i'm needing to work on the 4x4 system of a 2003 f-150. when you shift it into 4x4, the little vacuum actuator on the front axle moves, full stroke, like it should, and the transfer case shifts into 4x4, but the front wheels never kick in and pull. my buddy who is a service mgr at ford says the shifting fork in there is probably broken. has anyone had to deal w/ this problem? how much time will it take to fix? how do i go about it, just take the front cover off, and that's it? thanks in advance