Brake Definitions

From Nissan 350Z & 370Z Wiki

1 Brake Fading
2 Calipers
3 Disc Brake
4 Drum Brake
5 Fluid
6 Lines
7 Master Cylinder
8 Pads
9 Parking Brake
10 Rotors

Brake Fading

Brake fading, or brake fade, is a condition in which the brakes loose some of their friction potential, usually due to excessive heat build up on the braking surface or friction material. It most commonly occurs during repeated hard braking, or braking while under a very heavy load (lots of extra weight, or downhill)

The most common type of brake fade is due to boiling of the brake fluid. This causes the hydraulic pressure on the calipers or servo to lessen, there by reducing overal brake pedal feel and/or stopping distance.

Different types of fluids have different boiling points, depending upon your application it may be well worth spending extra money for a brake fluid with a higher boiling point, provided it is within the correct DOT classification.

The second type of brake fade is pad fade. The pad basically melts due to the extreme heat. This can be compensated for by having a brake pad that suits the use of the car. Race pads for track days, and street pads for the street. Having a track pad all the time will not work because on the street it will most likely not reach its optium operating temperature.

Some things that can be done to prevent brake fade are proper dissipation of heat, and in more extreme conditions air ducting to cool the friction material/surface.

Calipers

The brake caliper is the assembly which houses the brake pads and pistons. The pistons are usually made of aluminum or chrome plated iron. There are two types of calipers: floating or fixed.

A fixed caliper does not move relative to the disc. It uses one or more pairs of pistons to clamp from each side of the disc, and is more complex and expensive than a floating caliper.

A floating caliper (also called a "sliding caliper") moves with respect to the disc; a piston(s) on one side of the disc pushes the inner brake pad till it makes contact with the braking surface, then pulls the caliper body with the outer brake pad so pressure is applied to both sides of the disc.

Floating caliper designs are subject to failure due to sticking. This can occur due to dirt or corrosion if the vehicle is not operated. This can cause the pad attached to the caliper to rub on the disc when the brake is released. This can reduce fuel mileage and cause excessive wear on the affected pad.

Disc Brake

A disc brake stops movement by forcing a friction material (brake pad) against a rotating metallic or synthetic disc. Disc brakes come in many different sizes, and include many different features.

Drum Brake

A drum brake stops movement by forcing a friction material (brake shoe) against a rotatating metallic drum. Drum brakes come in many different sizes are are widely accepted as inferior to disc brakes in automobile applications.

Fluid

Brake fluid is a type of hydraulic fluid used in brake applications in automobiles and light trucks. It is used to transfer force under pressure from where it is created through hydraulic lines to the braking mechanism near the wheels. It works because liquids cannot be compressed. Braking applications produce a lot of heat so brake fluid must have a high boiling point to remain effective and must also not freeze under normal temperatures. These requirements eliminate most water-based solutions.

Brake fluid can come in a number of forms, standardized under the DOT (Department of Transportation) standard. DOT 2 is essentially castor oil; DOT 3, DOT 4, and DOT 5.1 are composed of various glycol esters and ethers; and DOT 5 is silicone-based. Most cars produced in the US use DOT 3.

Glycol based fluids are 2 times less compressible than silicone type fluids, even when heated. Less compressibility of brake fluid will increase pedal feel. Glycols are hygroscopic and will absorb water from the atmosphere, reducing the boiling point of the fluid and degrading hydraulic efficiency. Changing fluid on a regular basis will greatly increase the performance of the brake system, but this is often not a concern in passenger cars. On the other hand, changing fluid at least every several years will preserve the life of brake system components (by removing accumulated water and other contaminants) and increase the overall reliability of the brake system.

Polyethylene glycol and other brake fluid ingredients may be corrosive to paint and finished surfaces such as chrome and thus care should be taken when working with the fluid.

Lines

Brake Lines are metallic or rubber and metallic hoses that allow brake fluid to flow from the master cylinder to the proportioning valve then to either brake calipers, wheel cylinders, or a combination of both. Brake lines are normally replaced and not repaired, as then endure high pressure. A popular upgrade is installing stainless steel lines in place of the stock rubber lines. Although this will not improve braking distance, it can improve brake pedal feel, thereby allowing the driver to modulate the pedal accordingly under braking.

Master Cylinder

A master cylinder is a pump and reservoir mechanism, either all metal or a combination of metal and plastic, which creates pressure, when the plunger is depressed. The upper portion of the unit is the reservoir, which contains brake fluid, it can be one container unit or separated into two chambers.

A two chamber unit will separate the front brakes from the rear. The lower unit, the actual pump, has a plunger that enters the cabin of the car which the brake pedal is attached to with a rod mechanism. Typically, there are two lines that are connected to the master cylinder that joins it to a proportioning valve. The one line controls the front and the other controls the rear brakes.

The master cylinder creates high pressure to the fluid and when internal damage occurs, the pedal will sink to the floor board and proved little to no breaks. It is vital that a master cylinder is bled before installing and the whole system is bled once installed, to remove any air that might have been trapped.

Bench bleeding is a process in which plastic clear tubing is routed from the break line ports of the master cylinder to the reservoir, filled with brake fluid, and the plunger is depressed until all air is out and only fluid is seen passing through, or no bubbles are formed at the reservoir. When re-installing the master cylinder, air must be bled out of the rest of the lines starting from the furthest cylinder (or caliper) to the nearest. There are several ways of bleeding the lines, one is vacuuming the fluid from each bleeder valve, another is pumping the system with the brake pedal and holding it while the valve is opened then closed before pumping it again, until a solid flow of brake fluid is released. Another is using a container at the valve with fluid and a hose from the valve to the container, and pumping the pedal several times until there are no bubbles forming in the container.

Pads

A brake pad is a material that lies between the piston and the rotor's surface inside the brake caliper. Powered by hydraulic pressure, the pads force themselves against the rotors surface, providing the friction needed to stop the vehicle.

When purchasing aftermarket brake pads it is important to note the operational temperature as some will take considerably longer to effectively stop the vehicle when cold.

Parking Brake

Most vehicles include a mechanical parking brake system (also called an "emergency brake") which operates on the rear wheels. These systems are very effective with drum brakes, since these tend to lock. The adoption of rear-wheel disc brakes caused concern that a disc-based parking brake would not effectively hold a vehicle on an incline. Though some early vehicles (like the Toyota 2000GT) did use the disc for the parking brake, others used a tiny drum brake embedded inside the rear disc.

Today, most cars use the disc for parking, though some still rely on separate drums. The advent of electric parking brakes will change the rear caliper configuration substantially.

Rotors

A disc-shaped component that revolves with hub and wheel. The brake pads are forced against the rotor to provide a friction surface for the brake system, so as to slow or stop a vehicle.

Brakes