Really Pauly? I would've expected something less retarded sounding from you. Unless you meant to say that his rear differential is NOT limited slip. Limited slip, sometimes referred to as positraction (which is a GM trademark for their limited slip differential option) will deliver power to both rear wheels, and let them slip enough to make turning possible without damaging anything. Anyway, if the fronts aren't working, there's probably a transfer case, of front axle engagement problem. I haven't worked on any Toyota four wheel drives for quite a while, so I'd have to look into it more. Is there a lockout hub on each front wheel, or are they automatic (or maybe constantly engaged?) Does the 4wd light flash or anything, when trying to put it in 4wd?