How does the proportioning valve on a master cylinder work?
How does the proportioning valve on a master cylinder work?
If equal braking force were applied to all four wheels during a stop, the rear wheels would lock-up before the front wheels. The proportioning valve only lets a portion of the amount of pressure to the rear wheels thus preventing rear wheel lock-up.
Where is the proportioning valve on a car?
The proportioning valve is mounted between the brake line master cylinder and the rear wheels. It’s designed to adjust the pressure between the front and rear brakes, depending on how hard you’re stopping. The shorter the stopping distance, the more of the vehicle’s weight is transferred to the front wheels.
How does pressure build in a master cylinder?
When the brake pedal is depressed, it pushes on the first (primary piston) through a linkage. The Pressure builds in the cylinder and lines as the brake pedal is depressed further. The pressure between the primary and secondary piston forces the secondary piston to compress the fluid in its circuit.
What are the symptoms of a bad proportioning valve?
If you suspect there is an issue with your proportioning valve, check for the following symptom: Rear wheels lock up Since the proportioning valve decreases the pressure sent to the rear brakes, the main symptom the valve is going bad is the rear wheels locking up when the brakes are applied.
Is the proportioning valve part of the master cylinder?
Vehicles with front to rear split hydraulic systems have one while diagonal splits system require two because each rear wheel is on a separate hydraulic circuit. The proportioning valve may be a stand alone valve, part of the combination valve or built into the master cylinder. (See pg 82 for valve identification)
How do you get a proportioning valve to work?
Bleed the rear brake line again at the proportioning valve, as you did before if you still have a brake dash light. Bleed the front brake lines on the proportioning valve in the same fashion. This reversal of pressure will eventually break the spool loose inside the proportioning valve, equalizing the pressure between the front and rear brakes.
What to do if your brake proportioning valve is stuck?
Depress the brake pedal and note if you have a brake light on the dashboard. If your brake system has not been previously worked on or suffered no brake leaks from the wheel cylinders, calipers or master cylinder, chances are the brake proportioning valve is stuck in one position, tripping the brake dash light.
Which is the best way to diagnose a failed proportioning valve?
Most shops do not have pressure gauges so the process used to diagnose the problem will have to be a process of elimination. All other possible causes will have to be checked before the proportioning valve is condemned. Pressure gauges are the best way to diagnose a failed proportioning valve.
