New master cylinder and flexible brake lines. I had brake problems which were from leaky front wheel cylinders. New POL front disc conversion which went swimmingly.. Until I pressed brake pedal. They are closed now and I'd like to sleep with some answers. I've bled brake lines many numerous time by vacuum and by assistant. I'll guarantee there's no bubbles. But there's no brakes either...spongy pedal just won't pump up except a tiny bit after 10 pumps. Pedal returns on it's own. Supposedly the front disc conversion is solid on the 50 Merc using original master cylinder but some say residual valves needed, some say bigger master is a requirement. Anyone else go through this situation and know the answer???