A power driver may include a housing, a tool chuck and a power take off mechanism. The tool chuck may have an input shaft mounted for rotation on the housing. The input shaft may support threaded chuck jaws. A chuck actuating shaft may be mounted for rotation on the input shaft. The chuck actuating shaft may be screw coupled to the threaded chuck jaws. The power take off mechanism may be connected to the tool chuck. The power take off mechanism may be adjustable into a DRILL DRIVE MODE to rotationally drive the input shaft and the chuck actuating shaft together as a unit, and a CHUCK MODE to rotationally drive the chuck actuating shaft relative to the input shaft. The power take off mechanism may be internal of the housing. The power take off mechanism in the CHUCK MODE may rotationally fix the input shaft to the housing.