Bench testing a master cylinder

Once the master cylinder has been serviced/repaired it needs to be tested. We clamped the master cylinder in the bench vice and connected brake lines that have been blocked off. To check if the cylinder was working and if it was holding pressure we filled the reservoir with brake fluid and bled the cylinder to get all the air out. We bled it by pushing the piston in with the brake connectors loosened then closed them and released the piston. We repeated it until all the air was out of the system. Then we pushed the piston in with the cylinder completely blocked off to see if it will hold pressure. If the piston keeps going in it means that the fluid is leaking past the piston seals which means that the cylinder needs to be dismantled to find the problem. If the piston stays fixed it means that the cylinder is fine, the cylinder should be cleaned with brake cleaner if it is not going to be installed in a vehicle immediately.