Adjustable Brake Proportioning Valve ~ What It Does and Why You Need It

Adjustable Brake Proportioning Valve

Matthew Finlay is working to finish up his disk brake conversion. He’s got everything installed — behind the dash master cylinder/booster combo, front/rear rotors installed, Wilwood dual-piston calipers, and all braided steel lines.

But something didn’t feel right…

It seemed like there was an odd amount of travel on the brake pedal but it didn’t feel like air and no amount of bleeding helped. The master/booster is mounted low on the firewall, and combine that with an air ride suspension — fluid just doesn’t want to flow out to the calipers.

To fix this, Matthew installed a Baer Brakes residual valve. He feels like the brand doesn’t really matter here, but he appreciated Baer’s 3AN version because he could plumb it into the brake lines without adding extra adapter fittings.

He points out that another way to adjust bias is by installing different types/grades of pads but warns to be very careful when swapping so that you stay with pads in the correct heat ranges and usages. He’s been around cars with mismatched brake pads and they will start doing really weird things and should just be avoided unless you have a plan in place.

It’s a good idea to talk to manufacturers as they can recommend different brake pad compounds that will work together.

Matthew bought a cheap IR thermometer to do some before and after brake temperature testing. He drove around his neighborhood and checked the front and rear rotor temperatures. His initial guess was correct that the front rotors weren’t doing much and were basically “along for the ride”.

After messing around with the proportioning valve adjustment knob, Matthew ended up dialing the brake bias all the way down on the rear. The testing route was just over 2 miles of normal city driving with a maximum speed of 35 mph while attempting to brake the same as the previous attempt.

He got much better results this time. Not only did the car feel better stopping it was braking like a normal car. Remember — you NEVER want the rear of the car locking up before the front.

What is a Brake Proportioning Valve?

A proportioning valve is a valve that relies on the statics to supply reduced pressure to an output line. A simple example is where spring load applies a reducing force so that the output pressure is reduced. Proportioning valves are frequently used in cars to reduce the brake fluid pressure to the rear brakes.

Parts Used

Proportioning Valve, 3/8-24 in Inverted Flare Female Inlet, 3/8-24 in Inverted Flare Female Outlet, Adjustable 100-1000 psi, Knob Type, Aluminum, Each

The new generation of adjustable proportioning valves combines the latest refinements to deliver precise pressure metering and strength from a compact forged billet design.

Pressure adjustments range from 150-1200 PSI and provide for a maximum decrease of 57% in line pressure, the most of any available valve.

An adjuster knob with fine thread tuning provides precise pressure adjustment. This adjustment lets you fine-tune the front to rear braking balance by proportionally decreasing the rear brake line pressure. Valves weigh only 5.2 ounces and have two .25″ side mounting holes spaced 1.00″ apart.

This valve varies from our standard Knob Style Proportioning valve, as the in and out ports are 3/8-24 inverted flare seats and do not require tube nut adapters to directly install 3/16 tubing with inverted flare 3/8-24 nuts.