WHEN COMING UPON A STOPPED VEHICLE ( APPROX 10 CARL LENGTH AHEAD OF MY CAR ) I WAS TRAVELING AT ABOUT 25 TO 30 MPH WHEN I APPLIED MY BRAKES TO GRADUALLY SLOW DOWN BUT ALL I GOT WAS A VIBRATION FROM THE BRAKE PEDAL BUT NO BRAKING. I CONTINUED A FIRM PUSH ON THE BRAKES BUT ROLLED INTO THE STOPPED VEHICLE WITHOUT ANY SLOWING OF MY VEHICLE. I HELD THE PEDAL DOWN SOLID WITH NO PUMPING. THE TRUCK IN FRONT OF ME SUSTAINED LITTLE IF ANY NOTICEABLE DAMAGE. I HAD TO BE TOWED.