A PA11 PILOT REPORTS RUNNING OVER A TXWY SIGN AFTER EXITING THE RWY AT HIGH SPD; APPLYING BRAKES TO SLOW; BUT ONLY ONE BRAKE WAS FULLY FUNCTIONAL.

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ACFT INVOLVED WAS ON 11 X 25 X 4 'BIG TIRES' AND DEPARTED FROM ZZZ EARLIER IN THE DAY FOR PLEASURE FLT WITH ONLY THE PLT ON BOARD. SEVERAL OFF-PAVEMENT LNDGS WERE MADE BEFORE RETURNING TO ZZZ. LNDGS WERE MADE ON SAND GRAVEL BEACH; GRASS STRIP; AND RIVER BARS WITH NOTHING RAISING CONCERN. LAST LNDG PRIOR TO ZZZ WAS TO PICK UP A PAX AT A GRASS STRIP AND FLY 10 MINS TO LOCATION. PLT HAD CURRENT ATIS AND WAS CLRED TO LAND ZZZ; MADE A GOOD LNDG ON RWY 19R WITH WINDS 270 DEGS AT 8 KTS. ACFT MADE L TURN FROM RWY 19R ONTO TXWY C APPROX 15 MPH GND SPD; AND THE PLANE CONTINUED IN A LOW ARC L TURN. PLT APPLIED BRAKES AND ONLY L BRAKE HAD PRESSURE. PLT IMMEDIATELY APPLIED FULL R RUDDER AND DOWN R AILERON WITH NO NOTICEABLE RESULT. PLT ADDED PWR WHILE HOLDING R RUDDER AND AILERON AND ACFT RESPONDED WITH CORRECTION TO THE R; HOWEVER; THE L GEAR COLLIDED WITH THE TAXI SIGN 'C;' DAMAGING THE SIGN BEYOND REPAIR. MINIMAL APPARENT DAMAGE TO ACFT ON IMMEDIATE CURSORY CHK BY PLT AFTER PARKING. ACFT WILL BE CHKED BY A&P/AI. PLT HAD RADIO COM WITH THE FLT TWR (CTLR SAW THE COLLISION)AND TAXIED TO PARKING WITHOUT STOPPING OR FURTHER DELAY. CONTRIBUTING FACTORS: WIND; ACFT TAXI SPD; POOR R BRAKE CONDITION. HUMAN CONSIDERATIONS: TAXI FASTER THAN NORMAL DEPARTING ACTIVE RWY; FAILURE TO CHK GEAR AFTER OFF-PAVEMENT LNDGS TO SEE IF ANYTHING WAS OUT OF PLACE OR DAMAGED. PLT SHOULD HAVE GIVEN MORE CONSIDERATION TO WIND DIRECTION KNOWING HE WAS TURNING TO A QUARTERING TAILWIND.