Brakes failing.
 

My brakes failed on the way to work. The pedal went to the floor and i had very little braking power. (With the engine off I can build pressure by pumping the pedal.) Kinda scary at highway speed. First I looked for leaks in the system. No visible fluid leakage. I don't think the booster is bad ( i think failing booster makes the pedal stiffer, not soft). No sign of vacuum leaks. No hissing from the line to booster. Could there be air in the lines? How would it get there with no leaks? Reservoir is full and shows no sign of losing fluid. Or is my master cylinder failing?

Any help is appreciated.

Please read the forum rules, you must wait 24 hours of no responses before you bump your thread.

That being said

If there is no signs of losing fluid, i would say the master is going bad, or is bad.

^ Dito

If the red "BRAKE" light on the dash is illuminated, and the parking brake is fully released, there's a leak.

I have inspected every line and brake assembly looking for fluid and have found none. Could there be a leak letting air in without leaking fluid?

To let air in, it would have to push fluid out first. Then when you release the pedal, it would suck air in. Is the red light on?

Yes. Could there be fluid leaking somewhere not visible by following every line to their end? The lack of a visible fluid leak is what has me stumped.

There are only two things that turn that red light on: One is the parking brake and the other is the centering valve. The centering valve is designed to shut off fluid flow in the event of a pressure loss in either of the hydraulic systems, (front or rear). It happens instantaneously when you apply the brake pedal if there's a leak, so you may have to look closely to find it. The steel line that runs along the frame to the rear flex hose is the most common place. Usually at the plastic brackets that hold the line in place along the frame.

Ok. I found an area on the line to front passenger side that may be the culprit. It's hard to tell because it's covered in grime and oil from a previous incident, but it's the only wet spot i can find. I did observe that with the cover off of the reservoir when i step on the pedal i can see fluid being pushed out of the rear portion but not the front. Would that indicate that the centering valve is stopping flow to the front lines, reinforcing the idea that the leak is in a front line?