brake pedal sticks down

yes it is...while your at it put up a combo booster/master cyl in it and replace both..... unless the master is fresh or been replaced

Master cylinder is internaly leaking. If the booster goes out you lose power assist. It's only doing it started I'm assuming because with the power assist you now have enough force to overcome the seals. If the rear of the master cylinder is leaking into the booster then it is nessesary to replace both

I'm betting on the master cylinder, I think there is air in it for whatever reason. I will report back after replacing it. I doubt it is the booster.

repjlaced master cylinder and the problem remains. I may start looking at the ABS system for answers

Classic problem on F150s. Symptom is brake pedal fade almost to floor when pushed and held, no Red BRAKE light, and no ABS codes thrown. Replacement of Master Cylinder is no help. The problem is going to be a failing ABS Control module. It is the device that causes a buzzing sound/feel at the pedal which will push back at your foot in a skid or error condition..

I replaced the from t brakes put a new master cylinder and a new booster. Blade pedal still doesn’t come all the way up I have pull it back with my foot before I accelerate ????

I have replaced everything except the abs module and still have the problem of pedal staying down.....ABS module replacement on order... hope that works!

Did changing the ABS module work?

I have a 97' F250 doing same thing and replaced Master Cylinder and Booster already to no avail!

Did changing the ABS module work? - same issue here