brake issue

66 273 MANUAL drum brake, single pot MC. It was a running project ( sorta) NO brakes, so I rebuilt ALL the brakes, and as in NEW MC, wheel cylinders, shoes, hardware, hard and soft lines, bled it manually and all was good. Yard drove some, normal pedal and stop, the steering box is complete shot so it sat. It sat and when I did move it around the yard, the pedal got harder and harder, like rock hard now and yes it will stop. The pedal barely moves at all!
I have never had this happen in all my years. Whats up!?????