Hi Frustrated - your mechanic's not wrong but he's probably being a bit of an arse by not explaining properly!! Yes you do need the IRD to drive the front wheels, but if you only want 2wd you can blank off the output pinion on the IRD where the propshaft to the rear wheels normally bolts - you can even buy IRDs specifically for 2wd with it already blanked. However it isn't really necessary to blank it off for short periods sans propshaft if you plan to put it back on. And if you don't, be sure to notify your insurance company as converting a 4wd to 2wd is a substantial modification and will quite likely invalidate the insurance if you fail to declare it!!