"No feedback brakes" go from nothing to full lock

dICKj said
OK, I will first make sure the push rod is making contact when I move the pedal. Then I will make sure that there isn't a vacuum leak anywhere else. If no luck, then I will remove the booster and go manual brakes. What size piston bore do I need in the master cylinder for manual brakes. Anybody got a part number for Dorman, O'Reilly, or Auto Zone?

What size master cylinder do you have now? How are we supposed to recommend a master cylinder without knowing what you already have? Especially if there could be an issue with what you have now?

And, back to my original question, are all 4 wheels locking up at the same time? Because if they are that narrows things down significantly.