Why is my truck Shacking?

When I apply the brakes to my 96 Ford Bronco (please no cracks on ford, everyone has thier own opinions) 4x4, it starts to shake really bad. I heard it could be my rotters or the bushings. I need a straight answer before I go tearing it apart. Plus, I'm rebuilding it slowly, cause a bronco is what I have always wanted. I just want to know what is cause it to shake when I apply the brakes. Not sure if its comming from the front end or the back end or both, but what I do know is it shakes really bad sometimes. Almost like it is going to shake right off the road. Help... I feel like an idiot, because it is probably something simple, but i like the older model vehicles and they are more durable, once you get them running right.