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Ha     He     Hi     Ho     Hu     Hy

Halogen lamp A high-output, white-light lamp used as a headlight. Also known as halogen light.

Halfshaft  A rotating shaft that transmits power from the final drive unit to a drive wheel, usually when referring to a live rear axle.

Hard Pedal 

1. A loss in braking efficiency so that an excessive amount of pressure is needed to actuate brakes.
2. A condition whereby the load literally overrides the brakes. 

Harmonic Balancer  A device designed to reduce torsion or twisting vibration in the crankshaft. May be incorporated in the crankshaft pulley. Also known as a vibration damper.


1. That part of an engine that covers the top of the cylinders and pistons and usually contains the combustion chambers and valve train.
2. That part of a compressor that covers the valve plates and separates the high side from the low side of an air-conditioning system.

Head Gasket  A gasket that is used to enhance sealing between a cylinder head and an exhaust manifold or header.

Headers  A header is a different type of manifold; it is made of separate equal-length tubes.

Headlights  Headlights are mounted on the front of the car to light the road ahead during night or foggy days. They have reflectors and special lenses and are usually the sealed beam construction type, with the filament, reflector and lens fused together into an airtight unit. The most popular type of headlight is the halogen type, because it provides bright illumination. The halogen bulb is filled with pressurized gas (halogen) and can produce flying fragments if shattered. Wear protective glasses for changing a halogen lamp and always throw out the old one in the protective carton that comes with the new one.

Heat Exchanger The "heat exchanger" is a device that uses exhaust heat to aid in fuel evaporation. It usually is built into the intake manifold as an area where the hot exhaust gasses and fuel-air mixture come close to each other.

Heater Core The heater core is a smaller version of the radiator that is used to keep your toes warm when it's cold outside. It is mounted under the dashboard. Some of the hot coolant is routed through this little radiator, by more hoses. A small electric fan is also mounted there especially for the purpose of directing the heat inside the car. The principle is exactly the same as the one used in the radiator for your engine, except that the heat is released inside the car instead of outside.

Helical Gear  A gear in which the teeth are cut at an angle to the shaft. The advantage is that there are usually two teeth meshing at all times, making for smoother and quieter operation.

Hemi  Slang term for an engine with hemispherical combustion chambers which allow for larger and less shrouded valves. Used in many sports and racing cars.

Hemi-Head  A hemispherically shaped combustion chamber at the top of the engine cylinder. The hemispheric shape provides improved efficiency because the forces of the explosion are directed to the piston by the curved surface of the combustion chamber.

High-Performance Tire  A tire with serious traction capabilities, usually for both straight-line acceleration and cornering performance. Many high-performance tires feature a soft rubber tread compound, which enhances traction but can shorten the tire's lifespan. Of course, people who are in search of optimum traction usually are willing to sacrifice a bit of tire longevity, as well as some performance in rain and snow.

Hone  An abrasive tool for correcting small irregularities or differences in diameter in an engine cylinder, brake cylinder, etc.

Hood  The removable or lift-up part of an auto body that covers the engine and allows access to it.
The car's hood consists of an inner and an outer panel. The inner panel provides strength, while the outer panel is just a metal cover. The underside of the hood is often covered with a sound-absorbing material. Some high performance cars have 'hood scoops' which channel outside air directly to the air filter, which gives improved performance and efficiency. The hood release is a small lever, which is usually mounted under the dash. It is connected to the hood latch by a cable. The hood latch has a safety feature, which requires a second latch to be released before the hood will open. This is to prevent accidental opening while driving.

Horsepower (hp.)  The unit for measuring the power output of an engine. One horsepower is defined as lifting 33,000 pounds one foot per minute.

Horn A device for sounding an alarm. On some entry level vehicles, a single horn makes a high pitch beep. On more expensive vehicles, the sound is made with two or more horns. The sound is made by an electrical charge which activates and deactivates a coil. The sound is then magnified by the shape of the horn. Large truck horns make a very loud noise because the sound is made by passing compressed air through the sounding device. A Claxton horn makes a sound that resembles the word "A-hoo-gah."

Hubcap  Often used as a synonym for wheelcover. In more literal terms, a wheelcover covers the entire wheel, while a hubcap covers only the center of the wheel, or the hub. “Dog-dish” hubcaps are popular among enthusiasts who like a sleeper look, and they often were found on police cars of the ’60s and ’70s.

Hydraulic  A mechanical operation based on incompressibility of liquids, generally oil and sometimes water, and their ability to offer resistance when being forced into a small cylinder or through an orifice, thereby transmitting an increase in applied force. Hydraulic brakes and clutches use this principle.

Hydraulic Assisted Brakes  See brake booster.

Hydraulic Brakes See brake booster.

Hydraulic Brake Booster hydraulic pressure supplied by the power steering pump, or a separate hydraulic pump, which is used to assist in applying the brakes; used on cars and on some trucks

Hydraulic Assisted Brakes  Brakes operated by hydraulic pressure.      See brake booster.

Hydraulic Braking System: Brakes operated by hydraulic pressure

Hydraulic Tappet  A tappet that utilizes hydraulic pressure from the engine's lubrication system to maintain zero clearance (constant contact with both camshaft and valve stem). Automatically adjusts to variation in valve stem length. Hydraulic tappets also reduce valve noise.

Hydraulic Valve Lifter  Valve lifter using hydraulic oil pressure to operate and capable of maintaining zero clearance between metal parts. Thus, valve noise and wear are considerably reduced as are the periodic valve adjustments.

Hydroplaning  A wet-weather phenomenon in which a vehicle's tires ride upon a thin layer of water and lose contact with the road surface. Tires typically are designed with grooves or water channels to prevent hydroplaning.

Hypoid Gears  A type of differential final drive using a spiral bevel gear on the drive shaft, allowing it to be located below the center of the ring gear on the axle. This makes possible a lower floor in the car.


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The objective of this Web Page is to familiarize you with basic auto maintenance
-  in some common emergencies -
not to make you an expert in auto mechanics

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