Help !!! I have Never had my 4x4 quit working

 

The most likely reason for a sudden loss of 4 wheel drive engagement is the vacuum motor on the passenger side of the front axle. Most likely one of the two small vacuum lines going into it got pulled off. They run from the driver side of the transfer case into the wire loom, and then to the axle. One line is for engagement, the other for disengagement, so if the engagement line gets pulled (or if there is a break in the vacuum line) it won't engage. The next most probable scenerio is that the vacuum motor itself is bad. It uses a diaphram to pull a sleeve that connects two short axles in the housing. If the diaphram is bad, it won't shift the sleeve. You can get a new one at any parts store or most junk yards. 4x4 Posi-Lok is a cable replacement that is alot more reliable for around $200, though it requires a hole to be drilled in the floorpan.