I have a 2000 Ford F-150 super cab with 5.4L. I looked through the diagnosing thread and didnt see an answer to my problem. When i put my truck in 4wd (switch on the dash) the transfer case engages and checked to make sure drive shaft was moving when was engaged. I then jacked the front up and had my wife turn on the 4wd to check the vaccum actuator at the front differential, looks to be working as the actuator compresses towards the passenger side. Still the front does not engage. I havent pulled anything apart on the differential yet, any thoughts on what i could be looking at to fix this?

 

Look at what the actuator is doing.
Is it moving the lever in the differenial?
If yes the fork assembly is in trouble.
It moves a spline collar to engage the output with the differencial.
Good luck.

 

Yes it moves the lever on the differential. How difficult is it to replace or fix the shift fork?