BMW 550i xDrive Proportioning / Combination Valve Replacement at your home or office.

What is the Proportioning / Combination Valve all about?

Your braking system relies on hydraulic pressure to operate. When you depress the brake pedal, brake fluid is pushed through the system to the wheels. Fluid pressure is responsible for actuating both disc brake calipers, as well as drum brakes. However, there are numerous components in line between the brake pedal and the brakes themselves, including the combination valve.

The combination valve is responsible for metering fluid to disc brakes, as well as fulfilling tasks done by both the pressure differential switch and proportioning valve (which is responsible for reducing the fluid pressure in the lines leading to the rear drum brakes). This is necessary because of how brakes work in terms of lockup – the more weight there is on a wheel, the more force can be applied without locking up the brakes. In rear drum brakes, the weight on the wheel is comparatively small (the weight of the engine on the front wheels is considerable).