Proportioning Valves
Find brake proportioning valves and related components for classic cars, trucks, restorations, and brake conversions. Explore fixed and adjustable valves, combination valve kits, residual pressure valves, distribution blocks, fittings, brackets, and installation accessories.
Proportioning Valves and Hydraulic Brake Control
Front and rear brakes do not always need the same hydraulic pressure. That difference becomes especially important after a disc brake conversion, where the front and rear circuits may now be using completely different brake hardware.
A fixed combination valve handles that relationship around a defined brake setup, while an adjustable proportioning valve lets rear pressure be reduced or tuned when the vehicle needs more control over brake balance.
Other parts in this collection deal with what happens elsewhere in the hydraulic circuit. Residual pressure valves help manage fluid return, metering valves control when pressure reaches part of the system, and distribution blocks route fluid between circuits while supporting warning-light functions on certain applications.
Brackets, pre-bent lines, fittings, and bleed tools then handle the physical side of integrating those controls around the master cylinder. GM AC Delco-style assemblies, Ford-specific kits, and OE-style Camaro, Corvette, and Mustang components each approach the same hydraulic system from a different point.
FAQ
How do I choose the right brake proportioning valve?
Start by identifying whether your vehicle has front disc/rear drum brakes or four-wheel discs. Then check the master cylinder, mounting location, brake-line connections, and whether you need a fixed combination valve or adjustable proportioning valve. Some products in this collection are designed for specific GM or Ford configurations, while others provide more adjustment for custom braking systems.
What is the difference between a proportioning valve and a combination valve?
A proportioning valve primarily controls hydraulic pressure to the rear brakes to help maintain suitable front-to-rear brake balance. A combination valve can combine several hydraulic functions into one assembly, depending on its design. POL's AC Delco-style combination valves also incorporate a pressure-differential safety function that can isolate part of the braking system if a loss of pressure occurs.
Should I choose a fixed or adjustable proportioning valve?
A fixed valve is designed around a particular brake configuration and can be a practical choice when the braking system closely matches that setup. An adjustable proportioning valve lets you fine-tune pressure to the rear brakes, which can be useful on custom or modified vehicles where brake components, tire sizes, weight distribution, or other factors differ from a factory configuration.
Do I need a different proportioning valve for disc/drum and four-wheel disc brakes?
Yes, the valve should be selected for the brake configuration being used. A front-disc/rear-drum system has different hydraulic requirements from a four-wheel-disc system. Several kits in this collection are offered specifically for two-wheel or four-wheel disc configurations, so confirm the brakes installed at both axles before ordering.
What is a residual pressure valve, and do I need one?
A residual pressure valve maintains a small amount of pressure in part of the hydraulic system and can help reduce brake fluid bleed-back. Whether one is required depends on the brake type, master cylinder location, and overall hydraulic setup. POL offers different residual pressure valves, including 2-, 4-, and 10-pound options, so the pressure rating should be matched to the specific application rather than selected by size alone.
What is the difference between side-mount and under-mount proportioning valve kits?
The difference is where the valve and bracket are positioned in relation to the master cylinder. Side-mount kits position the valve alongside the master cylinder, while under-mount versions place it underneath. POL offers both configurations for compatible GM-style master cylinders. Available space, brake-line routing, master cylinder design, and the appearance you want can help determine which arrangement is more suitable.
What does a proportioning valve bleed tool do?
POL's GM proportioning valve bleed tool temporarily replaces the warning-light switch during brake bleeding. It holds the low-pressure shutoff valve in position so the system can be bled without repeatedly removing the switch and recentering the valve. It is designed for popular non-adjustable GM-style combination valves, including compatible AC Delco configurations.