Sorry I didn't read this thread sooner, that is exactly what I would have suggested checking, as I just had the same issue a couple months ago. And btw, it's called a double Cardon joint, and the axle joints are single Cardon joints. As far as the engaging and disengaging of the 4wd goes, it could be a number of things, but, the first to check is the vacuum. As in making sure you don't have a leak some where.