As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: FLIGHT CREW REPORTED THAT THE BRAKES VERY SLOW TO RESPOND EVEN WITH MODERATE PEDAL PRESSURE. WHEN INCREASING PRESSURE BEYOND NORMAL PEDAL INPUT BRAKES WILL SURGE. MAINTENANCE REPLACED BCSU PER AMM 32-42-34 AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK.