40 years as a mechanic.. I have never seen a booster to be intermittent...
except for internal booster damage failure.. never seen the pedal go to the floor..

booster working you have power brakes
booster failure you have Manual brakes.

 

Just my opinion based on the information provided.


If you are positive that the offending caliper is OK, and the lines to the offending caliper are OK, then the only other thing it can be is the MC. A booster won't cause the pedal to sink like you describe, or to pump up.

 

I think you probably solved most if not all of the problem by bleeding them.
If there is any left, it usually will migrate up and caught by the MC.
Try bleeding them a bit more and just drive it a bit and see if it improves any.
RockAuto has the booster from Motorcraft for a tad over $100. DIY and save.

Griz

 

The booster can't be bad. Only thing booster does is help with pushing the piston in the master cylinder. the rod from the peddle goes into the booster where it connects with another pin that goes into the master cylinder. There is a bladder inside the booster that works off engine vacuum. So if the booster is bad than you will have a vacuum leak and the motor will miss when applying the brakes plush you should be able to hear it hiss. Don't buy a new booster.
Like the guy said bad booster manual brakes . Good booster power brakes. Easy as that.

 

Problem solved. Bled brakes again, and brakes still the same. Decided to take the truck to the Ford Dealership where I live. On the way to the dealership I stomped on the brakes very hard just in case there was some dirt or grit causing the problem. Wahlaa! Wow, the brakes are working good now. I went to the ford dealership anyway and had them test the brakes. They said they are working fine, that maybe some dirt or grit got in the ABS unit and that my stomping on the brakes lodged it loose. Anyway they are working like they should for now. The other dealership that tried to sell me a Brake booster are crooks. Nothing wrong with the one on my truck. They just tried to give me a snow job.
Mel