Brake Proportion Valves & Balance Bars

What Does a Brake Proportion Valve Do?

A brake proportion valve limits hydraulic pressure to the rear brakes once line pressure passes a set point. That keeps the rear tires from locking before the fronts. It matters because weight shifts forward when you brake, loading the front tires and unloading the rears.

Your front brakes end up doing most of the stopping work. The set point where the valve starts working is called the knee point, or split point. Below it, the front and rear brakes see equal pressure, and above it, the valve passes only part of any added pressure to the rear.

Getting this front-to-rear brake bias right keeps the car straight and stable in hard stops. Too much rear pressure causes early rear lockup and spins, while too little wastes rear braking power. For the other end of the hydraulic system, read our brake master cylinder FAQs or browse all brake parts for your build.

Adjustable vs. Fixed Proportioning Valves

An adjustable proportioning valve lets you dial in rear brake pressure with a rotary knob, while a fixed valve uses a preset ratio. Choose adjustable for custom, street/strip, and race builds. Choose fixed when you want factory-style behavior on a known disc/drum or disc/disc setup.

JEGS offers an adjustable proportioning valve and distribution block with a rotary adjustment valve in black billet aluminum, black, and chrome. Adjustable valve kits add a mounting bracket and brake lines, so you need fewer extra parts. You can also add standalone proportioning valve brackets for a clean install.

Adjustable valves are also available from Wilwood. If you're running one, read how to adjust a Wilwood proportioning valve before your first test stops.

Fixed OE-style valves need no tuning. They only work as intended with the brake combination they were built for, so match the valve to your exact setup.

Proportioning Valves vs. Distribution Blocks, Metering Valves, and Combination Valves

A proportioning valve reduces rear pressure, while distribution blocks, metering valves, and combination valves handle other jobs in the brake circuit. Many OE-style parts combine several of these functions in one housing, so it pays to know what each one does.

Here's how each component works:

• A proportioning valve limits rear brake pressure above the knee point to prevent rear lockup.
• A brake distribution block splits master cylinder output into front and rear lines and often houses a brake warning switch.
• A metering valve briefly holds off front disc pressure so rear drum shoes can overcome their return springs.
• A combination valve packs metering, proportioning, and a pressure-differential warning switch into one OE-style body.

This category includes valves and blocks from Right Stuff, RPC, and Leed Brakes, plus a universal hot rod drum/drum metering valve. Shop all proportioning valves and line locks to compare options side by side.

How to Choose a Proportioning Valve for Your Brake Setup

Start with your brake combination, then match the valve to your master cylinder and line routing. A disc/drum proportioning valve won't give the right balance on a disc/disc car, and the reverse is true.

Use these checkpoints to narrow your choice:

• Disc/drum cars need rear proportioning, and GM disc/drum valve kits mount on the left/driver side.
• Disc/disc systems use an OE-style GM disc/disc valve or an adjustable valve to fine-tune rear bias.
• Drum/drum systems often run a distribution block or a drum/drum metering valve.
• 4-wheel disc conversions call for a dedicated valve, such as a one-piece brass-body unit, paired with drum and disc brake conversion kits.
• Vehicle-specific parts fit 1965-1973 Mustang, 1967-1969 Corvette, 1967-1969 Camaro, and 1962-1976 Chrysler A-, B-, C-, and E-body cars.

Check that the valve's ports match your master cylinder, and browse master cylinders if you're upgrading both. Finish the plumbing with brake lines and brake line fittings in the correct thread size and flare type.

Balance Bars and Line Locks for Race Brake Systems

A brake balance bar is a pedal-mounted bias adjuster for cars with dual master cylinders. It splits pedal force between the front master cylinder and the rear one. Instead of reducing pressure in a line, it changes how hard the pedal pushes each master cylinder.

Race cars with dual master cylinders use balance bars to shift brake bias in small steps without changing the plumbing. Some builds pair a balance bar with an adjustable valve for finer tuning. Make small adjustments and test after each change, since a few turns can noticeably move the bias.

A line lock is a solenoid valve that holds pressure in the front brake lines while the rear brakes release. Drag racers use one to hold the car during burnouts and staging. Browse line lock and roll control kits to add one to your system.