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


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.