GM Style Brass Proportioning (combination) Valve
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Brass Proportioning Valve
This is for Disc/Disc Applications. (We also have Disc/Drum proportioning valves- please see our Ebay store). In this combination valve you have two valves in one: a Proportioning valve and a metering valve! For more information see the plethora of info below! |
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Frequently Asked Questions Valving
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Question
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Answer
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| What does a proportioning valve do? | A proportioning valve is used in the rear to decrease the rate of pressure rise to the drums relative to the pedal force as weight is shifted to the front during braking. This prevents the rear from locking up under hard braking conditions. |
| What are the symptoms of a bad proportioning valve? | If your prop valve has gone bad your rear wheels will lock up easily, especially on wet surfaces. |
| What does a metering valve do? | A metering valve or "hold off valve" is used in the disc portion of a disc/drum system to hold off the application of the front discs slightly allowing the slower reacting rears to catch up. This provides rear stability on wet surfaces and reduces excessive pad wear. |
| What are the symptoms of a bad metering valve? | Your car will nose dive and the front pads will wear too fast. |
| What does a residual valve do? | There are two different uses for residual valves. The 10 lb valve is used to hold a residual pressure to the drum brakes to give a higher firmer pedal. The 2 lb valve is used in the disc when the master cylinder is lower than the calipers to prevent back siphoning of the fluid from the master. |
| What are the symptoms of a bad residual valve? | The brakes will be very spongy and you will need to pump the pedal to get good brakes. |
| What is a combination valve? | A combination valve incorporates metering and proportioning into one valve providing all necessary valving for disc/drum systems. See below |
| Should I use an adjustable proportioning valve? | Not if you can help it. The adjustable valve will only provide the proportioning function and not the metering that is needed. |
VALVE TYPES
| VALVING | DESCRIPTION |
| Metering | The metering or hold off valve is used in the brake system to better balance the front to rear brakes. The valve does not allow the pressure to rise at the front disc brakes until the pressure at the rear drums has risen sufficiently to overcome the brake shoe springs. At this point the valve opens to allow full pressure to build at the front brakes. |
| Proportioning | The proportioning valve modulates the pressure to the rear brakes. The modulation is necessary to minimize rear wheel lock up found in heavy braking and to compensate for the differences in braking conditions in front disc / rear drum systems. As pressure is applied to the system full pressure is allowed to the rear drums up to a certain point. Beyond that point the pressure to the rear is reduced preventing rear brake lock up. |
| Residual | There are two different residual valves. A ten pound residual valve will maintain a line pressure to the rear to keep the drum brake shoes out close to the drums giving a higher firmer pedal. Without a ten pound residual pressure to the rear you will experience a spongy pedal. A two pound residual valve is required whenever the master cylinder is lower than the calipers to prevent backflow of fluid from the calipers to the master. |
| Combination | A combination valve incorporates metering and proportioning into one valve. These are available for disc/drum or drum/drum systems. |
| Adjustable Prop. Valve | The adjustable proportioning valve is used when you have a special rear condition that requires higher or lower pressure than a normal condition. You sould always use a metering valve to the front when using the adjustable |
CORRECT VALVE INSTALLATIONS
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DRUM BRAKES FRONT AND REAR WITH MASTER ON FIREWALL OR UNDER FLOOR
Drum brakes require a 10 lb. residual pressure (RPV10) to counteract the spring tension in the drum system which tends to pull the shoes away from the drums. This will give you a longer pedal travel and "spongy" brakes. The residual valve holds a pressure keeping the shoes near the drums giving a higher firmer pedal. Also required a metering valve (PVM) to the front (the metering valve prevents nose dive). |
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DISC BRAKES FRONT AND DRUMS REAR WITH MASTER ON FIREWALL
A disc/drum combination valve (PV2) is the easiest way to properly balance your braking system. The combination valve is two valves in one. It provides metering to the front which prevents nose dive and proportioning to the rear which prevents rear wheel lock up. We also recommend the addition of a 10 lb residual valve (RPV10) to the rear drum brakes. |
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DISC BRAKES FRONT AND DRUMS REAR WITH MASTER UNDER FLOOR
The best way to plumb a disc/drum system when the master is under the floor is with a combination valve (PV2) and then a 2 pound residual valve (RPV2) to the front which is needed to prevent fluid from flowing back from the calipers into the master. We also recommend the addition of a 10 lb residual valve (RPV10) to the rear drum brakes.
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DISC BRAKES FRONT AND DISCS REAR WITH MASTER ON FIREWALL
The best way to plumb a disc/disc system when the master is on the firewall is with a four wheel disc brake combination valve (PV4). |
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DISC BRAKES FRONT AND DISCS REAR WITH MASTER UNDER FLOOR
The best way to plumb a disc/disc system when the master is under the firewall is with a four wheel disc brake combination valve (PV4) and a two pound residual valve (RPV2) to the front and a two pound residual valve (RPV2) to the rear.
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