What was found
PILOT REPORTED AFTER BLOCK OUT FOR FLIGHT 8691 - RIGHT BRAKE ON AIRCRAFT FELT SPONGY AND BRAKE PEDAL, WHEN FULLY APPLIED, WENT TO THE FLOOR - FAILED. THE ACFT WAS RETURNED TO THE PARKING RAMP FOR MX TROUBLESHOOTING. R & R RT BRAKE ASSEMBLY IAW MM 32-40-00. R & R RT BRAKE MASTER CYLINDER IAW MM 32-41-00. R & R PARKING BRAKE VALVE IAW MM 32-42-00. BLEED BRAKES EXTENSIVELY IAW MM 32-40-00. ORIGINAL NEW BRAKE MASTER CYLINDER THAT WAS INSTALLED WAS SUSPECTED TO BE THE DEFECTIVE COMPONENT - (BYPASSING INTERNALLY). NEW BRAKE MASTER CYLINDER WAS REBUILT - REINSTALLED AND ALL OPERATIONAL AND FUNCTIONAL CHECKS IAW MM WERE COMPLETED WITH NO FURTHER DEFECTS NOTED. BRAKE MASTER CYLINDER ON-CONDITION PART.