[mclairmo]

On or more of your rubber brake hoses may be ballooning out when you push on the brakes. This would cause the condition you describe. Check for any bad hoses. Also, unbolt the master cylinder (but do not unbolt/remove the hard brake lines) and then tilt the front of it down with the cap off (so that the front of it is lower than the back of it), but not so much that fluid drips out. Then tap it with a screwdriver or small hammer and see if any air comes out. It's very hard to get all the air out of the master and even bench bleeding may not get it all out. Air can get trapped at the very front of the master cylinder bore since the piston may not go all the way to the front of the bore when you push on the pedal or even when becnh bleeding. Also, be sure the adjusters are clean and greased. Also, may be lousy quality brake pads/shoes that are causing excessive brake fade. Also, be sure there is no grease or brake fluid on the face of the pads/shoes. That will cause the brakes to simply not work. I had slightly leaking front calipers that soaked my pads and I could not stop the car at all. Was very scary. New calipers and pads fixed it. Also, if you have disc brakes, be sure the caliper bleeders are facing up and not down. Good luck.