brakes not working, brake pedal , when depressed, goes to floorboard on 1990 Ford Aerostar

brake pedal, when depressed, reaches the floorboard,,and will not stop readily, the brake fluid is full, and not appear to be leaking. what repairs will need to be done, and what will the expense be, estimate?

Asked by for the 1990 Ford Aerostar
check your wheel cyclinders to see if they are leaking and if they are good its time to replace your master cyclinder, and check on here for the costs they can vary unless you diy then its much cheaper a master cyclinder can run anywhere form 35-150 wheel cyclinders are usually 10-20 a piece, and dont forget to bleed the brakes when you are done
what if you id all that an you still have the problem what you do then?
Definately a Master Cylinder. Just had the exact same problem. New MC brakes are as good as new!
1 more answer
Test the Master Cylinder, have someone depress the pedal with the engine turned on. Watch the MC. If fluid is recycling (fluid level changes with a bubble) then it is your master cylinder. Had the same problem MC replaced and now brakes work fine!