What was found
ON TAXI OUT CA RIGHT BRAKE PEDAL CHATTERED AND THEN WENT TO THE FLOOR. AFTER RETURNING TO GATE NOISE FROM PREVIOUS FLIGHT RETURNED. C/A: T/S IAW A319 TSM 32-42-00-810-841-A & TSM 32-42-00-810-912-A. FOUND #4 BRAKE PISTON AT 1 O'CLOCK POSITION INTERMITTENTLY GRABBING WITH BRAKES OFF AFTER CYCLING. R & R #4 MLG BRAKE ASSY IAW A319 AMM 32-42. OPS & LEAK CHECK GOOD. PERFORMED A/C BRAKE BLEEDING PROCEDURE IAW A319 AMM 32-42 WIP. PER MCC REQUEST PERFORMED A/C MAINT TAXI CHECK AS REQUIRED. NO DEFECTS NOTED. A/C OKAY FOR SVC. (LP: 9586502, AIRCRAFT WAS GROUNDED)