ASE Vocab terms

brake fluid

A fluid under pressure in a hydraulic brake system. When the brake pedal is depressed, it activates a master cylinder to pump fluid through the brake lines to each wheel, actuating the braking system.

engine diagnostic test used to compare the power output of all cylinders.

Cylinder leakage test

center support bearing

a bearing housed in a rubber insulator, which is mounted to the underside of a vehicle and used to support the driveshaft when more than one driveshaft is used.

diagnostic trouble code (DTC)

a code that represents and can be used to identify a malfunction in a computer controlled system.

carbon monoxide

a colorless, odorless gas, which is highly poisonous. Produced by incomplete combustion. Absorbed by the bloodstream 400 times faster than oxygen.

detergent

a compound of soap like nature used in engine oil to remove engine deposits and hold them in suspension in the oil.

Catalyst

a compound or substance that can speed up or slow down the reaction of other substances without being consumed itself In an automotive catalytic converter, special metals (platinum or palladium) are used to promote combustion of unburned hydrocarbons and reduce carbon monoxide.

Cupping

a form of valve damage in which excessive heat causes the head of the valve to become cupped because it cannot withstand the normal forces created when it seats.

check valve

a gate or valve that allows passage of gas or fluid in one direction only.

bushing

a liner, usually removable, for a bearing; an anti-friction liner used in place of a bearing; a type of bearing that is used to support rotating shafts.

disable

a microcomputer decision that results in an automotive system being deactivated.

Compound

a mixture of two or more ingredients.

carbon

a nonmetallic element that forms in an engine's combustion chamber when oil is burned.

circuit

a path through which electricity flows before returning to its source.

coefficient of friction

a relative measurement of the friction developed between two objects in contact with each other.

differential pinion shaft

a shaft mounted inside the differential case that provides support and pivot for the differential pinion gears.

diode

a simple semiconductor device that permits flow of electricity in one direction but not the other.

Concentricity

a situation where a smaller circle is exactly in the center of a larger circle when measured in every direction. Valves will operate efficiently and give long service life only if the valve guide is concentric with the valve seat.

continuous injection system

a system that uses fuel under pressure to modulate or change the fuel injection area.

dial indicator

a tool used to measure small clearances; measurements are read on a dial.

drivetrain

all of the components that generate power and transfer that power to the wheels.

driveline

all parts connecting the engine to the driven axle.

computer

an electrical device that receives information from sensors and makes decisions based on these inputs along with programmed information and sends out decisions to actuators.

catalytic converter

an emission control device located in the exhaust system that contains catalysts, which reduce hydrocarbons, carbon monoxide and nitrogen oxides in the exhaust gases.

compression

an engine's ability to trap air and reduce its volume to create pressure. This ability is lost when engine parts such as piston rings and cylinders wear, or when valves lose their ability to seal due to burning or mechanical damage. Compression makes an engine fire smoothly (helps goo combustion) and operates efficiently. An engine compression test is one very effective way of measuring wear and checking for mechanical problems.

caster

angle formed by the relationship of the king pin axis and a vertical axis through the wheel center line when viewed from the side of the vehicle.

dropping resistor

battery voltage reduction device.

deflection

bending or movement away from the normal position due to loading.

disc brake

braking system that uses cast iron discs mounted on the wheel hubs, over which brake calipers are mounted. Hydraulic or air pressure from the brake system forces the caliper piston(s) against friction pads mounted in the calipers, which in turn clamp the brake discs, stopping their rotation.

disc brake rotor

cast iron disc mounted on the wheel hub, which is clamped by the caliper and disc brake pads to slow and stop its rotation.

dieseling

condition by which hot spots in the combustion chamber(s) cause the engine to run on after the key is turned off.

the number of electrons flowing past a given point in a given amount of time.

cylinder balance test

chafing

damage caused by friction and rubbing.

disc brake caliper

device in a disc brake system that is mounted straddling the brake disc. The caliper contains at least one piston and is used to provide clamping force of the brake pads on the disc.

Cylinder leakage test

diagnostic test where air is pumped through the spark plug hole. Air leaks at different points show the location of a compression leak.

closed loop

electronic feedback system in which sensors provide constant information on what is taking place in the engine. State of the engine control computer system when it is working normally, at full operating temperature and normal speeds with the oxygen sensor switching.

differential carrier

enclosure for the differential and ring and pinion gears.

combustion chamber

enclosure formed in the cylinder head at the top of the piston, where the spark plug ignites the compressed air/fuel mixture.

cylinder balance test

engine diagnostic test used to compare the power output of all cylinders.

constant velocity (CV) joint

flexible coupling that allows a shaft to maintain the same speed regardless of operating angle.

brake hose

flexible hose that connects the brake lines on the chassis with the calipers or wheel cylinders, or the junction block on a solid axle.

diaphragm

flexible, impermeable membrane on which pressure acts to produce mechanical movement.

brake shoes

friction material that is bonded or riveted to curved metal structures and attached to the backing plate by means of brake hardware. The brake shoes make contact with the brake drum to stop its rotation.

disc brake pads

friction material that is bonded or riveted to metal plates and mounted in the disc brake caliper. The brake pads are clamped against the disc brake rotor to stop its rotation.

direct injection

fuel injection system wherein fuel is sprayed directly into the combustion chamber.

differential

gear assembly that transmits power from the driveshaft to the wheels.

driveshaft

hollow metal tube that transfers power from the transmission to the differential.

differential case

housing for the differential pinion gears and side gears.

clutch

in a manual transmission, a device that allows the driver to engage and disengage the engine from the drivetrain; in an automatic transmission, a device capable of both holding and turning members of a planetary gear set; a device used to engage and disengage an NC compressor.

digital multimeter (DMM)

instrument that measures volts, ohms and amps and displays the results numerically.

data link connector

means through which information about the state of the vehicle control system can be extracted using a scan tool.

brake line

metal tubing that carries the brake fluid from the master cylinder to other brake system components.

coolant

mixture of water and ethylene glycol-based antifreeze that circulates through the engine to help maintain proper temperatures.

brake proportioning

optional safety-oriented system, for limiting drive axle brakes. Also, a system that varies individual axle braking effort in response to weight or other variable.

cross member

part of the vehicle frame structure, arranged transversely and attached to the frame rails at each side of the vehicle.

dowel

pin extending from one part to fit into a hole in an attached part; used for location and retention.

brake flushing

procedure to clean the brake hydraulic system with fresh, clean fluid that should be performed whenever new parts are installed or fluid is contaminated.

compression ratio

ratio of the volume in the cylinder above the piston when the piston is at bottom dead center relative to the volume in the cylinder above the piston when the piston is at top dead center.

contraction

reduction in mass or dimension; the opposite of expansion.

density

relative mass of matter in a given volume.

chemical cleaning

relies primarily on chemical action to remove dirt, grease, scale, paint or rust.

clutch release bearing

sealed bearing unit that fides on a sleeve over the transmission input shaft, and acts on the pressure plate to disengage the clutch disc when the clutch release mechanism is applied.

CV joint

see constant velocity joint.

castellation

slots cut in a bolt head or nut flange through which a cotter pin is inserted to secure the fastener.

coil spring

spring steel rod wound into a coil that supports the vehicle weight while allowing suspension movement.

center link

steering linkage component, which attaches the pitman arm to the idler arm, tie-rod or crosslink.

control arm

suspension component that connects the vehicle frame to the steering knuckle or axle housing and allows the up and down movement of the wheels.

charging system

system that supplies electrical power for vehicle operation and recharges the battery.

core

the 'center of the radiator, made of tubes and fins, used to transfer heat from the coolant to the air.

cold cranking amps (CCA)

the amount of cranking amperes that a battery can deliver in cold weather.

camber

the attitude of a wheel in which, when viewed from the front, the distance between the tops and bottoms of the tires are different.

Combustion

the burning of the air/fuel mixture in side the cylinder.

corrosivity

the characteristic of a material that enables it to dissolve metals, other materials or burn the skin.

clutch pressure plate

the component that is used to hold the driven disc against the flywheel. The pressure plate is composed of a cover and coil springs, driving disc and release levers, or a diaphragm spring.

caliper

the damping device containing friction material mounted to pads. When actuated, the caliper applies braking force to both sides of the rotor.

drivability

the degree to which a vehicle operates properly, including starting, running smoothly, accelerating and delivering reasonable fuel mileage.

clutch fork

the device that moves the release bearing, activating the pressure plate.

charge

the electrical current that passes through the battery to restore it to full power.

centrifugal force

the force that pulls an object out ward when it is rotating rapidly around a center.

clutch facing

the friction material on a clutch disc.

drop (voltage)

the net difference in electrical pressure when measured on both sides of a resistance.

current

the number of electrons flowing past a given point in a given amount of time.

clutch disc

the part of a clutch that engages the driving motion from the flywheel and pressure plate assembly and transmits that motion to the transmission input shaft.

center of gravity

the point about which the weight of a vehicle is evenly distributed; the point of balance.

carbonize

the process of carbon formation within an engine, such as on the spark plugs and in the combustion chamber.

countersink

to cut or form a depression to allow the head of a screw to go below the surface.

counter bore

to enlarge a hole to a given depth.

dilution

to make thinner or weaker. Oil is diluted by the addition of fuel and water droplets.

dainpen

to slow or reduce oscillations or movement.

chase

to straighten or repair damaged threads.

concentric

two or more circles which have a common center.

combination valve

unit in the hydraulic brake sys tem that incorporates the metering and proportioning valves in conjunction with the pressure differential switch.

cooling system

used to remove excess heat from an engine and transfer the heat to the atmosphere. Includes radiator, cooling fan, hoses, water pump, thermostat, and coolant passages.

bracket

used to secure parts to the body or frame.

circuit breaker

uses a heat-sensitive spring to break contact in an overload condition. Automotive circuit breakers will reset to close the circuit when they cool off.

crankshaft position sensor (CKP)

usually mounted internally in the engine that informs the ECM of crankshaft po.si ion, location of No. 1 piston, and crankshaft speed fat ignition timing.

dial caliper

versatile instrument capable of taking inside, outside, depth and step measurements.

digital

voltage signal that uses on and off pulses.

counterweight

weight forged or cast into the crank shaft to reduce vibration.