Dictionary of Automotive Terms: A

AAA: American Automobile Association.

ABDC: After Bottom Dead Center.

ABSOLUTE ZERO: A state in which no heat is present. Believed to be -459.7°F or -273.16°C.

AC: Alternating current.

ACCELERATOR: Floor pedal used to control, through linkage, throttle valve in carburetor.

ACCELERATOR PUMP: Small pump, located in carburetor, that sprays additional gasoline into air stream during acceleration.

ACCUMULATOR (Air Conditioning): Receiver-dehydrator combination.

ACCUMULATOR PISTON (Automatic Transmission): Unit designed to assist the servo to apply brake bank quickly, yet smoothly.

ACETYLENE: Gas commonly used in welding or cutting operations.

ACKERMAN PRINCIPLE: Bending outer ends of steering arms slightly inward so that when car is making a turn, inside wheel will turn more sharply than outer wheel. This principle produces toe-out on turns.

ADDITIVE: Solution, powder, etc., added to gasoline, oil, grease, etc., in an endeavor to improve characteristics of original product.

ADVANCE (Ignition timing): To set ignition timing so a spark occurs earlier or more degrees before TDC.

AEA: Automotive Electric Association.

AERA: Automotive Engine Rebuilders Association.

AFBMA: Antifriction Bearing Manufacturers Association.

AHRA: American Hot Rod Association.

AIR: Air Injection Reactor system of reducing objectionable exhaust emissions.

AIR BLEED: An orifice or small passageway designed to allow a specific amount of air to enter a moving column of liquid (such as fuel).

AIR CLEANER: Device used to remove dust, abrasive, etc., from air being drawn into an engine, compressor, power brake, etc.

AIR CONDITIONING: Controlling the temperature, movement, cleanliness, and humidity of air.

AIR COOLED: An object cooled by passing a stream of air over its surface.

AIR DAM: A device placed beneath front bumper to reduce amount of air turbulence and drag under car.

AIR FILTER: A device through which air is drawn to remove dust, dirt, etc.

AIR FOIL: Device, similar to a stubby wing, mounted onto a racing car or dragster to provide high speed stability. The air foil is mounted in a horizontal position.

AIR-FUEL RATIO: Ratio (by weight or by volume) between air and gasoline that makes up engine fuel mixture.

AIR GAP (Regulator): Distance between contact armature and iron core that when magnetized, draws armature down.

AIR GAP (Spark Plugs): Distance between center and side electrodes.

AIR HORN (Carburetor): Top portion of air passageway through carburetor.

AIR HORN (Accessory): Warning horn operated by compressed air.

AIR INJECTION REACTION: An emission control system used to lower levels of car bon monoxide and hydrocarbon emissions. Accomplished by injecting a stream of air into exhaust stream near exhaust valve.

AIR POLLUTION: Contamination of earth’s atmosphere by various natural and manufactured pollutants such as smoke, gases, dust, etc.

AIR SPRING: Container and plunger separated by air under pressure. When container and plunger attempt to squeeze together, air compresses and produces a spring effect. Air spring has been used on some suspension systems.

ALIGN: To bring various parts of unit into correct positions in respect to each other or to a predetermined location.

ALLOY: Mixture of two or more materials.

ALNICO MAGNET: Magnet using (Al) aluminum, (Ni) nickel, and (Co) cobalt in its construction.

ALPHA NUMERIC (Tire): Tire size designation using letters to indicate load carrying capacity. Example: GR 78-15. The letter G = load/size relationship. R = radial construction. 78 = height to width ratio. 15 = rim diameter in inches.

ALTERNATOR: Device similar to generator but which produces AC current. The AC must be rectified before reaching the car’s electrical system.

ALTERNATING CURRENT (AC): Electric current that first flows one way in circuit and then other. Type used in homes.

AMA: Automobile Manufacturers Association.

AMBIENT TEMPERATURE: Temperature of air surrounding an object.

AMC: American Motors Corporation.

AMMETER: Instrument used to measure rate of current flow in amperes.

AMPERE: Unit of measurement used in ex pressing rate of current flow in a circuit.

AMPERE HOUR CAPACITY: Measurement of storage battery ability to deliver specified current over specified length of time.

ANEROID: A device, such as a barometer bellows, that neither contains nor uses a liquid.

ANEROID BAROMETER: A device to measure atmospheric pressure. It utilizes an aneroid capsule (bellows) that expands and contracts with differences in pressure.

ANGLE OF APPROACH: The steepest angle that a vehicle can drive up on from a level surface without dragging the front end of vehicle.

ANGLE OF DEPARTURE: The steepest angle that a vehicle can descend and drive off onto a level surface without dragging rear of vehicle.

ANNEAL: To remove hardness from metal. Heat steel to a red color, then allow it to cool slowly. Unlike steel, copper is annealed by heating, and then plunging it immediately into cold water.

ANODE: In an electrical circuit — the positive pole.

ANTIBACKFIRE VALVE: Valve used in air injection reaction (exhaust emission control) system to prevent backfiring during period immediately following sudden deceleration.

ANTIFREEZE: Chemical added to cooling system to prevent coolant from freezing in cold weather.

ANTIFRICTION BEARING: Bearing containing rollers or balls plus an inner and outer race. Bearing is designed to roll, thus minimizing friction.

ANTIKNOCK (Fuel): Indicates various substances, such as tetraethyl lead, that can be added to gasoline to improve its resistance to knocking (spark knock, pre-ignition, or detonation).

ANTIPERCOLATOR: Device for venting vapors from main discharge tube, or well, of a carburetor.

API: American Petroleum Institute.

APRA: Automotive Parts Rebuilders Association.

APPRENTICE PROGRAM: Educational program designed to teach a trade through on-the-job training and study.

ARC OR ELECTRIC WELDING: Welding by using electric current to melt both metal to be welded and welding rod or electrode that's being added.

ARCING: Electricity leaping the gap between two electrodes.

ARMATURE (Relay, regulator, horn, etc.): The movable part of the unit.

ARMATURE (Starter or generator): The portion that revolves between the pole shoes, made up of wire windings on an iron core.

ASBESTOS: Heat resistant and non-burning fibrous mineral widely used for brake shoes, clutch linings, etc. Do not inhale asbestos fibers or dust. Believed to cause cancer.

ASLE: American Society of Lubrication Engineers.

ASME: American Society of Mechanical Engineers.

ASSE: American Society of Safety Engineers.

ASPECT RATIO (Tire): Ratio between height and width of a tire.

ASTM: American Society of Testing Materials.

ASYMMETRIC TIRE TREAD: Tire tread with a non-symmetrical (uneven) pattern. Designed to reduce tire vibration and noise.

ATA: American Trucking Association.

ATDC: After Top Dead Center.

ATMOSPHERE: Layer of gases (referred to as air) surrounding earth.

ATMOSPHERIC PRESSURE: Pressure exerted by atmosphere on all things exposed to it. Around 14.7 pounds per square inch or 101 kPa at sea level.

ATOM: Tiny particle of matter made up of electrons, protons, and neutrons. Atoms or combinations of atoms make up molecules. The electrons orbit around the center or nucleus made up of the protons and neutrons.

ATOMIZE: To break a liquid into tiny droplets.

AUTOMATIC CHOKE: A carburetor choke device that automatically positions itself in accordance with carburetor needs.

AUTOMATIC LEVELING CONTROL: Pressure system which maintains proper body height with changes in load.

AUTOMATIC TRANSMISSION: A transmission that shifts itself. Shift range and points are determined by road speed, quadrant position, engine loading, altitude, etc.

AWL (Tire): Sharp pointed steel tool used to probe cuts, nail holes, etc., in tires.

AXIAL: Direction parallel to shaft or bearing hole.

AXLE (Full-floating): Axle used to drive rear wheels. It does not hold them on nor sup port them.

AXLE (Semi or one-quarter floating): Axle used to drive wheels, hold them on, and sup port them.

AXLE (Three-quarter floating): Axle used to drive rear wheels as well as hold them on. It does not support them.

AXLE END GEARS: Two gears, one per axle, that are splined to the inner ends of drive axles. They mesh with and are driven by “spider” gears.

AXLE HOUSING: Enclosure for axles and differential. It is partially filled with differential fluid (oil).

AXLE RATIO: Relationship or ratio between the number of times the propeller shaft must revolve to turn the axle drive shafts one turn.