Internal leakage in the master cylinder should have made the red "Brake" warning light turn on. Did that happen? An external leak will do that too.
Was this a used or rebuilt master cylinder? If it was used, you must never push the brake pedal more than halfway to the floor. Doing so can damage it. It is okay to do that with a rebuilt one or when it's up to about a year old. Crud and corrosion build up in the bottoms of the two bores where the pistons don't normally travel. Running them over that crud, as in pedal-bleeding or when surprised by a sudden, unexpected leak, can rip the lip seals.
If the master cylinder is okay, there may just be too much air in the system to get the brake fluid moving. I only use gravity-bleeding but you have to leave the cap loose on the reservoir, otherwise vacuum will build up in there and prevent the fluid from running down. It can take a good 15 minutes for fluid to show up at a wheel. If the master cylinder was allowed to run empty, you may need to irritate the brake pedal a little to get the fluid flow started.
If your car has anti-lock brakes, many hydraulic controllers need to have some valves opened with a scanner to get the air out. That should not be an issue if the reservoir never ran empty.
Did you bench bleed the replacement master cylinder? The next time you need to replace one, there is an easy trick to avoid having to bleed at the wheels, although that gets a little involved on Fords when they have four steel lines coming out of it. When there's only two steel lines like on most other brands, replacing a master cylinder becomes a half-hour job with almost no bleeding necessary.
Wednesday, March 18th, 2015 AT 7:01 PM