Bad Vibration when braking at high speed

My 2005 Freestar Vibrates terribly when braking from high speed. It is NOT the brake pads or rotor, feels like loose in front end, but no shimmy even at 85+MPH. Could it be a steering part or suspension part?

I can't say about your y/m. On older, different makes and models, I've seen the piston freeze-up in the brake caliper, cause a terrible shudder, when you step on the brake. You might check for ABS codes, see if it shows anything.

These actually had a known issue of brake harshness caused by the rear brakes. Ford made an updated pad and rotors were to be turned if not too rusty.