Proportional Valves:  Proportional valves are used to regulate the pressure in the line.  The Wilwood valve shown here, has an adjustment range of 100 to 1,000 psi.  It can decrease your line pressure up to 57 percent.  It is generally used on the back brake to adjust the balance between the front and rear brakes.

You NASCAR car fans can relate to over braking by the rear wheels.  Remember the drivers on the short tracks that forgot to change the balance bar before ending the pits?  Yes, they did spun out. 

This is one of the reasons a proportional valve should come free with every brake kit sold.  If it is free you will install it, if it is not free you might not buy it.

Residual Valves: Residual valves are pressure valve use to retain pressure in the lines.  The most common use is on a hotrod when there is a floor mounted brake pedal and master cylinder.  Mounting the master cylinder (M/C) below the floor positions it below the calipers.  Gravity will cause the fluid to flow away from the calipers.  The residual valve will retain pressure within the lines.  (i.e. 2 pounds residual valve will retain 2 pounds of pressure, 10 pound will retain 10 pounds.)  Drum brake master cylinders have residual valve(s) built into the master cylinder.  This is needed to maintain pressure against the cup seals in the wheel cylinders.  If you are using a disc brake master cylinder or after market you will need to install a 10 pound residual valve for the drum brakes.  Do not install a residual valve if your master cylinder already has one in it.  This will cause the brakes to lock up after the second application to the brake pedal.  

Distribution Blocks or Combination Valves:  One of the biggest misconceptions is the distribution block or combination valve.  Almost every factory car has one.  This usually serves as a metering block to adjust the proportioning to the rear brakes, as a "T" fitting for your front left and right front brake lines and brake light warning switch.  What people fail to understand is that each car is "engineering" for a specific distribution block based on weight, braking characteristics and tires.  So generally most factory cars have different blocks.

Ask yourself this.  How can one distribution block be engineered for all applications?  So, we have this 23T with tiny tires in front and big tires in the back, we have a 57 Caddy and a 57 Chevy pick up.  Do you really think the braking is the same for all three vehicles?

Save yourself some headaches install a adjustable proportional valve in the rear brake lines.

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