I have a 76 c10 2wd with manual brakes, and a problem i'm not sure how to diagnose. Recently when i will press my brake pedal to stop it will go most of the way down with no pressure and then there is some pressure in the last little bit of pedal travel. Sometimes if i just pump it i will get the full pressure back, and sometimes i have to pull the pedal up quickly with my left foot and press again to get good pressure. The pedal will usually return to normal position on its own after a couple seconds without pulling it up, but when driving obviously it is not smart to wait on that. I would say I experience this problem about 70-80% of the time while driving. I have not found any leaks yet, and no change in fluid level (although a bit low, i assume from normal pad wear). Could it be that I'm too low on fluid, or need to bleed the brake system? Or do I need to look into getting a master cylinder?