While fixed calipers are very effective, they do have a couple of minor shortcomings. First off, since there are pistons on both sides of the caliper, fluid must be delivered to both sides of the caliper. That means small external lines or well-sealed interior passages must be provided to connect the two halves. In either case that means that construction is more complicated and consequently, more expensive.

And while they perform very well, they are unforgiving of any runout in the rotor. If the rotor wobbles it will tend to make the brake pedal pulsate on application, and in the case of a badly warped rotor the pistons can get knocked back into the caliper body. When that happens more fluid will be required to apply the brakes, which means the brake pedal will have to travel farther.

Another caliper design is the sliding style. These have a single piston on just one side; working like a C-clamp, as the piston pushes the inside brake pad against the rotor. Once it makes contact, the caliper slides in its bracket and pulls the outside pad against the rotor. Ford and Chrysler used this style caliper.

Similar to the sliding caliper is the floating design (typically single-piston GM calipers). Like the sliding caliper, floating calipers apply hydraulic pressure to one pad, then the caliper, which "floats" on a pair of mounting pins, pulls the other pad against the rotor. While the sliding and floating calipers work in a similar fashion, there is one major difference. With the sliding style the braking force is transferred to the caliper, which means it must be a stout piece. With a floating caliper, the mounting bracket captures the pads. As a result, the caliper doesn't have to be as beefy.

Types Of Discs
Although disc brake rotors come in a wide variety of sizes, they can be broken down into just two categories: solid and vented. Solid rotors are just that, a simple flat rotor. Simple and inexpensive. The disadvantage to solid rotors is that they do not dissipate heat well. While solid rotors are adequate for lightweight cars, particularly on the rear, a better disc brake rotor option for trucks is the vented style. This design separates the two friction surfaces with air passages to aid in cooling.

Hydraulics
Another important factor in the way brakes function is the amount of pressure available to apply to the friction surfaces against the rotating surfaces. If you've ever stomped on a brake pedal in a panic, you grasp the basic concept; more pressure means a shorter stop. Modern hydraulic brake systems are based on the principles first put forth by a 17th century mathematician, Blaise Pascal. He found that a liquid does not compress and that pressure applied to a liquid in a closed system is transmitted equally to every other part of the system. For our purposes that means if 100 pounds of pressure is applied to a 1-square-inch-piston in the master cylinder that results in 100 psi in the hydraulic system. The fluid passes through the brake lines to a wheel cylinder with a 1-square-inch-piston and it will push with 100 pounds of force.

Now take the same scenario and add three more wheel cylinders and pressure at all the wheel cylinders is the same. Now this is where things get interesting. In this scenario, 100 pounds of pressure is applied to the same master cylinder with a 1-square-inch-piston. The system pressure is still 100 psi; however, now the piston in the wheel cylinder is increased to 3 square-inches. Because the pressure in the system is 100 psi, and the wheel cylinder has 3-square-inches of surface area, the result is the piston pushes with 300 pounds of force. That simply means that increasing the surface area of the pistons at the wheels (disc brake calipers or drum brake wheel cylinders) increases the force applied to the friction surfaces, and all things considered, the more pressure applied to the friction surfaces the more stopping power.