As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: WHILE TAXIING OUT FOR DEPARTURE, AIRCRAFT BRAKES GRABBED ABRUPTLY ON THEIR OWN AND AIRCRAFT PULLED HARD LEFT. SUBSEQUENT CHECK OF THE BRAKES, EVEN WHEN SLIGHTLY APPLIED, RESULTED IN ABRUPT BRAKING AS IF FULL BRAKING WAS APPLIED BUT IT WAS NOT. THE AIRCRAFT WAS TOWED BACK TO THE GATE. MAINTENANCE FOUND THE #1 BRAKE FAILED IN THE SET POISITION AND REPLACED IT PER AMM 32-42-27. A SATISFACTORY LEAK/OPERATIONAL CHECK WAS ACCOMPLISHED.