An adjustable brake proportioning valve is used to balance front and rear brake pressures, especially in disc/drum combinations. One is also required in disc/disc applications, considering that 60% of the braking force transfers to the front wheels, and most street rods run big and little tires. 10 lb. residual pressure valve is used to maintain pressure in rear drum brake lines. 2 lb. is used in some factory caliper applications, such as ‘Vette calipers.