I just restored a 70 fastback I did not drive before i restored it. I can,t get the brakes to work rights. When it was restored I replaced the following with new parts. Booster ,master clyinder (twice), lines,combination valve,rotors,drums , wheel cylinders, calipers,pads and shoes. The brake will not lock up it feels like somthing iis stuck under the pedal . works fine when you bleed the brakes . The pedal feels good and I can feel the booster working when I start the car. I am running a cam but have run larger with no problem. Let me know if you have any ideas.
Thanks

 

Did you bench bleed the master cylinder before hooking it up?

 

I just did a major brake job on my car and had to bench bleed it 3 times before it worked right.the problem is the proportioning valve had lots of air in it,the air kept migrating into the master cylinder.the master is tilted up slightly and air cant escape.it has to be tilted down at front to let air escape.Its always a good idea to soak the proportioning valve body in brake fluid overnight before installing it.