i have a 2002 f150 with 134000 miles, never had trouble with the 4x4, and today i switched into 4x4, the dash says it switched in but the front wheels dont spin and no noises(clunking, grinding )

 

Don't know them well but this works for the Super Dutys, put it in 4x4, make sure light is on, make sure it's in park and the rear wheels are blocked. Jack up one front wheel and turn it. Watch the axle, if it turns with the wheel it is locked, if not the problem is in that hub, if that axle turns, look at the front driveshaft, if it turns than the front end is locked but the transfer case isn't. If the driveshaft doesn't turn than look at the opposite axle, if it turns the opposite direction then that hub is not locked. It's a start .

 

two things happen when you put it into 4 x 4. If your in 4 HI, all that happens is vacuum is applied to a small cylinder on the front axle and put pulls or pushes a pin into the engagement. there are two hoses, check vacuum on each. They come from two solenoids on the firewall.... The second thing that happens, is if you put it in 4 LO. then a motor on the side of the transfer case moves the gears into LO range and you get a second light on the dash.