Steve, If your drill is indeed switchable and not just a impact driver, if the hammer mode switch feels sloppy or to easy to switch, the switch has came out of position or broken a tab inside drill. If switch seems normal but you are not getting hammer mode the wing disc and gear could be seized, worn or broke. I will post a link, not your model but should be similar to show how the hammer function works and the common components. Good luck.

I hope this helped you out, if so let me know by pressing the helpful button.

http://www.finehomebuilding.com/2010/02/...