Ford

I have replace the master cylder but that was not it

I own a repair shop,and it may have a bad master cylinder on it,,or the equalizer may have went out on it,,other people call it the proportioning valve ,but it is what give equal pressure to the front and rear of the vehicle,,you might want to check and see if that is it,,nice luck with it,i hope this help,s.,,have a nice x-mas.