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A good brake system is not only a life-saver, but it can change your car’s braking characteristic from a routine driver into a great performing street rod. A few items like a spring-loaded brake proportioning valve and adjustable or non-adjustable metering valves can make all the difference in the world. 

In a recent article on Speedway Motors tech blog The Toolbox, the subject of What Your Brake System Needs, regarding valves, was covered. We are condensing the highlights of Eric McMillan’s article below. The full article can be viewed by clicking on the link above. 

By this point, everyone agrees that disc brake conversions are the way to go for anyone regularly driving a vintage car that was originally equipped with drum brakes. Modern speeds and traffic make this a safety issue. With so many different cars and conversions, there is no “one size fits all” solution. McMillan smartly points out the requirements for upgrading the brakes on a ’32 coupe are very different than installing power brakes on a ’69 Chevelle. 

Universal adjustable proportioning blocks with brake light switch.

“You must consider things like front and rear weight bias, tire size (the contact patch of the tire determines the braking effectiveness of your brake system), caliper and wheel-cylinder capacity, and more,” McMillan writes. If this were not enough to cause confusion for some, figuring out how to “tune” the brake system with the correct sized booster, rotor diameter, and caliper can really turn into a puzzle.

Finally, when enthusiasts have their heads wrapped around all those components of the brake system, the brake proportioning valve for metering and pressure comes into play. These are often misunderstood components, but understanding them can mean the difference between a confident push on the brake pedal or a weak feeling pedal. 

Mcmillan explains what a residual-pressure brake valve is, and the different pressure-rated valves used in most brake upgrades. “A residual pressure valve will hold a small amount of fluid pressure in the brake system when the brake pedal is in the fully retracted position,” he states.  “The purpose of this is to eliminate the possibility of fluid transferring from the caliper or wheel cylinder back into the master cylinder reservoir.” 

Wilwood Residual Pressure Valve and Fittings Kit.

Keeping some residual pressure in the system helps maintain a brake pedal that is firm and ready to function when engaged. The two most common pressure ratings used in these valves are 2-psi and 10-psi. The 2-psi valve is used for disc brake calipers and the 10-psi valve is commonly used for drum brakes with wheel cylinders. The reason for the different pressure ratings is the required amount of pressure to initiate braking in the different brake systems. McMillan explains the reasoning behind these differences in the full article. 

Wilwood part #260-11179 adjustable proportioning block.

A brake proportioning valve, sometimes called a brake bias valve or metering valve, is designed to balance out the braking between the front and rear brakes based on need. A properly balanced system will stop a car quickly and safely. An unbalanced system makes the car unstable and will likely spin or lock up the brakes and skid. A brake proportioning valve is always required in an automotive brake system that uses dissimilar styles (disc/drum). McMillan points out sometimes these “valves have other features, like brake light pressure switch or an adjustable rear circuit.” A proportioning brake valve with multiple features is often referred to as a combination valve.

GM Disc/Drum Proportioning Valve offered by Speedway Motors.

To understand more about residual pressure valves and the brake proportioning valve, the different types, and how to adjust them, visit Speedway Motors online at www.speedwaymotors.com.

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