HELP! I have a 97 expedition. The 4x4 operates by vacuum lines that pulls a bellows lever on front transfer case. Vacuum switching is fine and it pulls around 22hg. Vacuum holds both sides including bellows (no leaks). I tried to manually push the bellows piston but it seams to be seized from the topside leading into the transfer case. Do I need to lift the front tires and rotate a bit in order for the lever to move or is there something else I'm missing?

 

Sorry, Not transfer case it's the differential. Anyway I just saw where someone worked the piston back and forth with wd-40 untill it moved freely. I'll try the same.