How are Brake Proportioning Valve issues diagnosed?
A complete brake system inspection is necessary to identify the cause of brake light illumination for these older systems. That is because the most likely cause of the brake warning light is a leak in the brake system allowing a plunger to activate the brake light warning switch. If no leak is visible, bleeding the brakes may be a diagnostic approach used to identify air trapped in the brake proportioning valve due to a period of low fluid in the brake master cylinder reservoir. For all other cases, the technician will notice the performance of the front brakes verses the rear brakes, and may perform a cleaning and adjustment of the rear brake drums before deciding the proportioning valve is faulty. Since a clog may be the cause of the proportioning valve failure, the brakes will be bled to search for restrictions in any of the four brakes, and once any clogs are removed, the system will be closed and tested.
How are Brake Proportioning Valves replaced?
Replacing a proportioning valve requires complete removal of fluid from the brake system, and this will typically be done by suction from all four service brake bleeder valves. This will not only contain leaks, but it will confirm that all contaminated fluid is out of the system. Once the brake system is cleared of fluid, the proportioning valve will be disconnected from the brake lines before removing mounting hardware and fasteners. This will prevent damage and twisting of the brake lines. The new valve is installed in reverse order, and the brake system will be flushed with new fluid, the master cylinder bled, then the rest of the system will be bled of air before test driving the vehicle.
RepairPal Recommendations for Brake Proportioning Valve issues
We recommend using the factory approved brake fluid for the vehicle being repaired, and not mixing any types of brake fluid. Also, the brake system should be flushed and inspected for obvious signs of deterioration, and repaired if necessary to prevent further failure. If the Entire brake hydraulic system is replaced, a new type of brake fluid may be used, but it must be at least the minimum standard of when the vehicle was manufactured.
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What to look out for when dealing with Brake Proportioning Valve issues
Mixing brake fluid can lead to brake system failure due to congealing of the fluid within the brake lines. The different types of brake fluid, i.e. DOT3, DOT4, or DOT5 are meant for higher and higher braking demand, and will not always result in better braking performance. In fact, except for the most strenuous braking conditions, upgrading brake fluid will likely have no benefit.
Can I replace the Brake Proportioning Valve myself?
Proportioning valve replacement is an easy task as long as a good knowledge of hydraulic system maintenance and operation is understood. The informed and experienced DIYer can tackle the diagnosis and repair of the brake proportioning valve in a few hours, but proper bleeding and diagnostic procedures must be understood and followed.