Master Cylinder: Notes
WARNING: This page does not describe the selected car, but rather 14 other vehicles, including the 2004 Ford RV Cutaway, 2004 Ford Econoline, 2004 Ford E450 Super Duty, 2004 Ford Cutaway, and 2003 Ford RV Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
To check master cylinder for internal leak, disconnect brake lines at master cylinder. Plug outlet ports of master cylinder. Apply brakes. If pedal height cannot be maintained, master cylinder has internal leak and must be rebuilt or replaced.