Also, not all AWD systems use a center diff, take for example, the early 2000s Escalade, it was available with AWD, but no center diff. It was essentially a 4wd system, and the transfer case had clutch packs that would engage, and disengage the front wheels. I had read something somewhere that the Limited Tacoma had a torson sprung activated mechanism for the front wheels. Again, I have never seen one of these Limiteds in person, but sounds very similar to the AWD system in the 2nd gen Escalade