I have a 02 Mercury grand Marquis GS with abs Some how the brake line had a rust hole in it and broke right in the center it's the line that's above the fuel tank goes for left to right Not sure if the master cylinder went empty and all the fluid had leaked out someone that wanted to buy it was test driving it when it broke well anyway I changed the brake line and filled the m/c with brake fluid bled all the brakes by having a friend pump them up and hold while i crack the banjo bolt on each wheel cause bleeder screws are frozen and I didn't want to break them off and have bigger problems did this 5 times on each wheel and made sure m/c was topped off and didn't go low on fluid while I was bleeding each wheel afterwards I went to test drove it and noticed when you go to stop pedal is very soft and goes to the floor but if you pump the the pedal then it still goes to the floor and you can stop the car I checked the m/s and it's full and there is no leaks all the lines are dry no fluid leak anywhere that I can see there's no brake light or abs light on in the dash..I'm puzzled I don't think it's my brake booster could it be the m/s ? Any true no what there talking about mechanics here that had this problem with the Marquis

 

You can't successfully bleed the brakes at the banjo, air will get trapped within the caliper.. You need to open the bleeder screws to do it right. Several things to consider here. If a line was replaced, you need a scan tool to activate the solenoids in the ABS unit to expel the air in it. Also, when bleeding, you never want to push the brake pedal down to the floor while bleeding. During many years of use, the bore within the M/C will develope a ridge. By pressing the brake pedal down to the floor, you push the rubber seals over that ridge, possibly destroying them. You then have a bad M/C which will be internally bypassing fluid.

 

If most of the fluid leaked out of your brake system, then I'm wondering if the plunger inside the master cylinder may have been able to travel further than it should have, when you stepped on the brakes, and now as a result, the plunger isn't working properly, and you cannot bleed properly? But as the above person said, you should bleed from the bleeder valves, and not from the banjo fittings. Anyway, your master cylinder is now several years old, and it is suspect, so I would replace it.