1987 Mercury Station Wagon V8 Two Wheel Drive Automatic 117249 miles
I have a Grand Marquis that when I step on the brake, It goes to the floor when the engine is running, when the engine is off, the pedal is " tight" hard to push to the floor. I replace the Master cylinder, Bleeds the lines on all four wheels and check the " Vacuum check valve" which is o.K.
If you have checked for, and found no leaks, check the fluid level and condition, you may have contaminated fluid, put some fluid from the master in a cup of water, swirl, it should turn milky white, with no oil beads floating on top. If any beads, the fluid is contaminated with oil or tranny fluid! This would require the replacement of ALL rubber brake parts, calipers, Master, wheel cylinders and hoses, then you would need to flush the steel lines with alcohol or brakekleen. If the test is normal, get some brass plugs, and remove the steel lines at the Master, install and tighten the plugs, does the pedal behave normally? If not replace the Master. If it does pump up and remain high, your leak is in a caliper or wheel cylinder.A dead giveaway to contamination is a swollen rubber seal on the master cylinder.