Brake pedal spongy and slowly goes to floor

Thank you ZeeTech. I've bench bleed and replaced the MS. I still see the slight boiling of brake fluid in the reservoir. I've run a QT of brake fluid thru the system and the brakes are still very spongy?

Check the reservoir's cap, make sure it breathes ( the little vent hole isn't clogged). Some Fords are hard to bleed. Did you bleed only at the MC or at the wheels also? When you replaced the rear shoes, did you lift up the rubber dust cap from the wheel cylinder and checked for leak? Absolutely no brake fluid leak from the system? Zee

Hello Zee, I've bleed all the wheels twice and replaced both the rear wheel cylinders. No loss of fluid I can detect. I suspect your right about difficulty bleeding the system. I'm taking the truck to a pro in the morning to bleed the system using the vacuum method. I'll report the results.

I have a simalar problem. I have replaced the rear calipers in my 2005 f450 motor home and cannot get the brake pedal from goining ot the floor. Worst when it is running. It slowly goes to the floor and slowly comes back up. I have bled all four tires (about 2 qts of fluid). Can't believe there is still air in the system. I did run the fluid pretty low on one occasion and could of sucked more air in. Should I be looking somewhere else or just keep bleeding?