What was found
DURING THE CLIMB, THE CREW REPORTED THAT THE HYDRAULIC NR 3 PRESSURE DROPPED TO ZERO WITH A GEAR DISAGREE MESSAGE AND A "HYD3A" MESSAGE. THE FLIGHT RETURNED TO ORD, LANDED WITHOUT FURTHER INCIDENT, AND WAS TOWED TO THE GATE. MAINTENANCE PERSONNEL REMOVED AND REPLACED A HYDRAULIC BRAKE LINE. OPERATIONAL AND LEAK CHECKS WERE SATISFACTORY AND THE AIRCRAFT WAS RETURNED TO SERVICE.