Product Profiles

Brake Proportioning Valves 101: How They Work & Which Style to Choose

(Image/Thirdgen.org)

Brake proportioning valves are the parts of a vehicle’s brake system that limit the amount of pressure reaching the rear brakes, which helps to prevent rear wheel lock-up, allowing you to stop your vehicle more safely and efficiently.

Whether your vehicle has rear disc brakes or drum brakes, the rear brakes require less pressure than the front brakes, which is why the brake proportioning valves exist, and why they’re so important.

There are three common styles of brake proportioning valves.

1. Fixed Proportioning Valves

(Image/Team Grand Wagoneer)

This type of valve is not adjustable. Fixed proportioning valves are typically used in stock applications, or in applications that fit specifically to a particular brake setup.

2. Adjustable Proportioning Valves

(Image/For A Bodies Only Mopar Forum)

This type of valve—as the name suggests—is adjustable. Adjustable proportioning valves are typically used in an aftermarket brake system where the vehicle owner might need to adjust the braking pressure going to the rear brakes.

3. Lever Proportioning Valves

(Image/Wilwood)

Lever proportioning valves are also adjustable, but use a lever rather than a turn knob to adjust the rear brakes. These types of valves are typically ran in line with the rear brake lines.

Brake proportioning valves work exclusively with rear brakes. They do no proportioning on front brakes. Most proportioning valves sold today also include a brake light switch.

Summit Racing tech adviser Mark Lake contributed to this report.

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2 Comments

  1. Frank Madonia says:

    You may want to rethink and clarify your advice that: “Brake proportioning valves work exclusively with rear brakes. They do no proportioning on front brakes”.

    The below advice from Strange Engineering pertains to proportioning valves in most drag race applications:

    Brake pressure should always be checked with a brake pressure gauge before use. In disc brake applications used for drag racing only, front brake pressure should be 550 to 650 lbs and rear brake pressure 1,000 to 1,100 lbs. These pressures should be achieved with a lot of effort since they are at “lock-up” of the tires and the actual normal stopping pressures will be lower.
    When calipers or master cylinders are changed in an OEM system, the stock proportioning valve should be removed in favor of an adjustable proportioning valve. In most drag racing applications, it should be plumbed between the master cylinder and the front calipers to limit pressure. For street applications, or a system using disc front / drum rear, the proportioning valve
    would be plumbed between the master cylinder and the rear brakes. In either application, adjustments should be made to the valve in order to achieve the same braking threshold for front and rear brakes.

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