My mother-in-laws car has had some serious problems with the wheels locking up. After replacing the brakes, rotors, etc. She was told by a mechanic that the only thing left to check was the proportioning valve. Where would we find the proportioning valve and does anyone know how we would go about changing it? Thanks!
Usually if the car has a valve it is mounted on the firewall. But your master cylinder has 4 connections, one for each wheel. So I doubt your car has a separate proportioning valve. You could check with the dealer to verify.
SOURCE: Brakes no longer work in 1989 Chevy half ton pickup 2 wheel drive 350cubic inch
change dump valve under master cylinder
SOURCE: 1989 chevy caprice proportioning valve
The proportioning valve can be mounted on the frame or just off of the master cylinder. Yes, you can buy aftermarket and no you don't have to stay OEM on it.
SOURCE: Where to find.a proportioning valve
It should be on the frame below the master cylinder. Just follow your brake lines off of the master to a block with a wire plug.
SOURCE: The brake light is on
The proportioning valve simply ensures that the front brakes are applied before the rear brakes are, to prevent sideways skids from loss of rear traction. The valve also serves as a warning light when one end, either front or rear, of the system has deficient line pressure. Inside the valve is a cylinder, and a piston that belongs in the center of the valve cylinder (when fluid pressure on each side is equal). When one side of the valve (front or rear brake system) loses pressure (like from a leaking brake line), the piston gets pushed to the low pressure end and makes contact with a switch terminal that turns the light on.The trick to turning the light off is to figure out which end, front or rear brakes, the piston is on, and then bleed the other end to center the piston and turn the light off. Too much pressure on the brake pedal will cause the piston to go past center to the opposite end, and a close watch on the brake warning light will reveal that as the lamp will flicker once while the piston passes center.
Gently depress the brake pedal (requires an assistant) with a bleeder open and close the bleeder as soon as the assistant (brake pumper) sees the light go out. If he sees the light flicker once bleed the other end of the vehicle to go back towards center.
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