# Brake Systems

### Brakes

#### Brake tech I

Let's start with a slight overview of what a brake system is. That's simply step on the brake pedal and the car stops! Or at least we hope it does. Perhaps if we understand the system a bit more we can get it to work a bit better. We are going to take a big jump in automotive history and start with a single master cylinder four wheel hydraulic brake system. This is the simplest of the modern brake systems. In its simplest you apply force, your foot stepping down on the pedal, to a cylinder full of fluid. Since fluid is not compressible this means a direct 1 to 1 reaction. 1 pound of force in and one pound out. This fluid flows through the steel lines to your wheel cylinders and pushes the pistons out into contact with the brake shoes and they are pushed out to the drums and you stop. Unfortunately it takes a lot more force than 1 pound to stop. So the first thing we do is make a fulcrum out of the pedal, remember Archimedes saying give me a lever long enough and I can move the world? Well space limits the size of the lever but we start there. Next we discover in our physics class that if we take this fluid and push it from a large space into a small space the pressure goes up again. Open the window all the way and you barely feel the breeze, close it almost all the way and the air coming in is quite noticeable. So now we have stepped the pressure up a good bit between the fulcrum of the pedal and changing the size of the outlet on the master cyl. We did loose volume so we can not move the pistons to far in the wheel cyls. But we really do not have to move them to far and remember this is a sealed system so everything instantly moves. Now at the wheel cyl. we make the whole larger again to get more volume and more movement out to the shoes. Also I want to use all that force I developed in the master cyl completely so I use as large a wheel cyl as I can. So now it should work, I have a pedal giving me a mechanical boost in pressure, I use some physics to get even more hydraulic pressure and use nice big wheel cyls to make it all work. Unfortunately I discover that I can not apply equal pressure to both front and rear brakes. Why not? Well, assume the car weighs the exact same front and rear. As you begin to apply the brakes the weight moves forward and lightens the rear wheels and makes the front get heavier. So now I need more force to stop the front wheels than the rear. This is called brake bias. Get it wrong and things get interesting. Remember the VW rabbit when it first came out? It had so much front bias that the back snapped right around in a panic stop. So now we have to add some bias to the system we can do this by changing the size of the wheel cyls. or adding a specially designed valve called a bias or proportioning valve into the system. So now we finally have it down pat. A pedal that I can push without having a leg built like Hercules and just the right amount of pressure at all the wheels to stop in a straight line. Life is perfect! Well not quite, we discover that we need to think about what we used for the brake material and there is also a problem with drums we are finding out about, and one more thing that is such a major flaw in this system that they outlawed single cyl. systems from production in this country in 1968. The tiniest hole anywhere in the system means no brakes any where!