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Disc brake pads have built-in wear indicators that will make a high pitched squealing or scraping noise when they are worn to the replacement point. When you hear this noise replace the pads immediately or expensive damage to the discs can result.
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.
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 provide strength and conduct heat away from rotors but 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 use less metal (approximately 15% metal content by weight). Ceramic brake pads typically are suited for light-duty applications and not severe duty applications, medium duty trucks, etc.
There are environmental factors that govern the selection of brake pad materials. For example, recent legislation in some states will limit the amount of copper that is allowed to be used in friction materials, to be eventually phased out to trace amounts. Other materials like antimony compounds will be monitored as well.
Asbestos was widely used in pads for its heat resistance, but due to health risks has been replaced with alternative materials, such as mineral fibers, cellulose, aramid, PAN, chopped glass, steel, and copper fibers. Depending on material properties, disc wear rates vary. The properties that determine material wear involve trade-offs between performance and longevity. Newer pads can be made of exotic materials like ceramics, aramid fibres, and other plastics. Vehicles have different braking requirements. Friction materials offer application-specific formulas and designs. Brake pads with a higher coefficient of friction provide good braking with less brake pedal pressure requirement, but tend to lose efficiency at higher temperatures, increasing stopping distance. Brake pads with a smaller and constant coefficient of friction don’t lose efficiency at higher temperatures and are stable, but require higher brake pedal pressure.
The appropriate disc pads and rotors or drums and shoes for your vehicle depends on the vehicle’s requirements, your typical driving circumstances and your personal preferences. Consult with your mechanic to determine the best solution for your vehicles.
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