New Orange Line trains are back in service Monday morning after crews spent nearly four days investigating and inspecting the brakes.
Last week, all new Red and Orange Line trains were pulled off the tracks after one train experienced a problem in one of the train’s 48 braking units. The MBTA said it removed all new cars from service, "out of an abundance of caution," while engineers and technicians worked to determine what caused the problem.
Preliminary findings indicate that one bolt in one of the car’s eight braking units had not been properly installed at the manufacturing plant. MBTA vehicle maintenance personnel started a fleet-wide process to verify that each bolt (24 per car, 144 per train) was properly installed.
Get Boston local news, weather forecasts, lifestyle and entertainment stories to your inbox. Sign up for NBC Boston’s newsletters.
As each bolt on a six-car train passes inspection, the train is being returned to passenger service. To this point in the inspection process, the issue has not been found in any other braking units, the MBTA said.
