braking..........

When the brakes are applied, a terrible shaking happens until van stops fully. any suggustions???

Maybe warped rotors.

I had that same shaking when our van had about 220k miles on it. I put up with it for a few thousand miles, was never able to tell if it were a left or a right brake. I didnt even know if it were a front or rear brake - but the rear brakes were drum type, and they dont usually warp to speak of.
I had examined the rotors carefully and both looked fine, no uneven areas or difference in the wear pattern. Finally I got a rusty rotor from a junkyard van (hoping it wasnt warped too) and after mentally flipping a coin to choose, I replaced the right side first. The shaking was gone, braking is nw smooth as silk. I never did see any reason for it. Maybe if I had used a micrometer run-out gauge I would have seen that it was warped.