I have read the post on here about 4x4's not engaging. I have just bought a 2001 Ford F150, maual 4x4 engagement. I have the truck on my lift so that I can start the truck and let the wheels turn freely. when I put the truck in 4h and put truck in gear the drive shaft turns but makes a light grinding noise, and the front wheels won't lock in. I checked the actuater on the dif and it seems to be engaging(moving back and forth). I attempted to drive the truck and put it in on th efly and it still does not engage. What could this grinding noise be, or what else should I check. any help would be greatly appriciated.

 

Sounds like the actuator arm inside the diff is broken.

I have never seen one, but I am told it is similar to a transmission shifting fork.