2008 expedition brake problem!

08expedition08

Hello, I have a 2008 Ford Expedition. When I first start it up after having sat awhile the brake pedal will go all the way to the floor. I’ll let off the brake and press down a second time and it functions as intended. I have already replaced the master brake cylinder after a friend mechanic thought that was he problem, however it does the same thing with a new master cylinder.

Mr_Shiftright

Was the new master cylinder bench-bled before installation? You might also try pressure bleeding the system.