Brake Industry Definitions

• AK master: A dynamometer test developed by automotive engineers in Europe. This test is for general performance of friction materials.

• AK noise: A dynamometer test developed by automotive engineers in Europe. This test is for noise performance of friction materials.

• AMECA: Automotive Manufacturers Equipment Compliance Agency, Inc. This agency certifies the friction level of friction material. The friction level is the last two characters of the edge code; for example, N501H FF.

• AMS: Vehicle tests developed by the German automotive magazine Auto Motor und Sport. These tests are intended for high performance sports cars.

• Back plate: Steel plate to which friction material is molded or riveted to produce a disc brake pad.

• Bonded lining: Brake lining (friction material) attached to the brake shoe with adhesive.

• Brake fade: A reduction or loss in braking force due to loss of friction between the disc pad and the rotor. Fade is caused by heat build-up through repeated or prolonged brake application.

• Brake lining: Another term for friction material.

• Brake shoe: Correctly, the shoe is the metal component (rim and web assembly) used to push the friction material against the drum in a drum brake system, but the term is now used to refer to the whole shoe and lining assembly.

• Caliper: A type of clamp that grips a disc rotor to create friction and thereby generate the braking action.

• Coefficient of friction: A measurement of the amount of friction developed between two objects or surfaces in physical contact when one of the objects is drawn across the other. This coefficient of friction is dependent upon both surfaces in contact. The coefficient is large if the surfaces are rough and small if they are smooth. The label given to coefficient of friction is m (mu); its value ranges from 0 to 1.0.

• Creep groan: A noise that occurs at very low vehicle speed (under 2 mph) when applying or holding the brake ON. Creep groan is caused by brake lining "stick-slip". It usually experienced on vehicles with automatic transmissions.

• DIH: Drum In Hat, a type of parking brake system used with vehicles that have rear disc brakes. DIH utilizes two drum brake linings inside the hat area of the brake rotor.

• Disc brake: A type of brake using a rotor as a surface on which a caliper generates frictional forces.

• Disc brake pad: The component in a disc brake system that is fitted with friction material and clamped against the brake disc (rotor) to cause friction.

• Drum brake: A type of brake in which a circular drum rotates around a set of brake shoes which are fixed to the hub and act on the drum by expanding.

• DST: Detroit Suburban Traffic vehicle test. This test is used to evaluate DTV generation by friction materials.

• DTV: Disc Thickness Variation, the variation in thickness between two points on the friction surface of a rotor. It is usually caused by poor alignment of the rotor/caliper or the rubbing of the friction material against the rotor when the brakes are off.

• Dynamic groan: Noise that occurs at high speeds, usually caused by an uneven transfer layer (stick-slip).

• Dynamometer: A machine that measures the input or output of power generating, power transmitting, or power absorbing machinery. The power is typically measured in terms of speed and torque.
  As it relates to automotive brakes, a dynamometer is a machine which consists of a motor driving a specified inertia load (to simulate the energy of the vehicle being tested) and a hydraulic system that can accurately control the brake pressure and/or torque of the brake being tested. Dynamometers are often referred to as dynos in North America and are used to test for performance, wear, noise, rotor aggressiveness, DTV, and other characteristics.

• Flash mold: A molding process used for friction material. This process utilizes constant volume for each part; the excess material is "flashed" outside the mold cavity.

• FMVSS 135: Federal Motor Vehicle Safety Standards--government standards for dynamometer and vehicle testing required for vehicle manufacturers in the United States.

• Foundation brakes: Those parts of the brake system responsible for the generation of wheel braking torque and thermal energy storage and dissipation.

• Friction: Resistance to movement between any two objects when placed in contact with each other. Friction causes wear and heat.

• Friction material: Materials used to generate frictional forces in disc or drum brakes.

• High-speed judder: Vibration during high speed braking not related to DTV. It is caused by hot spots or foreign material on the rotor.

• Howl: Noise generated in the range of 500 to 1,000 Hz and caused by stick-slip.

• JASO - Japanese Automobile Standards Organization.

• Judder: Vibration during braking at low speeds. Judder is caused by DTV. See also high-speed judder.

• LACT: Los Angeles City Traffic vehicle test, used to evaluate life (wear) and noise generation of friction materials.

• Lining: Another term for friction material.

• Low steel: Friction material composed of 10% to 30% steel fiber.

• NAO: Non Asbestos Organic friction material composed of less than 10% steel fiber.

• Positive mold: A molding process used for friction material. This process utilizes constant pressure and therefore produces no "flash" of excess material.

• Rotor scoring: Grooves on the friction surface of the brake rotor, usually caused by the friction material.

• SAE: Society of Automotive Engineers.

• Service brakes: Another name for foundation brakes.

• Semi-metallic: Friction material composed of 30% to 60% steel fiber.

• Squeal (low frequency): Noise generated in the range of 800 to 5,000 Hz and caused by the positive mechanical feedback excitations from the brake linings.

• Squeal (high frequency): Noise generated in the range of 5,000 to 18,000 Hz and caused by the positive mechanical feedback excitations from the brake linings.

• Stick-slip: A phenomenon caused by a non-linear change in the coefficient of friction. When the m (coefficient of friction) increases, the two surfaces will stick. As the rotational force increases or the m decreases, a sudden release or slip will occur between the two surfaces.

• Transfer layer: The transfer of friction material to the brake drum or rotor. The thickness increases with temperature and the number of braking cycles; thickness is also directly related to the amount of stick-slip.