1990 Chevrolet Suburban

I WAS ENTERING THE I-205 SOUTHBOUND ON RAMP OFF OF MILL PLAIN BLVD IN VANCOUVER, WA WHEN THE DRIVER OF THE CAR IN FRONT OF ME SUDDENLY APPLIED HER BRAKES. I ATTEMPTED TO APPLY MY BRAKES, BUT THE BRAKE PEDDLE WENT LIMP ALL THE WAY TO THE FLOOR. I TRIED TO PUMP THE BRAKES, BUT THE PEDDLE STAYED LIMP AND ALL THE WAY TO THE FLOOR. I DIDN'T PANIC BECAUSE I DIDN'T SEE ANY REASON FOR THE DRIVER TO SLAM ON HER BRAKES--THERE WAS NO ONE IN FRONT OF HER AND THERE WAS NO ONE PULLING IN FRONT OF HER, AND WE WERE ENTERING THE I-205 ON-RAMP. THERE WAS PLENTY OF ROOM BETWEEN OUR VEHICLES. I FIGURED THAT THE DRIVER OF THE OTHER VEHICLE WOULD MOVE ON AS WE WERE ON THE FREEWAY ON-RAMP. SHE THEN CAME TO A COMPLETE STOP ON THE FREEWAY ON RAMP. AT THIS POINT THE SPEED WAS PROBABLY LESS THAN 20 MPH. AS I WAS REACHING FOR THE EMERGENCY BRAKE, MY SUBURBAN BUMPED INTO THE BACK OF HER 1987 ACURA. AFTER THE ACCIDENT, THE BRAKES ON MY SUBURBAN WORKED FINE. I TOOK MY FOOT OFF OF THE BRAKE PEDDLE AFTER BOTH VEHICLES CAME TO A COMPLETE STOP FROM THE IMPACT MOTION. I THEN PUSHED ON THE BRAKE PEDDLE AND IT WAS GOOD. I BACKED UP A BIT AND THE BRAKES WORKED FINE. I DROVE FORWARD A BIT AND UNTO THE SHOULDER AND THE BRAKES WORKED FINE. THE ROAD WAS DRY AND THE SKY WAS SUNNY. I COULDN'T EVEN FATHOM THE BRAKES FAILING FOR A COUPLE OF DAYS, THEN IT DAWNED ON ME THAT SINCE THEY FAIULED ONCE THEY COULD FAIL AGAIN ABD POSSIBLY WITH MORE TRAGIC CONSEQUENCES. I TOOK THE SUBURBAN TO VANCOUVER CHEVROLET FOR A BRAKE CHECK AND EXPLAINED TO THE WHAT HAD HAPPENED. THEY SAID THAT THE MASTER CYLINDER WAS LEAKING DOWN AND REPLACED THE MASTER CYLINDER. I DON'T FULLY UNDERSTAND WHAT MASTER CYLINDER LEAKING DOWN MEANS. I CHECKED THE BRAKE FLUID LEVEL AFTER I GOT HOME AFTER THE ACCIDENT AND IT WAS GOOD. I HAD NEVER HAD ANY PROBLEM WITH A LIMP BRAKE PEDDLE ON THE SUBURBAN BEFORE. I NEVER HAD ANY PROBLEM WITH THE BRAKE PEDDLE. THERE NEVER WAS ANY SPONGINESS OR ANY ANY INDICATION OF A BRAKE PEDDLE PROBLEM PRIOR TO THIS INCIDE