Mine was very sudden. Drove to work and it was a very rainy day, but it drove fine otherwise. When I left for work, it was starting to grind and I had to take side roads to get home. Once home, I let the cool for an hour and decided to take it for a spin to see what's up and it wouldn't really move. I changed out the rear hub myself, just had a shop remove/press a new bearing in.We were changing rear hubs and toe links on 02+ Explorer/Aviator models on every single truck that came in. Probably one of the worst rear suspension, brake and toe adjustment designs ive ever had the pleasure of dealing with. Almost every single one needed parking brake shoes, toe links or a wheel bearing. And if you had to replace one, getting the parts off the other two items meant that those needed to be replaced also.
The worst part of it all? The owners who almost always scoffed at the price and would leave the dealership in an entirely unsafe vehicle, sometimes with children in the back.
The front hubs were 3 bolts and swap them in. All in one units are stupid easy to replace. Might take you 45 min per side and that was if the thing was rusted to hell.
My wife had a 2005 Exploder which had one original rear hub and the other side i replaced at least twice in its 225k mile adventure.