BRAKE FAILURE. WHILE BACKING DOWN MY DRIVEWAY AT A SPEED OF ONLY 10-15 MPH THE VEHICLES BRAKE PEDAL BECAME ROCK HARD AND WOULD NOT DEPRESS, I AM A 220 LB. MAN WHO IS WHAT I FEEL IN GOOD SHAPE AND HAD TO USE BOTH FEET ON THE BRAKE PEDAL AND ALL MY STRENGTH JUST TO ATTEMPT TO SLOW IT DOWN. I WAS UNABLE TO FULLY BE ABLE TO STOP THE VEHICLE WHEN I IMPACTED THE CORNER OF MY GARAGE WHICH RESULTED IN MINOR BUMPER DAMAGE , HOWEVER NO ONE WAS HURT THANK GOD. THE ODD THING IS ONCE I STOPPED AND PUT THE VEHICLE IN PARK THE BRAKE PEDAL SEEMED TO BUILD PRESSURE AGAIN AND WAS FINE? AFTER A LITTLE INVESTIGATION WITH THE VEHICLE I CAN RECREATE THE ISSUE IF I PUMP THE BRAKES 4 TO 5 TIMES IN QUICK SUCCESION WHICH RESULTS AGAIN IN A ROCK HARD PEDAL AND LOSS OF BRAKING. ONCE I REV THE ENGINE IN NEUTRAL I RESTORE PRESSURE BACK TO THE BRAKE PEDAL AND HAVE NO ISSUES. I AM ALMOST POSITIVE THIS IS A BRAKE VACUUM ISSUE AND WILL BE TAKING TO A MECHANIC ASAP TO LOOK INTO IT.