Drum & Disc Brake Tech - Whoa, Whoa, Whoa! Photo Gallery
Since '67, all domestically sold vehicles have been equipped with a tandem master cylinder that typically divides the front and rear brakes to provide two separate braking systems (redundancy). To balance braking pressure, most vehicles with front-disc and rear-drum or four-wheel discs use a combination valve and a proportioning valve to bias the front-to-rear pressure, because as a vehicle stops or slows, the center of gravity moves forward. Many performance-brake applications use an adjustable proportioning valve activated by a knob (arrow) to tune the front-to-rear brake pressure.