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Glossary of Technical Terms

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Ab     Ac     Ad     Ae     Af     Ai     Al     Am     An     Ar     As     Au     Aw     Ax

A-2 tire  A term used for tire sizes 16.00 and larger in nominal cross section. Also called earthmover or off-the-road tire

A-Arm See control arm.

A-arm suspension  See double wishbone.

Abampere  A unit of electric current in the CGS electromagnetic system of units. One abampere equals 10A.

ABPV  Acronym for "air bypass valve" or anti-backfire valve

ABS Acronym for "anti-lock brakes.

A system, usually electronically controlled, that senses incipient wheel lockup during braking and relieves hydraulic pressure at wheels that are about to skid.

ABS override button A button or switch which disengages the automatic anti-lock braking system so that the driver can operate the brakes himself.

ABV Acronym for "air bypass valve" or anti-backfire valve

A/C   An abbreviation for air conditioning or air conditioner.


[1] Acronym for "alternating current." 
Alternating current or altitude compensator; also Ac, Actinium An element with the atomic number of 89

[2] Acronym for "air conditioning" or "air conditioner."

AC/TVS  Air cleaner/thermal vacuum switch

Accelerate  To increase the speed of a vehicle.

Accelerator   In automobiles, this is the "gas pedal" which is attached by linkage to the throttle in the carburetor or to the fuel injection system. It regulates the amount of fuel which is sent to the engine.
On motorcycles, the accelerator is located on the right-hand twist grip or an actuating lever.

Accelerator Pedal

The accelerator, gas pedal, or throttle pedal.



Accelerator Pump  A small cylinder and piston usually located inside the carburetor that sprays an extra amount of fuel into the engine during acceleration. It improves acceleration by giving more boost and reducing a momentary lag in power. It is actuated by depressing the pedal.

Accord A model of automobile manufactured by Honda

Ackermann Steering

[1] A double-pivoting steering system where the outer ends of the steering arms are bent slightly inward so that when the vehicle is making a turn, the inside wheel will turn more sharply than the outer wheel. This is done to compensate for the greater distance the outside wheel must travel. Notice 20 degrees on left wheel and 30 degrees on right wheel

[2] Arrangement whereby a line extended from the track-arms, when the wheels are set straight ahead, should meet on the chassis centerline at 2/3 of the wheelbase from the front, allowing the inner stub-axle to move through a greater angle than the outer.

Ackermann angle  The toe-out or toe-in of a vehicle with Ackermann steering when the wheels are positioned straight ahead.

Ackermann axle In a vehicle with Ackermann steering (at the front of the vehicle), it is a non-rotating axle that is steerable and has two pivot points (one on each end of the axle) with vertical kingpins.

Acura A vehicle brand from the Honda manufacturers

Adjusting Screw  A small screw usually found on carburetors, brakes, or headlights which change the way something operates, such as increasing or decreasing the amount of fuel entering the engine; or changing the idle speed; or tightening up the brakes; or changing the setting on rocker arms; or the level of the headlights.

Explore The Carburetor

Aerodynamics The study of the flow of air as it passes over and around a moving object as well as the forces which the air makes on the object. An airplane, for instance, needs positive lift to get it airborne and negative lift to help it land. Thus the shape of a land vehicle (car, bicycle, etc.) either promotes positive or negative lift. Race cars may use spoilers and wings (air foils) to control lift. In vehicle design, the airflow is monitored in a wind tunnel. As well, aerodynamics also studies the most efficient shapes for increased speed and fuel economy.

AF Ratio
A/F Ratio See air-fuel ratio 

Aftermarket  All products and services used in the repair and maintenance of vehicles after the vehicle has been sold.

Aftermarket part  Goods not for use as original equipment in the production of light-duty vehicles or heavy-duty vehicles, i.e., products and services used in the repair and maintenance of these vehicles

Air bag  An inflatable bag hidden in the steering wheel (driver's side) or the dash or glove box (passenger side). In a head-on collision, the bags inflate, preventing the driver and front passenger from being thrown forward into the steering wheel or windshield.

Air Brake:

[1] A system of braking which is usually found on large truck in which compressed air pushes against a brake piston or diaphragm in order to apply the brakes to stop or slow the vehicle.

[2] A mechanical brake operated by air-pressure acting on a piston 

Air Bypass Valve
Air By-pass Valve

(ABPV or ABV) a backfire-suppressor valve used in air injection systems. During high engine vacuum conditions such as deceleration, it vents pressurized air from the air pump to the atmosphere in order to prevent backfiring. At other times, it sends air to the exhaust manifold. On vehicles with a three-way catalyst, it sends air to the oxidation catalyst only when the engine warms up.

Also called an anti-backfire valve, diverter valve, or gulp valve.

Air cleaner  A metal or plastic housing, containing a filter element, whichremoves dust and dirt from the air being drawn into the engine.



Air Conditioner  (A/C) or (Air)

[1] A device used to control temperature, humidity, cleanliness, and movement and sometimes the air purity, in an enclosed space

[2] A system of devices which causes a reduction or control of the temperature and humidity within the cab of a vehicle. It was first offered on the 1941 Packard. Two types are used in vehicles: Receiver-dryer type and accumulator type.

Air Filter or  Air filter ELEMENT

 The actual filter in an air cleaner system, usually manufactured from pleated paper and requiring renewal at regular intervals.




Airflow Sensor  A device in an electronically controlled fuel injection system which detects the amount of air entering the combustion chambers. Continuous injection systems use an airflow sensor plate to measure airflow volume; electronic systems use a vane or flap-type airflow sensor.

 The Airflow Sensor or Mass Airflow Sensor (MAF) used to measure amount of air entering the engine. Usually it's located in the intake after the air filter, before the throttle. Based on MAF sensor readings, the engine computer (ECM) calculates proper amount of injected fuel.

Air Fuel (air-fuel, air/fuel)

See air-fuel ratio

Air Fuel Mixture (Air-Fuel Mixture) See rich air-fuel mixture  and  lean air-fuel mixture

Air Fuel Ratio (air-fuel ratio, A/F ratio)  The mass of air supplied to the engine divided by the mass of fuel supplied in the same period of time. The stoichiometric, or chemically correct, air-fuel ratio is the exact ratio necessary to burn all the carbon and hydrogen in the fuel to carbon dioxide and water with no oxygen remaining. The fuel-air ratio is the reciprocal of the air-fuel ratio.

Also see  

lean air-fuel mixture
rich air-fuel mixture 

Air Intake

The opening through which air enters a component such as the carburetor (Vent in a carburetor through which air is sucked to mix with the gasoline vapor from the jet) , fuel injection system, radiator, heating system, or ventilation system. See cold air intake.

Air Shock Absorber A shock absorber or damper which has a rubber bladder filled with compressed air. As the air pressure increases the vehicle is raised. The system is used in automatic leveling suspensions.

Air Suspension  A suspension system using air rather than metal springs to support the vehicle and control ride motions.

 Air springing results in a smoother ride, because the natural frequency of vibration of an air spring does not vary with loading as it does with metal springs. Air springs can be made very soft for the lightly loaded condition and the pressure automatically increased to match any increase in load, thus maintaining a constant sprint vibration period any load.

Alignment  When referring to wheel alignment, it is the proper adjustment of a vehicle's front or rear suspension for camber, toe-in, toe-out, kingpin inclination or steering axis inclination, and turning radius or toe-out on turns, caster, and ride height. Four-wheel alignment is necessary for front-wheel drive vehicles.

Allen key  A hexagonal wrench which fits into a recessed hexagonal hole.

Allen Wrench  A rod with six sides and often L-shaped. Used to remove certain screws and fastenings, especially set screws. Sometimes called "hex wrenches" or "Allen key."

Alligator clip  A spring-loaded metal clip with meshing teeth. Used to make temporary electrical connections. As you squeeze the two "legs"

of the clip, the other two jaws (usually serrated) open. Used to make temporary electrical connections. Larger ones are used at the ends of jumper cables.

Alloy Wheel  A generic term used to describe any non-steel road wheel. The usual alloys are either aluminum or magnesium; the latter material led to the common usage of the term "mag wheel," often referring to any non-steel wheel.

All Terrain Tire A tire which has a number of lugs or knobs used to propel the vehicle over rough surfaces.

All Terrain Vehicle A vehicle used in rough surface conditions. Also called off-road vehicle

All-Weather Tire A tire that can be used on roads that is bare or covered with rain, snow, or ice.

All-Wheel Drive (AWD) A variation of four-wheel drive (4WD) designed to improve on-road traction in unfavorable road conditions or for ultra high performance driving. All-Wheel Drive ( WD) reduces wheel slippage and provides greater driver control over the vehicle. AWD usually does not require the driver to actively engage the system and does not have a low range. AWD automatically splits engine torque between the front and rear wheels as needed. All-Wheel Drive is generally an on-road system and is not designed for off-road use.

Alternator  The chief source of power of the electrical system is the

alternating-current generator, or alternator. Its shaft is driven by the same belt that spins the fan and it keeps the engine running and also recharges the battery when the engine is running. It converts mechanical energy into alternating-current electricity, which is then channeled through diodes that alter it to direct current for the electrical system and for recharging the battery.


 If the alternator fails, the engine will continue to run using the battery power, but the car will eventually stop as soon as the battery will be completely discharged. When the alternator fails, there is a warning light on the instrument panel that comes on with the engine running. Usually it's something like or "charge" warning light. If you see that sign on your instrument panel while driving, have your vehicle inspected before it dies on you.

Ammeter  The device is used to determine whether the electrical system is charging, discharging, or staying "level". The gauge should dip when the engine is started, then go up as the alternator re- charges the battery. After a few minutes, it should go to its middle position.

Ampere (amp)  A unit of measurement for the flow of electric current. One amp is the amount of current produced by one volt acting through a resistance of one ohm.

Anaerobic sealer  A substance used to prevent bolts and screws from loosening. Anaerobic means that it does not require oxygen for activation. The Loctite brand is widely used.

Anode  In an electrical circuit it is the positive pole. It is that part of an electrical circuit to which electrons are flowing.

Antenna  A device which pulls in radio reception. A power antenna automatically rises when the radio is turned on and lowers when it is shut off. Some cars had the antenna wires imbedded in the windshield.

Anti-Backfire Valve  Valve used in air injection reaction (exhaust emission control) system to prevent backfiring during the period immediately following sudden deceleration by diverting the air coming from the air pump away from the exhaust ports. Otherwise the exhaust gases which contain unburned gasoline could mix with fresh air and cause unwanted backfiring.

Also see air bypass valve

Antifreeze  A substance (usually ethylene glycol) mixed with water, and added to a vehicle's cooling system, to prevent freezing of the coolant in winter.

Antifreeze also contains chemicals to inhibit corrosion 

and the formation of rust and other deposits that would tend to clog the radiator and coolant passages and reduce cooling efficiency.

Most commercially available antifreeze contains ethylene glycol, a chemical that helps to control the temperature of the water in a vehicle’s radiator. During its life in a vehicle, antifreeze may become contaminated with fuel or heavy metal particles and grit. If the levels of dissolved metals, such as lead or cadmium, are high enough, used antifreeze may be a hazardous waste.

Do not dispose of antifreeze down the drain, in sewers, or into streams. Never drain the antifreeze from your car onto the street. The sweet smell of antifreeze is appealing to dogs and cats, who may drink it. Antifreeze is poisonous to animals — even a small amount can kill them.

CHEMICAL CONSTITUENTS: Ethylene glycol, Lead, Toluene 

Here are some waste reduction tips:

Reduce the amount of antifreeze you use by routinely checking the radiator, reservoir, and hoses for leaks and repairing them immediately.

Avoid overfilling the radiator or reservoir. 

Extend preventive maintenance (PM) cycle. As long as a chemical analysis or an antifreeze tester reveals that your antifreeze is doing its job, don’t drain and replace it.

Do not drain antifreeze into the street, into storm drains, or onto the ground. 

Use dedicated equipment and containers to collect and store used antifreeze to avoid contamination.

Recycle used antifreeze by sending it off-site for recycling, or contracting with an on-site recycling service. Specify a totally enclosed system.

Anti-Knock Agent A substance like tetraethyl lead which is added to gasoline to raise the octane number and reduce the gasoline's tendency to detonate, knock, or ping. In unleaded gasoline, tetraethyl lead is not used because of its environmental danger.

Anti-Lock Brake System  (ABS) Sometimes called "anti-skid brakes." A device which senses that one or more of the wheels are locking up during braking. It monitors the rotational speeds of the wheels and reduces hydraulic pressure to any wheel it senses locking up.It is controlled by both mechanical and electronic components. When you apply the brakes, the ABS will regulate the flow of brake fluid being delivered to the brake calipers. It must be remembered that a wheel cannot be steered unless it is rolling; so if the wheel is locked up, there is no steering control. By the use of electronic computers, the brakes rapidly alternate (at a rate of 30 times per second) from full pressure to full release. This process will also alternate from the left-front wheel and the right-rear wheel and switch to the right-front wheel and left-rear wheel. In this way both maximum braking and maximum steering control is allowed during braking. Before the advent of ABS, drivers were advised to pump the brakes to maintain the same effect. However, the human foot cannot pump the brakes faster than the computer control. Also, steady application of the brakes without ABS may cause brake failure (brake fade) because of the excess heat. Never pump the brakes if you have ABS. When you firmly apply the brakes with ABS, you may feel a pulsing sensation and hear a banging noise. The abbreviation ABS comes from the German anti blockier system.

Anti-Roll Bar Sometimes called the "anti-sway bar," "stabilizer bar," or

even (incorrectly) "roll-bar." It is usually a round bar which connects the left wheel suspension assembly with the right side. It may be found at the front and/or rear. Its main function is to keep both wheels rolling at the same rate when meeting bumps; but it also affects handling. A front anti-roll bar increases understeer and a rear bar increases oversteer.

Anti-seize compound  A coating that reduces the risk of seizing on fasteners that are subjected to high temperatures, such as exhaust manifold bolts and nuts.

Anti-Skid ( ASBS) A computer controlled automotive device which senses when one or more of the wheels are locking up during braking. It eases up on the amount of hydraulic pressure to that wheel. It must be remembered that a wheel cannot be steered unless it is rolling; so if the wheel is locked up, there is no steering control. By the use of electronic computers, the brakes rapidly alternate from full power to none so that both maximum braking and maximum steering control is allowed. If you jam on the brakes, you will feel a pulsing sensation. Sometimes called "anti-lock brakes."

Arm  A suspension linkage formed in the shape of an "A" or "V" found commonly on the front suspension. The sides of the two legs of the A-arm

are connected to the chassis by rubber bushings and the peak of the A-arm is attached to the wheel assembly. In this way, the wheel can freely move up and down. Sometimes there is an upper A-arm, a lower A-arm, or both upper and lower A-arms. The British call it a "wishbone."

Asbestos  A natural fibrous mineral with great heat resistance, commonly used in the composition of brake friction materials. Asbestos is a health hazard and the dust created by brake systems should never be inhaled or ingested.

Asymmetrical Tread The tread of a tire which has different shapes/patterns and sizes of grooves in the same tire. Often they are divided into three distinct patterns: The outside shoulder, the center zone, and the inside shoulder. The outside shoulder tread will have larger shoulder elements with very few sipes to provide increased cornering stability.

The center tread zone enhances steering control. The inside shoulder tread zone provides additional traction because the shape of the tread elements, sipes and larger shoulder slots help disperse water and slush.

Obviously these tires must be mounted only one way so that the outside pattern is actually on the outside of the wheel.

Automatic Choke  A device attached to the carburetor that automatically reduces the amount of air entering the carburetor by sensing changes in engine temperature. It is usually controlled by a coil spring which changes length as the engine is warmed or cooled.

Automatic Transmission A transmission that shifts its own gears according to the prevailing speed, load, and road condition. Also called automatic gearbox. Operation can be electrical or hydraulic

An Automatic Transmission a mechanism of the drivetrain which takes the power from the engine and transfers it to the driveshaft or wheels.

Without using a clutch, it uses a torque converter and fluid coupler to change the gear ratio. It automatically effects gear changes to meet varying road and load conditions.

Gear changing is done through a series of oil operated clutches and bands.

Automatic transmission has made driving a lot easier to drive and than manual transmission. The best part is that you don't have to use a clutch pedal or gearshift lever. An automatic transmission manages all of this on its own. Automatic transmissions automatically change to higher and lower gears with changes in the car's speed and the load on the engine. These transmissions are also aware of how far down you have pushed the gas pedal, and shift accordingly.

The output shaft turns the governor. The rolling of the governor is directly proportional to the speed of the car. The centrifugal force from the governor sends the oil is sent from the pump to the shift valves. The shift valves then move out sending the transmission fluid to the gear shifting mechanisms in the transmission. When the car slows down, the valves move in and send the transmission fluid in the opposite direction, thus changing the gears. The different gears are selected by routing the pressure to the clutches and brake bands

Automatic Transmission Fluid ( ATF) A very thin viscosity liquid designed for use in automatic transmissions to transfer the movement of the torque converter to the driveshaft.

 However it is also recommended for use in the forks of motorcycles. When poured into the throat of an automobile carburetor, it helps to remove a build-up of carbon on the cylinder head and the domes of pistons


Automatic Voltage Regulator  A voltage regulator which automatically holds the voltage of a distribution circuit or an alternator constant within certain limits, or causes it to vary in a predetermined manner.

AWD Acronym for All Wheel Drive

Axle  A shaft on which a wheel revolves, or which revolves with a wheel. Also, a solid beam that connects the two wheels at one end of the vehicle. An axle which also transmits power to the wheels is known as a live axle.

Axle Housing The large metal container for a rear-wheel-drive vehicle's axles, differential and ring and pinion gear. (Four-wheel-drive vehicles have a similar setup at the front, as well.) The bottom of the differential, often called a pumpkin, is usually the lowest point on a vehicle.

Axleshaft  A single rotating shaft, on either side of the differential, which delivers power from the final drive assembly to the drive wheels. Also called a driveshaft or a halfshaft.


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The objective of this Web Page is to familiarize you with basic auto maintenance
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