My question is do vacuum servo's on front axle assemblies go bad? I've never seen one actually quit working. The t-case engages and the vacuum lines at the servo are reading 15 hg's. When I engage the axle by pushing the servo over manually the 4WD engages and works fine. It will work until I shift the truck back into 2WD and the servo will disengage the axle. Put it back into 4WD and i'm back to crawling under the truck again. Will the part fail again, or should I consider getting a cable set up?