ok heres the deal... i switch it into 4X4 when im going down the road on level ground or even just moving along up hill or whatever i can feel a difference in how the truck handles... but if i lose traction say on ice or snow my rear wheels will spin like crazy but the fronts dont do anything. either of em. my friends say that my 4X4 isnt working then but i dont know as i said i can feel the 4x4 working when i have traction its just when i lose it...
i have an 87 2.8L v6 TBI. it has the shift on the fly stick on the floor.
-Wes-

 

Nothing special about it. Your front axle just is not being engaged. There is a vacuum switch on the transfer case that supplies vacuum to the front axle actuator (on the fender) when in 4wd. The actuator intern pulls on the cable which engages the front axle.