If you pulled the center shaft out you would need a locked center diff. I really don't see why you would do either of those things though. Diffs need oil for two reasons. The first being to lubricate them. Running your diffs dry will wear them out very quickly. The other reason for oil is to tune them. You use different weights or thickness of oil to tune the diffs to do different things. I really don't know why you would want 2wd.
