Sunbeam Alpine Series 2, Brake questions

Have a Sunbeam Apline Series 2 . Have rebuilt all wheel cylinders and turned
drums and put in new shoes. Have put new pads on front disks. Have bleed
system. Problem, I still feel as if I am getting too much brake fade There
isn't the amount of resistance that I would expect from this system. When I
open the filler tank to add brake fluid, when the caps is removed I can hear
air rush in as if there was a vacumn effect. I am thinking that on a sealed
hydraulic system this shouldn't occur and think I might need to rebuild the
master cylinder. Any advice on this scenario?
I am also in need of a photo of the emergency brake setup from beneath the
car if anyone might be able to help me with this. I'm putting a new cable in
as the old one was frozen and want to make sure I have all the right parts
in the right places.
Thank you,
Rudy