Is this a common problem w/ Ford 1/2 tons. My right/pass side messed up @ about 40k. I went ahead and replaced both sides. Now the right side is buzzing again in 2wd. While driving the buzzing immediately quits when I hit the 4wd switch. If I remember correctly, the truck is supposed to have the hubs locked when the truck is off. I raised the right front and went thru the following procedure: truck running, selector in 2wd, wheel spins freely, turn truck off and a few seconds, I hear the vacuum "pop" off, but wheel still spins. Restart truck, selector to 4wd, wheels won't spin, turn truck off, wheel still won't spin.
I checked the vacuum: 28. Vacuum on when selector to 2wd position. Are ther any aftermarket options? Truck just has 95k and I try to use the 4wd a couple of times per week: easy 4wd, just driving ona dirt road about 1 mile. Went hunting in Ohio and needed 4wd. When I engaged, the truck thumped several times before engaging. I just hope I don't foul up the splines on the axle