Got a question about the 4WD on my '05  F-350.  I know I've got a vacuum leak on my 4WD system so I've been using the manual engagement on the front wheels till I have time to find and get it fixed.  The question I have is when I've engaged the front wheels using the dash switch I get a lot of torque binding on the front wheels when I take a sharp turn while at the ranch.  I usually am switching in and out of 4WD a lot depending on where I am while out there.  The thing I wonder about is this doesn't happen, the binding, when the front hubs are engaged manually and I take the same sharp turns.  Does this mean that even though the hubs' manual switch is turned to the "engaged" position something's broken and I'm really not getting power to the front wheels?

Thanks for any answers or suggestions!