Jim Grant's Tech Tips
'97 Mercury Sable GS Wagon, Fade Away Brakes
brake problems with my '97 Mercury Sable GS Wagon, 3.0, V6, FWD. I bought
it from a used car dealer a few months ago. Now the brake pedal goes to
the floor intermittently. The master cylinder fluid level has never gone
down. There are no signs of leaks. The vehicle has not been modified.
Could it be the proportioning valve?
is very unlikely that the proportioning valve is the problem. The proportioning
valve doesn't do much under normal braking conditions. It is when you
step on the brakes quickly that the valve slows the flow and pressure
to the rear brakes. This is done to reduce rear wheel lock-up under panic
braking conditions. A brake pedal that randomly fades away with no brake
fluid loss, I would be inclined to suspect a failing brake master cylinder.