Pulp Friction Page Two
The Master Cylinder
       The next step in the brake system is to convert the amplified force from the brake pedal into hydraulic fluid pressure. The master cylinder, consisting of a piston in a sealed bore with the brake pedal output rod on the one side and brake fluid on the other, performs this task.
       As the pedal assembly output rod pushes on the piston, the piston moves within the cylinder and pushes against the fluid, creating hydraulic pressure. It's really that simple; however, in order to determine how much pressure is generated at the master cylinder, we will need to dig into a few fluid calculations. Don't surf to the classified ads just yet.

       The pressure generated at the master cylinder is equal to the amount of force from the brake pedal output rod divided by the area of the master cylinder piston. If we assume a master cylinder diameter of 0.90 inches (with an area of about 0.64 square inches), the calculated pressure will be 558 pounds per square inch from the 360 pounds of pedal output force from above {360 lbs / (0.64 in. x 0.64 in.)}. Whew, no more math for a minute--just stare at Figure 2 (above) for a while.
       So, does this pressurized hydraulic fluid stop the car? Again, the answer is no, but like the brake pedal, making changes to the master cylinder can impact other characteristics of the brake system.

       Increasing the master cylinder piston diameter will decrease the amount of pressure generated in the fluid for a given input force. In the example above, if a 1.0 inch master cylinder were to be substituted, the output pressure would fall to approximately 450 psi -- a pressure reduction of nearly 20 percent for a O.1-inch increase in diameter. Small changes here make a big difference.

       Decreasing the master cylinder piston diameter works the same principle in reverse. Swapping in a 0.80-inch master cylinder will increase pressure to over 700 psi--this a 25 percent increase for a O.1-inch decrease in diameter.
       Given the relationship between master cylinder piston diameter and hydraulic force, it may seem desirable to use the smallest master cylinder possible. However, since there will always be some compliance (see the sidebar) within the system, the braking system has to have enough additional hydraulic fluid on hand to fill all the extra volume caused by the flexing of components during the compliance phase.
       Unfortunately, this is accomplished by increasing the diameter of the master cylinder-which, we just learned, reduces the pressure generated. Therefore, one has to make sure that the master cylinder has a large enough diameter to meet the fluid volume requirements of the system, but is small enough to generate the pressure required. (There's never an easy answer, is there?)
The Brake Tubes and Hoses
      On the surface, the brake tubes and hoses have one of the easiest jobs in the braking system: transporting the pressurized brake fluid away from the master cylinder to the four corners of the car. It would be ideal to use the most rigid material possible to minimize the compliance in the system. However, since the braking components at the wheels (calipers, pads, and rotors) are usually free to move around with the wheels and tires, a flexible portion is required--and flex equals compliance.

      Traditionally, auto manufacturers have used rigid steel tubing to get the fluid almost all the way there, and a short length of rubbercoated nylon tubing to make the connection to the moving stuff, but even this short section of flexible tubing can cause significant compliance in a racing application.
       For this reason, we racers prefer to replace the rubber hose with a nylon tube covered by stainless steel braiding. Most people notice the reduction in brake pedal travel due to the reduced compliance immediately, but it usually depends on how old and compliant the old rubber-coated hoses were at the time of replacement.

       Although those cool-looking stainless steel brake lines alone will not make your car stop any faster, the decrease in compliance and improvement in pedal feel can make a driver much more confident. They will probably provide some increased level of resistance to damage from flying debris as well. Did we mention they look cool?

The Caliper
       The caliper is one of the most familiar components to the racer, yet sometimes the most misunderstood. Like the master cylinder, the caliper is just a piston within a bore with pressurized fluid on one side. While the master cylinder used mechanical force on the input side to create hydraulic force on the output side, the caliper does the opposite by using hydraulic force on the input side to create mechanical force on the output side. The top view shown in Figure 3 (next page) illustrates how the pressurized brake fluid working against the back side of the piston is converted into a squeezing or clamping force.