Axw Man, Thanks for all your very good information, but my problem is the opposite to all above. I do not need the 4WD more than a couple of times a year, so have not missed it until recently noticing a broken vacume line above RH wheel. Traced it and figured it was for 4WD. Got some new hose and replaced it. Now the thing wants to lock in front wheels when in 2H, with some crunching type noise. Stopped that and experimented with it by rocking car back and forth by hand. With engine off, shafts were stationary. Start motor (gearbox in neutral) and rock, both shafts rotate forward and back as they should in 4WD. Pull new hose off and both shafts stationery. Plug engine end of hose to RH wheel and LH shaft rotates forward and back so LH hub locked in while RH shaft counter rotates so front diff works. With motor running and transfer case in H2, connect hose and can hear hub lock in. I guess the question is - is there a problem with the solenoid, or does the vacume need to be connected in a special way to fix it. Since then, I have been just running RWD with hose off. Any help will be Great. PS, do not really want to change to manual hubs.