I WAS DRIVING 75 MPH ON THE INTERSTATE WHICH WAS THE SPEED LIMIT AND I VIVIDLY REMEMBER HAVING MY CRUISE CONTROL SET AT THAT SPEED, PLUS OR MINUS 2 MPH. I WAS DRIVING BEHIND A PICKUP TRUCK THAT WAS 8-10 SECONDS AHEAD OF ME. THE PICKUP TRUCK WASN'T EQUIPPED WITH CRUISE CONTROL LIKE MY BLACK 328I BMW WAS SO THEY (A COUPLE) WERE TRAVELING SLOWER THAN I WAS AT THAT TIME. SO AS MY VEHICLE APPROACHES 4 SECONDS AWAY FROM THEIRS TRAVELING 75MPH (+ OR - 2 MPH). THEY BRAKED TO CHANGE LANES FROM THE LANE WE WERE TRAVELING TOGETHER TO THE OTHER LINE SINCE IT WAS A TWO LANE HIGHWAY. THEY DIDN'T SLAM THEIR BRAKES, THEY LIGHTLY PRESSED THEM BECAUSE A THIRD VEHICLE THEY WERE WAITING TO PASS IN ORDER TO SAFELY SWITCH LANES AND GIVE ME THE RIGHT AWAY. QUICKLY, I REACTED BY BRAKING AS WELL AND I COULD FEEL A HYDRAULIC LOCK IN THE BRAKE PEDAL. ALMOST LIKE I WAS TRYING TO PUSH DOWN ON CEMENT AND MY PEDAL WASN'T ACTING NORMAL WHILE BREAKING BUT ONLY HALF BREAKING LIKE IT WAS FULLY APPLIED WHEN I WAS PRESSING FIRMLY. I'M CONVINCED THAT THE VACUUM PUMP THAT SUPPLIES BRAKE POWER ASSISTANCE MAY HAVE BEEN MECHANICALLY FAULTY AND/OR FAILING FOR REASONS ONLY A MECHANIC COULD UNDERSTAND. NOW, I'VE BEEN A DRIVER FOR MANY YEARS AND THIS WAS MY FIRST BMW SO I DIDN'T KNOW WHAT TO THINK OF IT. I BOUGHT IT FOR A GREAT DEAL AT A PRE-OWNED CHEVY DEALERSHIP THAT SAID IT WAS ASE CERTIFIED BY THEIR MECHANICS PRIOR TO SELLING IT TO ME. SO WHY DID THIS HAPPEN TO ME? I'M ONLY 27 YEARS OLD, WITH THREE CHILDREN AND I COU