[kenny-1907]

If it was working after you changed it and now it has stopped , most likely it is the master cylinder. some things just don't pay to get from a scrap yard. Air in the lines would cause a spongy pedal and leaks of that amount to cause a pedal to go all the way to the floor you would think you would see, and a bad power booster causes a extremely hard pedal. Just bear in mind that you can get a faulty remanufactured master cylinder as well. Quite a few years back i used to own a 68 dodge dart and the master cylinder went on it so i went to crappy tire for a reman one. To make a long story short , the sixth one worked , all the others were bypassing as soon as they were bench bled and installed.