.

other than that the only other way I kno of is by cutting it off by using a metal chopsaw,first of all you need to insert a screw driver into the chuck when the jaws are open until it touches the back of the inside,then make a mark on the screw driver where it is just outside of the chuck,then you use that measurement on the outside,and you now make a mark on the outside of the chuck,and thats where you'll cut with the chopsaw,after that the chuck should be easier the knock off wit a old cold chisel or punch.
if it won't come off still.you may wanna lock the machine in a table vice(be careful not to over thighten,or you cud crak the machine's casing) then take a small angle grinder,and you slowly gring the top part of the chuck away,then you do the same thing to the oposite part of that ,and the two halves shud be able to come off.

Good luck

Quincy
Guyana
South America

I found there was no internal screw, I did not have a thin wrench the right size so I used a needle nosed vice-grips and use a pipe wrench to turn the end of the chuck, I installed a Jacobs chuck made in China which failed almost immediately under hammer drill stress. I just ordered what is supposed to be a Makita replacement. If that doesn't hold up I saw a different brand hammer drill that has a German chuck. I think the internal parts made need to be forged rather than cast to hold up to hammer drill stress and I am willing to consider any option if the new Makita chuck bites the dust.