Finding a Brake Proportioning Valve at Summit Racing

The short answer

You can buy a brake proportioning valve from Summit Racing. The usual starting point is the brake valve category or a search for proportioning valves. Expect two broad groups: adjustable inline valves that go in the rear brake line, and combination valves that bundle proportioning with other functions, such as metering and a pressure differential warning switch. Some listings are vehicle-specific. Many are universal parts that leave it to you to confirm port threads, line size and mounting. Before ordering, know three things: your hydraulic layout, whether each axle uses discs or drums, and what fittings your existing lines use. Each of these is covered below.

How a proportioning valve works

When you brake hard, weight shifts toward the front of the vehicle. The front tires gain grip and the rear tires lose it. With equal pressure at both axles, the rear wheels would lock first and make the car unstable. A proportioning valve passes full pressure to the rear brakes up to a set point, often called the knee or split point. Above that point, it slows how quickly rear pressure rises as pedal effort increases.

An adjustable valve lets you move that point with a knob or lever. This matters when you change tire size, ride height, weight distribution, caliper piston area, rotor diameter or pad friction material. A fixed valve has its setting built in by the manufacturer. Neither type creates braking force. Each one only limits rear pressure so the front brakes do more of the work.

What changes the right choice

Brake layout comes first. A single adjustable valve suits a front/rear split system, where one circuit feeds the rear axle. Many front-wheel-drive and later vehicles use a diagonal split instead, where each circuit feeds one front wheel and the opposite rear wheel. In that layout, a single inline valve cannot balance the rear correctly. The factory design or a professionally engineered solution should guide the decision.

Disc and drum combinations also matter. A car with front discs and rear drums commonly uses a combination valve with a metering section. That section briefly holds off front pressure until the rear shoes contact the drums. After a conversion to four-wheel discs, you may no longer want that metering function, so check whether the valve you pick is designed for disc/disc or disc/drum use. Residual pressure valves are a separate part with a different job, so do not substitute one for a proportioning valve.

Some vehicles already manage rear pressure through ABS, electronic brake force distribution or a load-sensing rear valve, which is common on pickups. Adding an aftermarket valve to these systems is not a simple swap, and it can interfere with the factory controls. Check the vehicle's service information before going further.

Checking fitment before you order

Universal valves still have to match your plumbing, so vehicle fitment comes down to details. Compare the port thread size and flare type in the listing with your brake lines. Inverted flare and AN-style fittings are not interchangeable, and mismatched fittings can leak. Note whether adapters are included or sold separately, and confirm the valve's inlet and outlet direction so it is not installed backwards. Also plan where it will mount. An adjustable valve is most useful where you can reach the knob, but it must sit away from exhaust heat, moving suspension and anything that could strike it.

Read the product description and instructions for the stated applications and any restrictions on use. If a listing is unclear, the manufacturer's instructions or the retailer's technical support are better sources than guessing from photos.

What you can do as the owner

Start with the condition of the rest of the system. A proportioning valve cannot make up for brake pads worn past their wear limits, brake rotors under minimum thickness, a sticking caliper, contaminated friction material or old brake fluid. Inspect these against your vehicle's specifications first, because what looks like a bias problem can turn out to be a hardware fault.

If you install the valve yourself, use quality tubing with correct flares, and tighten fittings according to the manufacturer's guidance. Bleed the entire system with the fluid type specified for your vehicle. On an adjustable valve, begin at the setting recommended in its instructions, then test in a safe, closed area at gradually increasing speeds. The usual goal is for the front wheels to reach lockup slightly before the rears. Adjust in small increments, recheck after each change and record the final setting. If the car pulls or rotates, or the pedal feels soft or sinks, stop testing and find the cause before continuing.

Limitations and when to get help

There is no universally correct valve or setting. The right part depends on your exact master cylinder, caliper and wheel cylinder sizes, tires and vehicle weight, and these vary even between similar vehicles. A parts listing cannot confirm that a valve suits your car's build, and neither can a general guide like this one.

Bring in a brake specialist if the vehicle has unknown previous modifications, or if you notice rear lockup, pulling, fluid leaks or a brake warning light. Braking faults can make a vehicle unsafe to drive, so stop using it until the system has been inspected. For road vehicles, also confirm that brake system changes meet your local inspection requirements.