When you stomp the brake pedal all the way to floor it engages the back brakes as well. You should hear a creaking noise from the drum brakes with the brake pedal all the way to the floor. Similar sound to having the handbrake on and it creaking when it takes the full weight of the car. I didn't know this either.
i went back to the local repair shop and they had told me all they did was replace the brake pads and discs and that was that.
I i could've sworn he said he adjusted something but i dont know. I just know that scratching, creaking sounds are all gone. So either i got a bad set of brake pads or the disc was warped in some way. But the brake pads from Ford which had motorcraft on the backside are totally dinged sanded and look as if someone took a hammer to it. I dont want to say this will fix your issue but i'd take it to a local repair shop that you can trust. I used one from the good garage scheme if you get nowhere from your local dealer.