Quote:
Originally Posted by 1948F-1Pickup
.....Residual valves are another (similar) subject. They keep pressure in the lines so that brake fluid doesn't bleed back into the master.... kind of important
with drum brakes because otherwise you'd be left having to pump up the brake pedal to enjoy short pedal travel. Not something you want to need to do.
On disc applications you'll see residual valves mainly if the master is mounted at a weird level, like lower than the calipers.....
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The
main purpose of
drum brake residuals is to keep air from entering past the wheel cylinder cups during release, because of the strong shoe return springs. A
side benefit is a lightly charged fluid line, minimizing pedal movement.
The 2lb
disc residual is
strictly aftermarket, and should
only be used when the master cylinder is lower than calipers, to prevent fluid loss from the calipers.
