I have a 1998 F150, 4x4 Lariat 136,000 miles. The 4 wheel drive, front wheels won't engage. It has the switch on the dash, not manual hubs. The shaft off the transimission engages went I flip between 2 and 4.
The vaccum lines go to a round black unit, middle front of the front axle. Does this push/pull the axles to hubs, or what does it do? I haven't found any lines/wires to the hubs other than the anti-lock brakes. It also has a vent hose that goes up in the motor compartment.
I guess this is an education session. Where should I start?