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Brake pads
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Brake pads are an important part of braking systems for all types of vehicles that are equipped with disc brakes. Brake pads are steel backing plates with friction material bound to the surface facing the brake disk.
Function
Brake pads convert the kinetic energy of the car to thermal energy by friction. Two brake pads are contained in the caliper with their friction surfaces facing the rotor. When the brakes are hydraulically applied, the caliper clamps or squeezes the two pads together into the spinning rotor to slow/stop the vehicle.
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Encyclopedia
Brake pads are an important part of braking systems for all types of vehicles that are equipped with disc brakes. Brake pads are steel backing plates with friction material bound to the surface facing the brake disk.
Function
Brake pads convert the kinetic energy of the car to thermal energy by friction. Two brake pads are contained in the caliper with their friction surfaces facing the rotor. When the brakes are hydraulically applied, the caliper clamps or squeezes the two pads together into the spinning rotor to slow/stop the vehicle. When a brake pad is heated up by coming into contact with either a drum or rotor, it starts to transfer small amounts of friction material to the disc or pad (that is the reason a brake disk has a dull grey). The brake rotor and disk (both now with friction material on), will then "stick" to each other to provide stopping power. The friction of the pad against the disk is however responsible for the majority of stopping power.
In disc brake applications, there are usually two brake pads per disc rotor, held in place and actuated by a caliper affixed to a wheel hub or suspension upright. Although almost all road-going vehicles have only two brake pads per caliper, racing calipers utilize up to six pads, with varying frictional properties in a staggered pattern for optimum performance.
Depending on the properties of the material, disc wear rates may vary. The brake pads must usually be replaced regularly (depending on pad material), and most are equipped with a method of alerting the driver when this needs to take place. Some have a thin piece of soft metal that causes the brakes to squeal when the pads are too thin, while others have a soft metal tab embedded in the pad material that closes an electric circuit and lights a warning light when the brake pad gets thin. More expensive cars may use an electronic sensor.
Technology
Advantages of brake pads
These brakes offer better stopping performance than comparable drum brakes, including resistance to "brake fade" caused by the overheating of brake components, and are able to recover quickly from immersion (wet brakes are less effective). Unlike a drum brake, the disc brake has no self-servo effect and the braking force is always proportional to the pressure placed on the braking pedal or lever.
Laser shaping
Ordinary brake pads inherit vibration characteristics since the shape of the pad and contact of the caliper piston causes vibration that distorts the contact or the transfer of force to the rotor upon contact. The new laser cutting technology of the pad decreases the contact area and focuses on more force being distributed over a smaller amount of an area for more positive contact of the pad and rotor creating more efficient quality stopping.
Laser burnishing process
A precisely controlled laser beam is used to heat and condition the pad surface, eliminating the need for a traditional break-in period on the vehicle following installation.
IMI-sound insulator
Spreads out and absorbs heat and energy over a greater surface area for longer brake pad life and quiet performance.
Types
There are numerous types of brake pads, depending on the intended use of the vehicle, from very soft and aggressive (such as racing applications) and harder, more durable and less aggressive compounds. Most vehicle manufacturers recommend a specific compound of brake pad for their vehicle, but compounds can be changed (by either buying a different make of pad or upgrading to a performance pad in a manufacturer's range) according to personal tastes and driving styles. Care must always be taken when fitting non standard brake pads, as operating temperature ranges may vary, such as performance pads not braking efficiently when cold or standard pads fading under hard driving. In cars that suffer from excessive brake fade, the problem can be minimized, by installing better quality and more aggressive brake pads.
Materials
Brake pad materials range from asbestos to organic or semi-metallic formulations. Each of these materials has proven to have advantages and disadvantages regarding environmental friendliness, wear, noise and stopping capability.
Semi-metallic pads to provide strength and conduct heat away from rotors also generate noise and are abrasive enough to increase rotor wear.
Ceramic compounds and copper fibers in place of the semi-metallic pad's steel fibers provide high brake temperatures with less heat fade, generate less dust and wear on both the pads and rotors. They also provide much quieter braking because the ceramic compound helps dampen noise by generating a frequency beyond the human hearing range and utilize less metal (approximately 15% metal content by weight). Ceramic brake pads therefore outlast other premium pad materials by a significant margin - with no sacrifice in noise control, pad life or braking performance.
Asbestos was widely used in pads for its heat resistance, but due to health risks it has now been replaced by a mix of alternative fibers such as mineral fibers, cellulose, aramid, PAN, chopped glass, along with steel and copper fibers. Depending on the properties of the material, disc wear rates may vary. The properties that determine material wear involve trade-offs between performance and longevity. Newer pads can be made of exotic materials like ceramics, Kevlar and other plastics.
Vehicles have different braking requirements; friction materials offer the application-specific formulas and designs. Brake pads with a higher coefficient of friction provide good braking with less brake pedal pressure requirement tend to lose efficiency at higher temperatures, which means that the stopping distance will be increased. Brake pads with a smaller and constant coefficient of friction don’t lose the efficiency at higher temperatures and are stable but still require higher brake pedal pressure.
Precautions
Care to avoid inhalation of brake dust produced during operation should be practiced no matter what materials are employed. An approved filter mask should be worn when working on brakes and never blow out the brakes with compressed air. Usage of petroleum-based solvents to clean brakes is a fire danger. Use of brake parts cleaner is recommended. Extensive damage may occur if the pads are not replaced when necessary. Brake pads must be replaced in pairs, that is either a complete axle front or rear changed at the same time.
Bedding-in pads
Proper bed-in procedures have to be followed in order to extend the life of brake pads and maximize performance. This process will lay down a thin layer of transfer film on to the rotor surface. Following the bed-in procedures provided by the manufacturer will assure a smooth, even layer of transfer film on the rotor and will minimize brake judder.
- Loosen the wheel lug nuts, raise the front of the vehicle and support it securely on jack stands placed under the frame rails or subframe.
- Block the wheel at the opposite end of the vehicle to prevent it from rolling. Remove the wheel lug nuts completely and then the wheel.
The disc brake calipers, which contain the pads, are visible with the wheels removed, There is an out and inner pad in each caliper where the disk is sitting in between. All components should be inspected including the pads, rotors and brake calipers for anything that is out of the ordinary. Most calipers have a window or an opening on top of the brake caliper to inspect the brake pad thickness. Generally the pad has to be replaced if the material has worn to 3/16-inch or less.
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