I changed all the braking components on my 74 E type. Master cylinder, brake servo and servo cylinder. One way valve all vacuum hoses and all brake hoses. The problem I am having is that the brakes bleed fine. I drive the car and after a while I notice the pedal starts to slowly move downwards. When I check the system I notice that the Master brake reservoir emptys and fills the servo reservoir causing it to overflow. Any thoughts?

 

I think it's a check valve. (can't remember which one) Look into that. Too late for me tonight, or I would do it for you.