proportioning valve

The Ford Mustang was one of the first cars to offer disc brakes as an option, but they were not a big hit with buyers when they were first introduced. Most buyers were happy to buy a base model with a six-cylinder engine or a slightly improved version with a 289 backed by an automatic transmission. This was the standard Mustang package that most Mustang owners wanted in those days—grocery-chasers that people had no intention of using to sit on the pole of the Indianapolis 500. Aside from the Brickyard, that’s all changed, as standard drum brakes are no longer considered standard fare, and car enthusiasts now know the benefits of full disc brakes. It’s hard to find a car today without them, at least on the front brakes.