Help with the brakes

Mcgingy306

Hey guys, i'm relativity new to older cars and cars in general but i have a 1975 GMC suburban that has a problem i cannot quite locate. when the car is off i can pump the breaks and the first couple times it sounds like air is coming out of the break pedal or around it and then it builds up a slight amount of pressure. after i turn the engine over the breaks build no pressure at all and im left with the air sound. when driving i have no break at all when pushing the petal down up until the very last inch or so then it breaks rather slowly. i have yet to bleed the breaks but i havent done any break work on the car so i do not know how air would have gotten into the lines in the first place. Any help is great help, thank you in advance.

Mcgingy306

it went down hill in just about two days the break pedal had about three quarters of the pedal working then half then about an inch. the only work i have done on it in that time period was replace a gas hose because it had a leak. i have never replaced the break pads but i also dont think they would deteriorate within two days. i did upgrade the carburetor from a quadrapuke to a edelbrock two months ago with no loss to break power then.