Did the tire ever get inspected for bumps or malformations on its surface? A bump or un-even wear on a tires surface can cause severe vibration and bouncing especially at higher speeds and unser braking. I thought of this first becasue it was only happenning at one corner of the car. Definately check that tire as that is a very dangerous problem.
Are either of the rotors grooved or ridged at the edge. If they are grooved that will cause vibration under braking and if the edge is ridged they are probably too thin and need replacement.
The pedal going to the floor is either air in the lines or the master cylinder or brake booster is failing.
A quick test for the brake booster;
Before starting the car, pump the brake pedal until it is firm.
Then keep pressure on the pedal and start the car. If the pedal falls towards the floor from just the weight of your foot, the booster is more than likely not the source of the problem.
Check for fluid leaks under the dash where the push rod goes from the brake pedal into the firewall.
Wednesday, November 9th, 2011 AT 2:38 PM