Glossary

| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V |W | X | Y | Z |

A

Accumulator – reservoir that stores fluid or gas under pressure

Actuator – device that moves as a result of an electrical signal

Aftermarket – related to servicing or replacement

Air injection – pollution control system that reduces hydrocarbon and carbon monoxide emissions by injecting air into the exhaust ports for more complete combustion

Anchor pin – drum brake component that holds the secondary shoe in place when brakes are activated

Anti-oxidation additive – chemical that reduces a liquid's ability to absorb oxygen and thicken

Anti-seize compound – chemical that prevents two parts from rusting together

B

Backing plate – round, metal plate that holds drum brake components in place

Baffle – metal plate that interferes with the flow of exhaust gas to reduce noise

Ball socket – connection that permits part movement in multiple directions

Band – coarsely-lined, metallic strap, in an automatic transmission, that tightens to stop the rotation of a planetary gearset

Bearing(s) – friction-reducing component that surrounds a spinning part

Bezel – retaining ring that holds a stationary component in place

Bleeder screw – screw that releases air from the hydraulic brake system

Blowby gases – exhaust gases, containing harmful contaminants, that escape past piston rings and into the crankcase and oil pan

Blower motor – fan that forces air from a heating and air conditioning system

Breaker point(s) – contact switches, which help step up battery voltage, within the distributor

Bridge claw – metal tabs of a wiper blade arm that hold the rubber blade insert in place

Bypass – device that permits fluid to flow around, rather than through, a component

C

Caliper – disc brake assembly that permits the piston and brake shoes to impart a clamping action on a revolving rotor, thereby stopping the attached wheel

Camshaft – shaft containing cams, or lobes, that synchronizes valve operation with piston movement inside the engine cylinder

Centrifugal force – outward force experienced by a rotating object

Chamois – a soft, highly absorbent leather

Choke – a plate at the carburetor opening that assists in cold-starting by constricting air flow and therefore making the fuel/air mixture richer

Circuit breaker – electrical safety device, which can be reset, that breaks a circuit in the event of an electrical surge or short circuit

Clutch pack – series of steel plates and friction discs, found in a differential, that prevents wheel lockup

Cold enrichment system – fuel injection components that assist in cold-starting

Combination valve – brake system component that acts as both a metering valve and a proportioning valve

Compression – process of squeezing into a smaller space

Compression ratio – ratio of internal cylinder volumes with the piston at maximum downward and upward positions

Compressor – belt-driven pump that pressurizes a gaseous refrigerant and forces it through the air conditioning system

Compressor clutch – magnetically engaged friction device that operates the compressor

Computer control – central electronic apparatus that coordinates and manages numerous engine and vehicle operations

Condenser – in distributors with breaker points, a device that stores electrical charge to prevent arcing; in air conditioning systems, a component that converts refrigerant from a gas to a liquid, thereby releasing its heat

Connecting rod – metal arm that connects the piston to the crankshaft

Control arm – pivoting lever that connects the vehicle frame to the steering knuckle and therefore wheel

Control assembly – rod or cable and associated linkages that operate the parking brake cable

Control valve – device for regulating the flow of liquid or gas through an opening

Convex – outwardly curved

Core plug – a.k.a. freeze plug; safety device to prevent frozen coolant from potentially cracking engine block

Countershaft – geared shaft that transfers rotary motion from the transmission input shaft to the output shaft

Coupling – connection

Cowl – front portion of car body to which windshield is attached

Crankshaft – irregularly-shaped shaft that converts up and down piston movement into rotary motion

Cylinder – engine chamber in which piston moves and combustion takes place

Cylinder head – engine block attachment that includes valves and associated components

D

Damper – flap-like valve that regulates the flow of additional warm air into the engine

Dielectric compound – silicone-based substance that prevents contamination of electrical connections due to salt, moisture, dirt, or corrosion

Diode – electrical component that allows current flow in only one direction; used to convert AC (alternating current) to DC (direct current)

Distributor advance – mechanism that adjusts spark plug operation with engine speed to promote complete combustion

Draincock – T-shaped, threaded plug used to drain the radiator

Drive shaft – metal shaft that transmits rotary motion from the transmission to the differential

Dry refill capacity – refill capacity if reservoir could be completely drained

Dry steering – turning the steering wheel while vehicle is motionless

Dwell angle – amount of distributor rotation while the breaker points remain closed to build up voltage

Dynamic balance – balanced about the center of rotation and from side-to-side using a tire spinning machine

E

Electrode – exposed metal conductor through which current flows in a spark plug

Electrolyte – mixture of distilled water and sulfuric acid found in batteries

Electronic fuel injection – fuel management system where pressurized fuel injectors are electronically controlled

Electronic ignition – ignition system that utilizes electronic circuitry instead of conventional breaker points to build up and distribute voltage

Emission control – any of several pollution control devices associated with the fuel or exhaust systems

Engine block – basic structural element of an engine that contains the pistons and to which other components are attached

Engine vacuum – suction created at the intake manifold due to piston movement

Ethylene glycol – active ingredient in antifreeze

Evaporator – air conditioning system device that converts refrigerant from a liquid to a gas, thereby causing it to absorb heat and create cooling action

Exhaust manifold – series of metal tubes that connects the engine exhaust ports to a singular exhaust pipe

Expansion valve – air conditioning system device that reduces pressure in the liquid refrigerant before it enters the evaporator

F

Fan shroud – plastic enclosure, situated around the cooling fan, that directs air flow through the radiator

Feed wire – device providing main electrical supply

Filament – fine wire, which glows when conducting current, found inside of a bulb

Firewall – heat protective barrier between the engine and passenger compartments

Fitting – portion of a component to which another is connected

Flame front – moving boundary of a fuel/air mixture explosion

Flange – specially formed edge used to join parts

Flare nut wrench – a.k.a. tubing wrench; box wrench with nearly closed end to permit firm grasp of a fitting nut and reduce chance of stripping it

Flasher – electrical switch that repeatedly opens and closes a circuit, thereby producing continuous on and off action

Float – component which controls flow of fuel entering a carburetor

Flooded – condition where excess unburned fuel has accumulated in the intake manifold, engine cylinders or carburetor

Fluid clutch – device that transfers rotary motion through use of a fluid

Flywheel – large, heavy disc, at rear of crankshaft, that smoothes out power pulses from the engine

Friction disc – clutch component that transmits rotary motion from the flywheel to the transmission input shaft

Fuel pressure regulator – fuel injected system device that controls pressure at the fuel injector tips

Fuel/air mixture – combustible combination of air and vaporized gasoline

G

Gasket – sealing membrane that prevents fluid or gas leakage between two fixed parts

Glow plug – diesel engine heating device that assists in cold starts

Governor – apparatus that limits engine speed

Grease cap – dome-shaped cover that prevents contamination of wheel bearings

Grommet – eyelet made of firm material to protect an opening in a part surface

Ground – connection to a large, metal object, such as the body or frame, that acts as a common return point in an electrical circuit

H

Half shaft – short drive axle used in front-wheel drive vehicles

Halogen bulb – halogen gas-filled bulb that burns brighter than an ordinary incandescent bulb

Harmonic balancer – circular weight attached to the front of the crankshaft to reduce rotational vibration

Heat riser – a.k.a. exhaust manifold heat valve; valve that permits redirected exhaust gases to heat the intake manifold bottom, thereby quickening engine warm-up

Heat shield – protective covering over catalytic converter that prevent burns

Heat stove – metal shroud placed over the exhaust manifold to generate preheated air for the engine intake

Heater control valve – vacuum-controlled device that regulates the flow of coolant into the heater core

Heater core – a.k.a. water heater; miniature, radiator-like device that releases heat, absorbed by the coolant, into the passenger compartment

Hex head – a.k.a. Allen socket; bolt head with six-sided indentation that requires similarly shaped tool to tighten or loosen

Hub – central portion of a rotating disc or pulley

Hydraulic failure – total breakdown of fluid-operated system

Hydrometer – device that measures fluid density and interprets fluid condition

I

Idle mixture – appropriate fuel/air mixture at idle speed

Idle speed – engine speed without application of accelerator

Idler arm – steering linkage component, mounted on the vehicle frame, that supports the center link and tie rods

Idler pulley – pulley that does not drive a component but modifies belt routing instead

Ignition coil – electrical component (transformer) that increases battery voltage tremendously to operate the spark plugs

Ignition timing – relationship of spark plug operation to piston movement

Impact load – sudden force

Impeller – rotating, fan-like device that pumps fluid

Inboard – toward the center of the vehicle

Injection timing – relationship of piston movement to the injection of fuel in the engine cylinder

Injector coil – electrical device that controls fuel pulsation from the fuel injectors

Inlet heater hose – small diameter, rubber hose that carries coolant into the heater core

Intake manifold – central reservoir that guides air or fuel/air mixture into the engine cylinders

J

Jet – narrow opening that controls fuel consumption in a carburetor

Journal – highly machined section of crankshaft around which it rotates or to which connecting rods are attached

K

Kickdown – apparatus that causes an automatic transmission to downshift for fast acceleration when the accelerator pedal is floored

L

Lash – the clearance between the valve stem and rocker arm when the valve is closed; in gears, the amount of free play

Lifter – a.k.a. tappet; cylindrical metal device that converts the rotary motion of camshaft lobe into linear push rod motion

Lining – frictional contact component of a drum brake

Lobe – egg-shaped bump on camshaft

Locating pins – guide pin that controls disc brake caliper movement

Lock tab – metal clip that locks a removable component in place

Lug nut and bolt – fastener that attaches tire/wheel assembly to the vehicle

M

Machining – a.k.a. turning; grinding to an extremely smooth surface

Master cylinder – piston-operated pump that pressurizes fluid in the brake system, thereby activating the brakes

Metering valve – brake system component that ensures simultaneous application of disc and drum brakes when the brake pedal is depressed

N

Neutral safety switch – automatic transmission device that prevents the engine from being started if the transmission is not in neutral or park

Noise suppressor – device (capacitor) that smoothes electrical system voltages, thereby reducing radio interference

Normally aspirated – using uncompressed air, that is, not turbocharged or supercharged

O

O-ring – compressible rubber gasket, located in a groove and typically coated with fluid, that deforms slightly to form a tight seal

Operating temperature – stabilized coolant temperature during normal engine operation

Outboard – toward the outside of a vehicle

Outlet heater hose – small diameter rubber hose that carries coolant away from the heater core

Overrunning clutch – clutch that operates in only one direction

Oxidize – process through which a substance absorbs and combines with oxygen

Oxygen sensor – a.k.a. exhaust gas sensor; emission control that monitors the oxygen content of exhaust gas so the computer control can make fuel/air mixture adjustments

P

Pad – disc brake frictional contact component typically made of a metallic or organic compound

Phillips head – screw with X-shaped groove in head

Pilot bearing – clutch component that supports the front of the transmission input shaft inside the rear of the crankshaft

Pinion gear – small gear that drives a larger gear at slower speed; for example, the starting motor gear rotates a flywheel to start the engine

Piston – cylindrical-shaped metal head that moves with expanding or contracting gas or fluid

Piston ring – seal that provides tight clearance between a piston and cylinder wall

Pitman arm – metal shaft that converts rotary motion of steering gear box output shaft to linear motion of the steering linkage

Planetary gear – complex automatic transmission gear assembly where small (planet) gears rotate around a large, central (sun) gear

Plasticizer – chemical additive that makes a material more flexible

Ply – a.k.a. inner cord; flexible, fibrous membrane that provides tire with structural support

Point gap – clearance between the two fully opened breaker points in a conventional ignition system

Polarity – relationship between negative and positive terminals or poles

Port fuel injection – a.k.a. multi-point fuel injection; fuel delivery system where each engine cylinder's intake port has a separate fuel injector

Pressure check valve – device that permits fluid flow in one direction, thereby keeping the system free of air or contaminants

Pressure control valve – apparatus that directs fluid flow in a power steering system

Pressure plate – clutch component that engages or disengages the friction disc and flywheel

Primary shoe – drum brake shoe facing the front of vehicle; usually smaller than the secondary shoe

Proportioning valve – brake system device that equalizes disc brake and drum brake stopping power, thereby preventing rear tire skidding in quick stops

Push rod – small, metal shaft that transfers linear motion from the lifter to the rocker arm; in a brake system, the shaft connecting the brake pedal with the master cylinder piston

R

Receiver-drier – air conditioning system device that accumulates excess refrigerant and removes moisture

Refrigerant – air conditioning system chemical that absorbs and releases heat

Relay – electromagnetic switch that opens or closes a circuit

Release fork – clutch component that forces the pressure plate into the friction disc, thereby engaging flywheel

Release lever – component, attached to the clutch pedal by a cable, that activates the release fork and initiates clutch action

Resonator – tubular exhaust system device that absorbs exhaust gas pulsation, thereby reducing noise

Rheostat – electrical device with adjustable resistance

Ring gear – in a transmission, the toothed circumference of a flywheel; in a differential, the large gear driven by the pinion gear

Rocker arm – small, pivoting lever that operates the engine exhaust or intake valves

Rolling resistance – natural tendency of loaded tire to resist flexure and therefore rotational movement

Runout – warp in a disc-shaped object that causes wobble while spinning or prevents it from laying perfectly flat

S

Seal – collar that prevents fluid or gas leakage between moving parts

Sealing bead – a.k.a. fitting flange; ring-like protrusion on fitting, which provides a tight interior seal with attached hose

Seating – wearing in such a way, from first use, that the two friction surfaces perfectly match

Secondary shoe – drum brake shoe facing the rear of vehicle; usually larger than the primary shoe

Self-adjuster – drum brake mechanism that maintains a constant gap between the drum and lining surfaces as the linings wear

Sending unit – mechanical sensing device that observes a given condition and transmits an electrical signal to a dashboard gauge

Service valve – air conditioning system access point that allows refrigerant maintenance activities

Servo – small device that assists in the operation of a larger apparatus

Shift fork – pronged, manual transmission device that engages a synchronizer to change gears

Shimmy – side-to-side wheel wobble caused by dynamic imbalance

Sight glass – transparent view port that permits observation of a liquid or gas condition

Sludge – gel-like oil formations caused by contaminants

Solenoid – magnetic plunger switch that controls the operation of another device

Spark plug socket – special wrench socket that completely fits over an exposed spark plug and has a rubber insert to grasp the spark plug terminal for removal

Specific gravity – the density of a fluid relative to water

Spider gear – small, beveled gear that drives a rear axle

Spindle – short, metal shaft on which wheel bearing rotates and supports wheel

Spline – parallel ridges on a shaft surface that allow any attached component sliding, but not rotational, motion

Stabilizer bar – a.k.a. sway bar; metal rod that connects control arms, thereby reducing body lean in turns

Star wheel – main component of the drum brake self-adjuster

Starter drive – output shaft of starter motor

Static balance – balanced about the center of rotation (but not side-to-side) using a bubble balance

Steering arm stop pads – cushions that prevent excessive steering linkage movement

Steering knuckle – apparatus that has a spindle and connects the wheel to remainder of suspension system through the ball joints

Steering shaft – metal rod that transfers rotary motion from the steering wheel to the steering gear

Striker bolt and plate – rod and latch mechanism used to secure door, trunk or hood

Strut rod – metal shaft, attached to vehicle frame, that limits lower control arm movement

Supercharged – intake system modified to ingest additional air from a belt-driven air pump and therefore produce more engine power

Synchronizer – manual transmission component that prevents gear grinding during shifts

T

T-fitting – T-shaped device that connects three hoses

Temperature sensor – device for measuring engine coolant or air intake temperature so computer control can adjust fuel/air mixture

Terminal – metal stub that serves as electrical connection

Thermostatic control – air conditioning system device that turns off compressor when evaporator becomes too cold

Throttle body – portion of air intake system that contains the throttle and is connected to the intake manifold

Throttle linkage – series of rods and pivot mechanisms that operates the throttle

Throttle position sensor (TPS) – electrical device (rheostat) that helps the computer control continuously adjust the fuel/air mixture

Throttle valve – flap-like device, connected indirectly to the accelerator pedal, that controls the flow of air into the engine

Timing belt – cogged, or toothed, belt that transfers rotary motion from the crankshaft to the camshaft

Timing gear – either of two matched gears located on the front ends of the crankshaft and camshaft

Tire/wheel assembly – tire and wheel combination as one unit

Torque – rotational or twisting effort

Torque converter – component (fluid clutch) that engages or disengages the engine and automatic transmission

Torque wrench – special tool that measures the tightness of a nut or bolt; prevents excessive tightening that damages parts or inadequate tightening that permits part failure

Torx head – screw head with a star-shaped indentation that requires similarly shaped tool to tighten or loosen

Tower – distributor cap projection that passes current from the underlying rotor to the attached spark plug wire

Transaxle – component, commonly found in front-wheel drive cars, that acts as both a transmission and differential

Transmission pan – lower portion of transmission that serves as a fluid reservoir

Transmission shift linkage – series of rods and pivot mechanisms that connects the shift lever to the transmission

Turbocharged – intake system modified to ingest additional air from an exhaust-driven air pump and therefore produce more engine power

V

Vacuum modulator – automatic transmission component that controls shifting action based upon engine load

Vacuum motor – a.k.a. vacuum diaphragm; temperature-controlled air cleaner attachment that operates an air flow valve

Valve – component that controls the flow of fuel/air mixture into, or exhaust gas from, the engine cylinder

Valve body – bottom portion of automatic transmission that contains numerous valves and fluid controls

Valve core – spring-operated valve, contained inside valve stem, that controls tire inflation and deflation

Valve cover – cylinder head covering that encloses the valves and associated components

Valve train – interconnected components that operate the engine valves

Vapor lock – stoppage of fluid flow due to formation of bubbles caused by high temperature or low pressure

Volatility – a measure of the ease with which a liquid vaporizes or evaporates

Voltage leak – unintended passage of electrical current through conductor or defective insulator

W

Water jacket – engine block and cylinder head cavities through which coolant circulates to absorb heat

Wheel cylinder – drum brake component that contains fluid and activates the brake shoes

Wheel rim width – depth between interior edges of wheel, or approximate height of wheel when laid on its face

Wire feeler gauge – tool, composed of a series of short wires of known diameter, that is used to measure small gaps

Y

Yoke – broad, U-shaped support, located at end of a shaft, that is a portion of the universal joint

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