Ford

We own a 1999 ford windstar that is a perfect ride, except for when we are on the highway. when we go over the speed limit and then slow back down, the van shimmers as we are braking, but only between certain speeds. for instance, as we are slowing down, it starts to shimmer at 85 kpm and disappears at 60 kpm. anyone have any ideas what is going on?

If it happens while you are braking i would say you have a warped brake rotor