So I have all original brakes. A new master cylinder new brake lines and rubber flex lines. Took apart the brakes cleaned and set brakes . Then honed the cylinders. Did not replace the brake cylinders or rubber cushions as they seem to work fine now. Bled the brakes and pumped up the brake pedal. At this point the brakes work good. A few days later the pedal goes to the floor . I can pump up the pedal and again have brakes . Every few days of non use the same thing and I must pump up the brakes then it is good for a few days. What is going on. Where is my brake pressure going? Any help would be great. 1950 216 gmc 1/2 . Thanks
