I have a 79 F-150 d44 front w/discs 9" rear w/ drums. Everything on the brakes is new except for the drums, one of the brake caliper, and the lines. I cant figure out why but I have virtually NO braking. I can push the pedal all the way to the floor with very little resistance. They don't seem to buikd pressure even if i pump the brakes. I jsut put a new MC in it this weekend and it didn't fix anything. I decided to remove the prop valve in order to get rid of anything that could go bad. That seemed to help a little bit but I can still push the brakes to the floor and it will barely slow me enough to stop. I have bled these things over and over and over again and i'm positive there is no air in the lines. Has anyone ever experienced this or have any clue what may be causing it? I used to be able to lock all 4 35s on the road but the brakes have just been getting worse and worse to the point where I won't take it on the road. The only thing I can think of the try next is possibly the flexible hose parts of the lines. Maybe they have deteriorated to the point of being able to expand w/ out puttin much pressure on the drums/ caliper.

 

Did you check the apply rod from the booster to master cylinder when you replaced it?
It is adjustable.
Are the rear brakes adjusted properly?

 

yea I extended the rod about 1/4 inch....I didn't know how far to take it any suggestions on how to know how for to make the rod? I adjusted the rear brakes a couple weeks ago too but I'm gonna double check cause i may not have adjusted them far enough.