DRIVING DOWN THE HIGHWAY, WHILE COMING UP TO TRAFFIC AND COMING TO A STOP, THE BRAKE PEDAL BECAME ROCK HARD AND MADE IT DIFFICULT TO SLOW DOWN OR STOP IN TIME. IN AN ATTEMPT TO STOP THE VEHICLE FROM CRASHING INTO THE REAR OF THE OTHER OTHER VEHICLES, I SWERVED TO THE RIGHT TO AVOID THEM AND SIDE SWIPED A GUARDRAIL. MY VEHICLE NOW HAS BODY DAMAGED ON THE PASSENGER SIDE. IT HAS BEEN DROPPED OFF AT CONCORD CHEVROLET IN CONCORD, CALIFORNIA. I ALSO FILED A CLAIM WITH MY INSURANCE AS WELL AS GENERAL MOTORS.