Proportioning valve problems

The brake proportioning valve on an automotive vehicle serves a very important function in the braking system. Vehicles with front disc and rear drum brakes have proportioning valves located on the brake line between the front and rear brakes. The proportioning valve , also called the combination valve , is located in the disc braking system. It is responsible for controlling the braking pressure between the front and rear brakes. The front bowl is for the front brakes for front disc brakes - consider the size of the pistons in the front calipers.

As the pads and rotors wear, it will take a tremendous amount of fluid to displace the front pistons with their large bores compared to the relatively small pistons in the rear wheel. They combine the functions of both a metering valve and a proportioning valve with the addition of a brake light warning switch. The brake light warning switch signals when there is an imbalance of pressure in the system caused by a problem in the front or rear brakes. The button on the front of the valve is to open the back door in the metering valve for the disc portion.

The metering or delay valve in the disc side of the combo valve prevents pressure from being delivered to the front brakes until it is high enough to overcome the tension of the springs on the drum half of the system. It contains a proportioning valve which reduces pressure to the back brakes during a panic stop and a metering valve which lowers front brake pressure during initial brake operation. So your problem could be with the metering part of the combo valve. I took the switch out, and the plunger is pretty stiff, but it moves in and out. In the process of natural operation, the fluid flows back and forth through this valve.

As the system wears, particulate matter begins to develop, and tends to gather at the orifices there. Usually a back-flush will clear this out. With an adjustable proportioning valve , you can slow down the pressure rise that occurs when you apply the brakes. They provide balanced braking during sudden, hard braking by restricting fluid pressure to the rear brakes. Cause: Not have an understanding of what the proportioning valve does and when it does it.

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We know our parts and products. But as soon as I give a normal application (about inches in length) the light goes back on. I disconnected the wires into the top of the porportioning valve and PRESTO the light problem ended completely. This tells me that the problem is in proportioning valve.

Any ideas or old stories on how to reset this valve back to normal. ProbleDetermining when and why to add the proportioning valve (s) to the list of possible causes of the problem being diagnosed. It seemed like the rear cylinders might have been sucking air back in but I am not sure. If the proportioning valve were set to percent and the brake pressure were 0pounds per square inch (psi) for the front brakes, the rear brakes would get 7psi.

Well, under normal braking use, the poppet of the proportioning valve sits dormant and does nothing. The adjustable proportioning valve is used to set rear brake pressure to reduce rear wheel lockup on front wheel drive vehicles. This valve is known as the adjustable proportioning valve. Re: Load sensing proportioning valve removal ? From the “T” fitting, the front lines are then split off to the left and right calipers.

GM brake proportioning valves to fit your Chevy, Buick, Oldsmobile, Pontiac and Chevy Trucks and Vans.

Proportioning Valve Plumbing The most common proportioning valve plumbing is shown below. These problems are solved with use of the bob-tail proportioning valve and the bob-tail ratio valve. Bendix LQ-Bob-Tail Ratio Valve. It must reduce the percentage of front wheel brake air pressure when a trailer is attached. An adjustable proportioning valve has a single inlet and outlet and is plumbed only in the rear tubing.

If your front tubes go to it, it is a combination valve and much more complicated. Classic Performance brake proportioning valves are designed to ensure that proper brake fluid pressure is supplied to the front and rear wheels. These valves are available in both fixed and adjustable versions for drum to disc brake upgrades. The brake light will come on for two reasons: the switch on the parking brake lever, or the slider in the combo ( proportioning ) valve.

The slider is meant to detect a major pressure difference between front and rear, i. Register Stovebolt. Forums The HiPo Shop How to adjust proportioning valve. Brake Differential Proportional Valve Problems in popular cars Brake Differential Proportional Valve problem is a common vehicle problem that happens to most car brands and models. My Allante has dual proportioning valves , one going to each rear wheel.

I took one apart and the only possible leak path was an easy-to-replace O-ring. Combination valve mounted: The last proportioning valve type is the combination valve. You can also use an adjustable proportioning valve with the bracket that mounts under your exsisting master which would be less $$. So far this has fixed my problem. When we get piled upon one another in large cities, as in Europe, we shall become as corrupt as Europe.

It may be used with either a manual or power booster setup. On my Wilwood valve , screwing the knob clockwise increases rear brake, CCW decreases rear brake. Could this have anything to do with the proportioning valve ? ADJUSTABLE PROPORTIONING VALVE INSTRUCTIONS IN = Line from Master Cylinder OUT = Line going to rear brakes 1. Turn valve to full increase.

Increase the valve half to number of turns counted in step 2. This is your start point for adjustment.