Ian, The Hammer Action itself is not too bad to deal with and the easiest way I can think of is leave the Selector on the gearbox, this allows you to also use the torque setting if you wish. The other problem is most Hammer drills are 2 speed and once youve taken the drills casing apart you need to fix this selector in place. We re-made the gearbox housings taking out all but the ring/planet gears needed and placing them in an aluminum housing. The 30V gearboxes were made completly in the wheels and on the 12V ones we left all three stages in so this featherweight is really slow but it burnt a few motors out on the higher ratio so this was a safer option.