Why is my Mazda MPV jerking when I back up?

Your new brake pads are rubbing against the brake drums. you need to get a professional to turn the drums to make them even. The old brake pads have worn them unevenly and the new thicker pads are rubbing against it causing the jerking. It is jerking when you are going forward too but you don't notice it because you are going faster then when you are backing up.