Dictionary of Automotive Terms Abbreviations

DICTIONARY OF AUTOMOTIVE TERMS - "Di"

DI

Acronym for direct ignition -- a system where each spark plug has its own ignition coil, thus eliminating the need for a distributor
Acronym for Distributor Ignition (System)

Diac: A two-lead alternating current semiconductor that allows current to flow in both directions at a preset voltage.

Diagnosis: Refers to use of instruments to determine cause of improper function of parts or system of a vehicle

See
fault diagnosis
self-diagnosis

Diagnostic: See
engine diagnostic connector
on-board diagnostic system

Diagnostic center: A garage or part of a garage where problems with a vehicle or part of a vehicle are determined.

Diagnostic code

Code displayed on instrument panel which can be used to determine area in system where malfunction may be located.
Code numbers obtained by accessing the diagnostic mode of the engine management computer. This code can be used to determine the area in the system where a malfunction may be located

Diagnostic computer: A computer terminal or engine analyzer which is hooked up to the car's electronic box and reveals the condition of the engine and various sensors.

Diagnostic connector: See
engine diagnostic connector

Diagnostic link: The electric cord which connects the computer terminal to the socket on the vehicle.

Diagnostics: The process of identifying the cause or nature of a condition, situation, or problem to determine the appropriate corrective action to take in the repair of an automotive system.

Also See
on board diagnostics

Diagnostic socket: A socket on the vehicle (usually found in the engine compartment) which is part of the onboard electronic sensor system.

Diagnostic system: The various sensors and electronic devices which record the operation of a number of functions within the vehicle.

Also See
on-board diagnostic system

Diagnostic testing: The analysis of the various functions of the components of a vehicle to determine if they are operating properly or have recorded faults which need to be corrected.

Diagnostic test modes: Various levels of diagnostic capabilities in OBD (on-board diagnostic) systems. These may include different functional states to observe signals, a base level to read diagnostic troulble codes, a monitor level which includes information on signal levels, bi-directional control with on/off board aids, and the ability to interface with remote diagnosis.

Diagnostic trouble codes

A numeric identifier for a fault condition identified by the on-board diagnostic system.
A number stored by the ECU when it detects a failure in a particular electrical circuit or mechanical system it is capable of monitoring. This number is a useful guide for repairing a problem.

Also See
diagnostic code trouble codes

Diagonal: Also See
heavy-duty diagonal cutting pliers
high leverage diagonal cutting pliers

Diagonal belt: Another term for shoulder belt

Diagonal brake system: A dual brake system with separate hydraulic circuits connecting diagonal wheels together (right front to left rear and left front to right rear)

Diagonal cutting: See
heavy-duty diagonal cutting pliers
high leverage diagonal cutting pliers

Diagonal cutting pliers: See
high leverage diagonal cutting pliers
heavy-duty diagonal cutting pliers
high leverage diagonal cutting pliers
heavy-duty diagonal cutting pliers

Diagonal split braking system: A dual-circuit braking system in which each circuit brakes one front wheel and the diagonally opposite rear wheel, so that in the case of failure of one circuit reasonably balanced braking can be achieved. See dual brakes--especially the picture.

Diagonally split system: A dual-circuit braking system in which each circuit brakes one front wheel and the diagonally opposite rear wheel, so that in the case of failure of one circuit reasonably balanced braking can be achieved. See dual brakes--especially the picture.

Diagram: See
circuit diagram
indicator diagram
timing diagram
wiring diagram

Dial: The face (usually circular) of an instrument like a speedometer, tachometer, vacuum gauge, etc.

Dial caliper: Dial Caliper

A slide-type measuring device which registers on a dial the distance between two points

Dialed in

The action of fine tuning an engine or component to its peak capacity.
The ideal set up of a bicycle when everything works just right

Dial gage: See
dial gauge.

Dial gauge: A precision micrometer type instrument that indicates the reading via a needle moving across a dial face.

Dial indicator: A precision measuring instrument that indicates linear movement to a thousandth of an inch (.01mm) with a needle sweeping around a dial face.

Also See
dial gauge.

Dial torque wrench: Torque Wrench

A wrench usually with a socket end and which measures the torque of a nut-bolt fastener. It registers the value on a dial.

Diameter: The distance between one edge of a circular object to the other edge and passing through the center.

Also See
bead seat diameter
bore diameter
circle diameter
external diameter
inside diameter
internal diameter
major diameter
minor diameter
nominal diameter
nominal rim diameter
nominal thread diameter
outer diameter
outside diameter
overall rim diameter
pitch circle diameter
pitch diameter
rim diameter
thread diameter
valve diameter

Diamond frame

(DF)

The traditional men's bicycle frame the principal parts of which form a diamond shape.
Tubular-frame design for motorcycles common until WW II and derived from the bicycle layout. The engine cases often form part of the structure. In profile it resembles a diamond shape

Diamond star: The name of Chrysler Corporation which comes from the pattern of its emblem.

Diaphragm

A flexible cloth-rubber sheet that is stretched across an area thereby separating two different compartments. A diaphragm is used in pumps to create a pressure differential that causes a fluid to be pushed or pulled from one point to another. Some carburetors have no float bowl (i.e., Tillotsen), but use a series of diaphragms to pump gasoline into the engine.
A flexible partition used to separate two chambers or elements.
In air-conditioning system, a rubber-like piston or bellows assembly which divides the inner and outer chambers of backpressure regulated air conditioning devices.
In fuel system, a thin dividing sheet or partition which separates a housing into two chambers, one of which is usually vented to vacuum while the other is not; used in vacuum-controlled secondaries, anti-stall dashpots, and other carburetor control devices.

Also See
piston diaphragm
A rubber-like piston or bellows assembly which divides the inner and outer chambers of back-pressure regulated air conditioning devices

Diaphragm clutch: Another term for a diaphragm spring clutch

Diaphragm link: The arm which transmits the movement of the diaphragm and the distributor baseplate in a vacuum advance mechanism.

Diaphragm pump: A device which has a flexible diaphragm which moves forward and backward by a solenoid or other mechanical device to transfer fluid.

Also see
twin diaphragm pump

Diaphragm spring: Diaphragm Spring

A type of spring shaped like a disc with tapering fingers pointed inward or like a wavy disc, used in some clutches. In an automotive clutch the diaphragm spring is part of the clutch pressure plate. When the clutch is engaged, this spring forces the pressure plate against the clutch disc; driver effort through the clutch linkage overcomes the spring pressure to disengage it. A type of spring, shaped like a disc with tapering fingers pointed inward or like a wavy disc, used in some clutches. In auto application, the diaphragm spring is part of the clutch pressure plate. When the clutch is engaged this spring forces the pressure plate against the clutch disc.

Also See
clutch diaphragm spring

Diaphragm spring clutch: Click image to supersize
Diaphragm Spring Clutch

A common clutch used in most vehicles with manual transmission where a diaphragm spring keeps the pressure plate in contact with the friction plate

Diaphragm Type Valve: A device consisting essentially of an automatic valve actuated by means of the application of fuel pressure upon a flexible diaphragm.

Diaphragm Valve: A device consisting essentially of an automatic valve actuated by means of the application of fuel pressure upon a flexible diaphragm.

DIC: Acronym for Driver Information Center

Dichlorodifluoromethane: The chemical substance (CCl2F2) used in automotive air conditioning systems to absorb, carry, and release heat. A member of the fluorocarbon family. Usually referred to as refrigerant or R-12

Dickey: British term for rumble seat.

DICM: Acronym for Distributor Ignition Control Module

Die

One of a matched pair of hardened steel blocks that are used to form (by stamping, pressing, extruding, drawing or threading) metal into a desired shape.

Also See
bending die lower bending die
A tool for cutting threads.

Also See
tap and die set.

Die back: See
die-back.

Die-back: In a lacquer finish the loss of gloss after compounding, caused by continued evaporation of thinner.

Die cast: Manufactured by forcing molten metal into a die. Especially used of aluminum or an alloy.

Die casting

Formation of an accurate and smooth object by forcing molten metal, plastic, etc., into a die under pressure.

Also See
cast.
Process of molding low-melting-temperature metals in accurately shaped metal molds.

Dielectric: A material which is an electrical insulator or in which an electric field can be sustained with a minimum loss of power.

Dielectric fluid: Fluid with high electrical resistance.

Dielectric grease: A special grease which is applied to the ends of electric terminals to inhibit corrosion between the terminals or to be sure that there is good electrical contact between the terminals.

Dielectric silicone compound: A non-conducting silicone grease applied to spark plug wire boots, rotors, and connectors to prevent arcing and moisture from entering a connector

Diesel: A type of engine or fuel or oil used for that engine.

Also See
diesel engine
diesel_Fuel
diesel oil
turbo-diesel

Diesel cycle: A four-stroke cycle where the air is sucked into the cylinder and compressed at a ratio of up to 241. At the end of the compression stroke the fuel is injected. Because of the high compression and resulting increase in temperature, the fuel is ignited leading to the power stroke and followed by the exhaust stroke where the combustion products are removed.

Diesel-electric plant: A generating station that uses diesel engines to drive its electric generators.

Diesel engine: An internal combustion engine that uses diesel oil for fuel. The true diesel does not use a carburetor or an ignition system (i.e., spark plugs) but injects diesel oil into the cylinders when the piston has compressed the air so tightly that it is hot enough to ignite the diesel fuel without a spark. Because a cold engine cannot ignite the diesel fuel, glow plugs are used to heat the mixture, but they do not provide a spark. Named after Rudolf Diesel (1858-1913), the inventor.

Also See
compression ignition

Diesel fuel

A light oil fuel which has a relatively low ignition temperature. It is heavier than gasoline and uses the heat of extremely highly compressed air to ignite the fuel in the combustion chamber.
A fuel composed of distillates obtained in petroleum refining operation or blends of such distillates with residual oil used in motor vehicles. The boiling point and specific gravity are higher for diesel fuels than for gasoline.

Diesel fuel system: Diesel engines are internal combustion engines that burn diesel oil rather than gasoline. Injectors are used to spray droplets of diesel oil into the combustion chambers, at or near the top of the compression stroke. Ignition follows due to the very high temperature of the compressed intake air, or to the use of glow plugs, which retain heat from previous ignitions (spark plugs are not used). Diesel engines are generally more fuel-efficient than gasoline engines but must be stronger and heavier because of high compression ratios.

Diesel index: Product of the API gravity and the aniline point (in degrees Fahrenheit) of a Diesel fuel, divided by 100; an indication of the ignition quality of the fuel.

Dieseling: A form of autoignition in which a gasoline engine continues to fire after the ignition has been shut off. In late-model emission-controlled engines, dieseling or run-on is caused by heat and the unusually high manifold pressure that result from retarding the spark at idle.

Diesel knock: The noise caused by the rapid rise in pressure in a diesel engine especially when the engine is cold or running at a low speed. Also called "diesel rattle."

Dieselling: See
dieseling

Diesel oil: Fuel for cars with diesel engines. This is not a form of lubricating oil.

See
cetane rating.

Diesel Oxidation Catalyst: (DOC) Catalyst promoting oxidation processes in diesel exhaust. Usually designed to reduce emissions of the organic fraction of diesel particulates, gas-phase hydrocarbons, and carbon monoxide.

Diesel particulate filter: (DPF) A filter which removes small particles from a diesel exhaust. It looks like a honeycomb catalytic converter but acts as a mechanical separator. It prevents these particles from discharging in the tailpipe. Collected particulates need to be removed from the filter, usually by continuous or periodic oxidation in a process called "regeneration."

Diesel Particulate Matter

(DPM) Sub-micron size particles found in diesel exhaust. Most emission regulations specify DPM measurement methods in which particulates are sampled on filters from cooled exhaust gas. The cooling causes condensation of vapors in the gas sampling train. Thus, the DPM is composed of both solid and liquid particles and is generally classified into three fractions:

inorganic carbon (soot)
organic fraction (often referred to as SOF or VOF)
sulfate fraction (hydrated sulfuric acid)

Diesel rattle: Another term for diesel knock

Die set: See
tap and die set

Die stock: A tool used to hold and operate dies when cutting outside threads.

Die size: Retread rubber is designated by its crescent shaped dimensions in inches and eighths, and its thickness in 32nds of an inch; (e.g., 66-72-16; the crown would measure 6 and 6 eighths, the base 7 and 2 eighths wide; and the thickness 16/32 of an inch, or gauge of the stock rubber.)

Diff: A colloquial term for a differential

Differential

Click image to supersize
Differential

The temperature or pressure difference between cut-in and cut-out temperature or pressure of a control.
A unit on rear-wheel drive vehicles that takes the power of the rotating driveshaft at right angles to the rear axle and passes it to the axle. It will not only drive both rear axles at the same time, but will also allow them to turn at different speeds when negotiating turns. In this way the tires do not scuff or skid
In front-wheel drive cars, the differential is located in the transaxle, usually directly below the transmission.

Also See
automatic slip-control differential
axle differential
bevel differential
center differential
front differential
helical differential
inter-axle differential
limited-slip differential
limited slip differential
lockable differential
locking differential
lockup differential
multiple-disc limited-slip differential
no-spin differential
open differential
planetary gear differential
pressure differential switch
rear axle differential
rear differential
spur differential
torque sensitive limited slip differential
torsen differential
traction differential
variable limited-slip axle/center differential
visco-differential

Differential cage: The rotating metal container inside the differential housing and encloses the differential side gears and pinion gears. Also called the differential carrier

Differential carrier: See
differential cage

Differential case: The steel unit to which the ring gear is attached. The case drives the spider gears and forms an inner bearing surface for the axle and gears.

Differential casing: The differential housing

Differential gear: See
differential gears.

Differential gears: The gears that transmit engine power to the driving axles and are arranged so as to permit the rear wheels to turn at different speeds as required when the vehicle is negotiating a turn.

Differential grease: See
gear grease.

Differential housing: Differential housing

The enclosure which contains the differential gears.

Differential lock: A mechanism which eliminates the action of the differential so that both wheels can be driven for better adhesion on slippery surfaces.

Differentially: See
galvanize differentially

Differential pinion: The bevel pinion in the differential.

Differential pressure

The pressure difference between two regions, such as between the intake manifold and the atmospheric pressures. In Bosch KE-Jetronic systems, the difference between actuator fuel pressure in the lower chambers of the differential-pressure valves and the system pressure entering the pressure actuator.
The difference in pressure between the upper and lower chambers of a CIS fuel distributor

Also See
pressure drop

Differential pressure regulator

(DPR)

A pressure actuator
An electronically controlled valve which regulates the fuel flow to the lower chamber of the CIS fuel distributor

Differential pressure valve: Inside the Bosch CIS fuel distributor, these valves (there is one for each cylinder) maintain a constant pressure drop at each of the control-plunger slits, regardless of changes in the quantity of fuel flow

Differential pressure warning switch assembly: A unit to actuate a warning device indicating an undesirable pressure difference between the separate circuits of a brake system

Differential side gear: The bevel gear on either side of the differential into the center of which the axle shaft fits

Differential switch: See
pressure differential switch

Diffusing lens: The lens in the headlight glass which helps to focus the beam

Diffusion

The way in which innovations spread through market or non-market channels.
Mixing the molecules of two gases by thermal agitation
Movement of a species under the influence of a gradient of chemical potential (i.e. a concentration gradient).

Diffusive transport: The process by which particles of liquids or gases move from an area of higher concentration to an area of lower concentration.

Digifant: VW collaborated with Bosch to develop this electronic injection system. Digifant is similar to a Motronic system, except that its timing control map is less complicated than the Motronic map. And it does not have a knock sensor

Digifant II: A refined version of VW 's digifant. This system has some control improvements and uses a knock sensor for improved timing control

Digital: A signal that is either "on" or "off." In a computer, the signal is translated into binary digits 0 and 1 and is interpreted by the microprocessor as a voltage signal that is either "low" or "high," or current flow that is "on" or "off."

Digital caliper: A slide-type caliper which gives a digital readout.

Digital clock: A timing piece which reveals the time with a series of numbers rather than with sweeping pointers.

Digital computer: A computer that works with information in the form of fixed numbers, usually in binary code.

Digital filter: Electrical filter suitable for use with digital signals, i.e., those which are continuous with time. Contrast with analog filter.

Digital frequency control: (DFC) A system which automatically stabilizes or tunes the frequency of a selected radio station.

Digital fuel injection: (DFI) a GM system, similar to earlier electronic fuel injection system, but with digital microprocessors. Analog inputs from various engine sensors are converted to digital signals before processing. The system is self-monitoring and self-diagnosing. It also has the capabilities of compensating for failed components and remembering intermittent failures

Digital ratio adapter controller module: (DRAC) a device used on GM vehicles to convert the analog signal from the speed sensor into a digital signal that the EBCm can use

Digital speedometer: A speedometer which shows the speed in digital numbers rather than a needle on a dial gauge (which is called an analog speedometer).

Digital volt-ohm multimeter: (DVOM) a digital electronic meter that displays voltage and resistance

Dig out: To accelerate at top power.

Diluent: A fluid which thins or weakens another fluid.

Dilution: See
crankcase dilution.

Dilution air: Air which enters a draft regulator or similar device and mixes with the flue gases.

Dimethyl Ether: (DME) The simplest ether CH3-O-CH3. Can be manufactured from natural gas or from a renewable organic feedstock. DME is a prospective alternative diesel fuel.

Dimmer: A switch used to lower or dip the headlights from high beam to low beam and back again.

Also See
headlight dimmer switch

Dimmer control: A rotary control switch which will increase or decrease the intensity of the instrument lights. Also called interior dimmer light switch.

Dimming mirror: A vehicle mirror located within the passenger compartment above the windshield which can be switched to reduce the glare from the headlights of a vehicle approaching from behind. Some are activated automatically while others are engaged by a lever below the mirror.

Dimmer switch: A device used to lower or increase the brightness and focus of the headlights (i.e., from high-beam to low-beam). The British term is "dipswitch." Also called headlight dimmer switch

DIN: Acronym for Deutsche Industrie Normen (German industrial standards). DIN horsepower is similar to the SAE net horsepower. It is measured at the output shaft of an engine fully equipped with normal accessories.

Ding: A small dent in the surface of a panel

Dinging: The action of straightening a damaged panel by using a hammer and dolly to bring it back into shape.

Dingman: A colloquial term for a person who repairs body panels. A person who works in an automotive factory adjusting panels without damaging the paint

DIN mounting: The standard hole in the dash through which a DIN radio can be installed

Dino: Click image for books on
Ferrari Dino

A model of automobile manufactured by Ferrari

DIN radio: An aftermarket radio which fits into a thinner hole than most American radios. When installing a repacement radio, special faceplates are necessary

Diode

Two-element electron tube which will allow more electron flow in one direction in a circuit than in the other direction; tube which serves as a rectifier.
An electrical component having the ability to pass electric current readily in one direction but resisting current flow in the other. When four diodes are connected in a certain way (i.e., "bridged") they will convert AC to DC, thus becoming a rectifier.

Also See
rectifier diode
zener diode

Dion axle: See
de Dion axle

Dioxide: See
carbon dioxide

Dip

A British term for dimming the headlights.
A low horizontal indentation of the pavement which may cause a speeding vehicle to lose control.
To immerse.

Also See
full dip treatment
hot dip

Dipped beam: A British term for low beam

Dipper: A British term for the dimmer switch

Dipper switch: A British term for the dimmer switch

Dipping mirror: A British term for day-night mirror

Dipstick

The metal rod that passes into the oil sump it is used to determine the quantity of oil in the engine. The oil level is marked on the rod and matches level indicators on the rod. Dipsticks are used to check engine oil and transmission fluid. In most instances, the dipstick is inserted as far as it will go and then removed to check the level. In motorcycle engines, the dipstick is placed on the top of the threads (i.e., not screwed down) to check the level.
A stick that's dipped into a reservoir to check the level of the fluids based on the markings on the stick. Most common dipsticks are for used to check oil, transmission fluid, and power steering fluid.

Also See
oil dipstick

Dipswitch: A British term for the dimmer switch

Dip treatment: See
full dip treatment

Direct-acting shock absorber: A telescopic shock absorber.

Direct current: (DC) An electric current that flows steadily in one direction only. This is the type of current found in a battery and throughout the lighting and accessory system of a vehicle. Contrasts with alternating current (AC).

Direct damage: A vehicle damage caused directly by an impact with an object. In contrast with an indirect damage.

Direct digital control: (DDC) Use of digital computer to perform required automatic control operations in a total energy management system.

Direct drive: When the gearing is such that the crankshaft and driveshaft revolve at the same speed, the vehicle is in direct drive. Usually this occurs in high gear (except for those with overdrive). It is represented as 1.001 ratio.

Direct drive powertrain: A system of propulsion where the speed of the engine, transmission, and propeller shaft rotate the same.

Direct expansion evaporator: Evaporator using either an automatic expansion valve (AEV) or a thermostatic expansion valve (TEV) refrigerant control.

Direct ignition

(DI)

A system where each spark plug has its own ignition coil, thus eliminating the need for a distributor
In diesel engines with direct injection the combustion chamber is not divided and fuel is injected directly to the cylinder.

Direct ignition device: An igniter utilized to ignite gas at a main burner.

Direct ignition system

(DIS)

An ignition system which does not used a distributor but carries high voltage from the ignition coils directly to the spark plugs.
A system in which the ignition means functions to ignite the main burner gas directly and in which a flame sensing means or safety shutoff device senses main burner flames or the absence of main burner flames.

Also See
integrated Direct Ignition System

Direct injection: A fuel injection system which is generally used in diesel engines and forces fuel directly into the combustion chamber. It requires very high injection system pressure to overcome the pressure within the combustion chamber.

Also See
high speed direct injection

Direct internal reforming: Production of a desired product (hydrogen) within a fuel cell from a hydrocarbon based fuel (methanol, gasoline, etc.) fed to the fuel cell or stack.

Direct methanol fuel cell: (DMFC) A type of fuel cell in which the fuel is methanol (CH₃OH), in gaseous or liquid form. The methanol is oxidized directly at the anode with no reformation to hydrogen. The electrolyte is typically a PEM.

Directional baffle plate: Installed in a Quadrajet carburetor's secondary bores to help direct the airflow for improved distribution in the intake manifold

Directional stability: Ability of a vehicle to move forward in a straight line with a minimum of driver control. A vehicle with good directional stability will not be unduly affected by side wind, road irregularities, etc.

Directional tire: Directional designs are recognized by the grooves in the tread that swipe away in a backward angle from the center of the tread face and rotate in only one direction. A direction of rotation arrow is located on both sidewalls of the tire. Directional tires enhance straight-line acceleration, provide maximum dry traction, better wet performance which helps to reduce rolling resistance as well as providing shorter stopping distances.

Also See
asymmetrical tread
directional tread
Symmetrical

Directional tread: An arrangement of bars, grooves, and ribs on a tire's tread in any manner that gives most effective traction when the tire revolves in only one direction.

Also See
directional tire

Direction indicator: The signal lights which blink on either side of the front of the vehicle and either side of the rear of the vehicle. Some early cars (like the Austin and Flying Standard) had small illuminated arms that flipped out from the B-post instead. The purpose of signal lights is to warn other drivers of a change in direction when turning a corner or changing lanes.

Direction indicator warning light: A light on the instrument panel which flashes when the signal lights are operating. Usually this light is in the shape of a green arrow. On some cars, like Cadillac, a secondary light is mounted in a pod on the upper edge of each front fender and in a pod inside the cab above the backlight (i.e., back window)

Direction of rotation: The direction in which a wheel or shaft turns or is supposed to turn.

Direction of travel: The direction in which an object (e.g., a vehicle) is moving.

Direct polarity: Direct current flowing from anode (base metal) to cathode (electrode). The electrode is negative and the base metal is positive.

Direct-pull brake: A type of a very powerful centerpull bicycle brake used mostly on mountain bikes from the 1980s and early 1990s

Dirtbike: A motorcycle intended for off-road use that are not legal to ride on public roads. Sometimes the term "pure-dirt" is used to distinguish a dirtbike from a dual-sport motorcycle

Dirty town: Trucker slang for New York City as in "I got a load of garbage going to dirty town."

DIS

An acronym for direct ignition system or a distributorless ignition system similar to the C3I system, using two coils on four-cylinder engines
Acronym for Direct Ignition (Waste Spark)

Disabled

The condition of a vehicle which is not able to be driven because of a failure of some component (e.g., bad battery, flat tire, engine seized) or because of an accident.
A driver who lacks the use of a limb.

Disabler: See
ignition disabler

Disassemble: To take a vehicle or major component (e.g., the engine) apart in order to repair or restore the vehicle or component or to sell or recycle them. Also called "dismantle."

Disc

May be spelled "disk."

A flat dish-shaped item which may or may not have a center hole.
A parallel-faced rotating component of a disc brake system acted upon by brake pads to slow or stop the vehicle. Also called a rotor

Also See
abrasive disc
balance disc
brake disc
brake disc type
caliper disc
center locking disc
clutch disc
cutting disc
disc brake
fixed-caliper disc brake
floating caliper disc brake
four wheel disc brakes
friction disc
grinding disc
hardy disc
hinged-caliper disc brake
multi-disc
multiple disc clutch
multiple disc
padding disc
parking disc
pin slider caliper disc brake
plain disc wheel
rotary disc valve
tax disc
ventilated discs
wheel disc

Discard diameter

The diameter at which a worn brake drum should be replaced
The largest inside diameter at which a brake drum can safely operate.

Discard thickness: The thickness at which a brake disc should be replaced

Disc brake: Click image to supersize
Disc Brake

A type of brake that has two basic components a flat rotor (disc) that turns with the wheel and a caliper that is stationary. When the brake pedal is depressed, linkage (mechanical or hydraulic) causes the caliper to force its heat-resistant brake pads against both sides of the rotating disc thus slowing or stopping the wheel. Almost all new cars have disc brakes on the front wheels with drum brakes on the rear. More expensive cars have four wheel disc brakes. Because of the need for greater pressure to activate disc brakes, most cars so equipped also have a power booster. Wear takes place in the pads and the rotors. The pads are usually replaced while the rotors can sometimes be reground else they too must be replaced. If the rotors are not tightened correctly when installed, they can warp and cause a jerking motion when stopping.

Also See
brake, disc type
caliper disc brake
fixed-caliper disc brake
floating caliper disc brake
four wheel disc brakes
hinged-caliper disc brake
pin slider caliper disc brake
sliding-caliper disc brake

Disc brake gauge: A tool for measuring the thickness, wear, and score depth on brake discs

Disc brake pad: An assembly consisting of friction material and its steel backing

Disc brake rotor: See
brake rotor

Disc brakes: See
disc brake.

Disc clutch: See
multiple disc clutch

Discharge

The action of drawing electric current from the battery. The opposite action to charging.
To pour out liquid from a pump.
The product (e.g., the liquid) that is poured out of a pump.
To bleed some or all of the refrigerant from a system by opening a valve or connection to permit refrigerant to escape slowly

Also See
battery discharge controller
capacitive discharge
gas discharge headlight
gas discharge lamp
gas discharge light
gaseous discharge headlight
gaseous discharge lamp
main mixture discharge nozzle

Discharge air: Air conditioning air forced through the vents (ducts) into the passenger compartment

Discharge check ball: In a carburetor, a small check ball that lifts off its seat when the pump well is pressurized by the accelerator pump, which allows fuel to be discharged into the venturi through the shooter nozzle

Discharge controller: See
battery discharge controller

Discharged battery: A battery that cannot produce sufficient power.

Discharge headlight: See
gas discharge headlight
gaseous discharge headlight

Discharge ignition: See
capacitor discharge ignition system

Discharge indicator: See
battery discharge indicator

Discharge lamp: See
gas discharge lamp
gaseous discharge lamp

Discharge light: See
gas discharge light

Discharge line

In an air conditioning system, the line which connects the compressor outlet to the condenser inlet
The line which connects the compressor outlet to the condenser inlet

Discharge nozzle: In a carburetor, the end of the main delivery tube that discharges fuel into the venturi area.

Also See
main mixture discharge nozzle

Discharge pipe: The outlet pipe from a pump

Discharge plug: See
surface discharge plug

Discharge pressure

The pressure exerted in a liquid pumped, expressed in psi.
The (high side) pressure of the refrigerant being discharged from the air conditioner compressor

Discharge rate: Amount of current discharged from a battery, expressed in amps

Discharge side

Outlet side.
The part of the air conditioner system under high pressure, extending from the compressor outlet to the thermostatic expansion valve/tube inlet

Discharge valve

Valve on the outlet side of a reciprocating pump. The opposite is suction valve.
In an air conditioner system, a device used to check high side pressures, usually referred to as the high side service valve
A device used to check high side pressures. Usually referred to as the high side service valve

Discharge voltage: See
spark discharge voltage

Discharging current: Current supplied by a storage cell or battery, whose direction is opposite to that of the charging current

Discolor: To alter the color of (a finish, metal, etc.) to a color which is not wanted. This fading may be caused by sitting in the sun, drops of contaminants (tree sap, bird dropping, spilled gasoline), poor paintwork, etc.

Disconnect: To remove the terminal from a mechanical or electrical device or from the other side of the terminal. While some may be simply pulled apart, others have catches which must first be released.

Disconnect terminal: Solderless connectors in male and female forms, intended to be easily disconnected and connected. Typically, a blade or pin (male connector) fits into a matching receptacle or socket (female connector). Many components have built-in (blade) terminals that require a specialized female connector

Disconnect the battery: The action of removing the high tension electrical cables from the battery terminals. Also called "isolate the battery"

Discontinuity: See
absorption discontinuity

Discount: See
residual discount
manufacturer discounts

Disc runout: A condition in which the disc is no longer parallel and does not rotate in a true circle. Usually due to excessive heat, which warps the disc.

Disc sander: A round, rubber disc powered by an electric drill and covered with abrasive paper for rough sanding work.

Also See
orbital sander

Disc type: See
brake disc type

Disc valve: A type of rotary valve that allows the passage of fluid through an arc-shaped slot.

Also See
rotary disc valve

Disc wheel

A wheel constructed of stamped steel.
A rim and metal disc that have been welded together. The disc is usually offset from the centerline of the rim to allow for dual tire mounting and to provide sufficient clearance between the duals. Disc wheels are attached to the hub with either single nuts or double cap nuts.
Single-piece rim/wheel assembly of stamped and welded steel or forged aluminum, anchored by 8 or 10 nuts to a hub.

Also See
Budd Wheel
plain disc wheel
solid disc wheel

Disc wheel type: A type of dual mounting wheels where the discs are offset from the centerline of the rim to provide clearance between the tires. They are held in place by double cap nuts, inner cap nuts, and outer cap nuts.

Disengage: To move (a gear, dog clutch, etc.) so that it no longer meshes with another matching part

Disengage the clutch: During normal driving, the power of the engine is being transferred to the gears of a manual transmission because the clutch plates are pressed together. When you press down on the clutch pedal (or pull in the clutch lever on a motorcycle), you are releasing that contact (i.e., disengaging the clutch) so that there is no connection between the engine and the transmission. You engage the clutch when you release the pedal or lever.

Dish

A depression in the top of a piston.
Offsetting of the hub on a rear wheel on a derailleur bike to make room for the freewheel and still allow the wheel to be centered within the frame.

Also See
negative wheel dish
offset dish

Dished: A plate, washer, or disc is dished when the center is recessed from the rim like a shallow bowl.

Dished brake disc: A disc that has worn thinner at the inner part of its friction surface. This is an abnormal form of wear

Dished rotor: A brake rotor that is thinner at the inner edges of its friction surfaces. Dishing is a form of taper variation

Dishing: See
negative wheel dishing

Dish washer: A washer is a flat disc with a hole in the center. The disc in a dish washer is dished or bent in a concave fashion.

Disk: More commonly spelled "disc."

Dismantle: To take a vehicle or major component (e.g., the engine) apart in order to repair or restore the vehicle or component or to sell or recycle them. Also called "disassemble."

Dispersant: Dispersing or scattering in various directions; a state of matter in which finely divided particles of one substance (disperse phase) are suspended in another (dispersion medium) substance

Displacement: The total volume of air displaced by all the pistons in travelling from BDC to TDC, i.e., the total volume of air and fuel the cylinder can hold before compression occurs. Also called piston displacement."

Also See
cubic inch displacement
engine displacement
light displacement
loaded displacement
piston displacement
positive displacement compressor

Displacement compressor: See
positive displacement compressor

Displacement, piston: Volume obtained by multiplying area of cylinder bore by length of piston stroke.

Displacement taxes: A vehicle taxation system which determines the amount of taxes based on the engine displacement of the vehicle.

Displacement volume: That part of the cylinder capacity that is swept by the pistons on their up and down strokes (i.e., the volume through which a piston moves in one stroke) formed by the bore diameter and the piston stroke. Also called "swept volume."

Display: Any device that conveys information. In a vehicle, displays are either lights, gauges, or buzzers. Gauges may be analog or digita

Also See
compass display
graphic display unit
heads up display

Display unit: See
graphic display unit

Disposition: See
Natural gas disposition Petroleum disposition

Disposition fee: A fee you pay at the end of the lease, to the lessor, that covers the lessor's cost of getting the vehicle ready for sale after you have returned the vehicle. It is often applied against any deposit you made at lease inception.

Dissipate: Scattered in various directions

Dissolve: Transition from one scene to another in which the whole image of the first gradually disappears as it is replaced by the second

Distance: See
braking distance
reaction distance
stopping distance
trail distance

Distance piece: A collar or spacer which is placed between two parts to keep them the correct distance apart.

Distance to the sun: See
mean distance to the sun

Distillate: A product formed by heating a liquid in a vessel and collecting and condensing the resulting by-product(s).

Distillate fuel oil

A general classification for one of the petroleum fractions produced in conventional distillation operations. It includes diesel fuels and fuel oils. Products known as No. 1, No. 2, and No. 4 diesel fuel are used in on-highway diesel engines, such as those in trucks and automobiles, as well as off-highway engines, such as those in railroad locomotives and agricultural machinery. Products known as No. 1, No. 2, and No. 4 fuel oils are used primarily for space heating and electric power generation.

No. 1 Distillate: A light petroleum distillate that can be used as either a diesel fuel (see No. 1 Diesel Fuel) or a fuel oil. See No. 1 Fuel Oil.
1. No. 1 Diesel Fuel: A light distillate fuel oil that has distillation temperatures of 288°C at the 90-percent point and meets the specifications defined in ASTM Specification D 975. It is used in high-speed diesel engines, such as those in city buses and similar vehicles.
2. No. 1 Fuel Oil: A light distillate fuel oil that has distillation temperatures of 204°C at the 10-percent recovery point and 288°C at the 90-percent point and meets the specifications defined in ASTM Specification D 396. It is used primarily as fuel for portable outdoor stoves and portable outdoor heaters.
No. 2 Distillate: A petroleum distillate that can be used as either a diesel fuel or a fuel oil.
1. No. 2 Diesel Fuel: A fuel that has distillation temperatures of 260°C at the 10-percent recovery point and 338°C at the 90-percent recovery point and meets the specifications defined in ASTM Specification D 975. It is used in high-speed diesel engines, such as those in railroad locomotives, trucks, and automobiles.
2. Low Sulfur No. 2 Diesel Fuel: No. 2 diesel fuel that has a sulfur level no higher than 0.05 percent by weight. It is used primarily in motor vehicle diesel engines for on-highway use.
3. High Sulfur No. 2 Diesel Fuel: No. 2 diesel fuel that has a sulfur level above 0.05 percent by weight.
4. No. 2 Fuel oil (Heating Oil): A distillate fuel oil that has distillation temperatures of 204°C at the 10-percent recovery point and 338°C at the 90-percent recovery point and meets the specifications defined in ASTM Specification D 396. It is used in atomizing type burners for domestic heating or for moderate capacity commercial/industrial burner units.
No. 4 Fuel: A distillate fuel oil made by blending distillate fuel oil and residual fuel oil stocks. It conforms with ASTM Specification D 396 or Federal Specification VV-F-815C and is used extensively in industrial plants and in commercial burner installations that are not equipped with preheating facilities. It also includes No. 4 diesel fuel used for low- and medium-speed diesel engines and conforms to ASTM Specification D 975.

Distillation

Gasoline contains various hydrocarbons that boil at different temperatures. As a result, the gasoline boiling range can extend from 27°C to a maximum of 225°C. This is in contrast to water that boils only at 100°C at sea level.
The process of heating a liquid to its boiling point and condensing and collecting the vapors

Distillation Curve: The percentages of gasoline that evaporate at various temperatures. The distillation curve is an important indicator for fuel standards such as volatility (vaporization).

Distillation unit: See
Atmospheric distillation unit

Distilled water: Pure water that through distillation has had all other chemicals (salts, suspended solids, and organisms) removed. It is recommended for topping up batteries and radiators.

Distilling apparatus: Fluid-reclaiming device used to reclaim used refrigerants. Reclaiming is usually done by vaporizing and then recondensing refrigerant.

Distortion: A warpage, bendng, twisting, or change in form from the original shape.

Distribution: See
asymmetic power distribution
asymmetrical power distribution
constant power distribution
equal power distribution
load-controlled power distribution
load distribution calculation
load distribution
power distribution
static high-voltage distribution

Distribution calculation: See
load distribution calculation

Distribution channel: The path goods take as their title transfers from producer to consumer. The title transfer for consumer goods is usually accompanied by transfer of the physical goods, as well.

Distribution controls: Systems which help evenly and efficiently transfer the heating or cooling medium to the area where it is needed.

Distribution tube: See
distribution tubes.

Distribution tubes: Tubes used in the engine cooling area to guide and direct the flow of coolant to vital areas.

Distributor

Click image to supersize
Distributor

A unit in the ignition system designed to make and break the ignition primary circuit and to distribute the resultant high voltage to the proper cylinder at the correct time. The high voltage comes from the coil to the center terminal of the distributor cap and passes down the rotor. As the rotor turns, contact is made with each successive terminal on the circumference of the distributor cap. From there, the voltage goes into the spark plug wires and to the spark plug. Generally when your vehicle has its timing adjusted, it is the distributor that is adjusted. Also called "ignition distributor."
A distributor performs many of the same functions as wholesalers such as selling, physical distribution, credit, etc.; but is between the dealer and the wholesaler. Some industries use the term distributor instead of wholesaler.
A company primarily engaged in the sale and delivery of natural and/or supplemental gas directly to consumers through a system of mains.

Also See
breakerless distributor
fuel distributor
high-tension distributor
HT distributor
ignition distributor
shaft distributor
short-type distributor

Distributor baseplate: The fixed plate in the body of the distributor on which the contact breaker or triggering device is mounted, and through the centre of which the distributor shaft passes

Distributor body: The bowl-like part containing the distributor shaft with the rotor arm at its top end, and, in the conventional version, the centrifugal advance mechanism and the contact breaker

Distributor cam: The cam at the top of the distributor shaft with as many lobes as there are cylinders, acting on the heel of the contact breaker arm

Distributor cap: Distributor cap

An insulated cover containing a central terminal or tower with a series (one per cylinder) of terminals or towers that are evenly spaced in a circular pattern around the central terminal or tower, the secondary voltage travels to the central terminal or tower where it is then channelled to one of the outer terminals or towers by the rotor. The cap also keeps dirt and moisture out of the distributor.

Distributor clamp: See
distributor hold-down clamp

Distributor drive gear: A gear attached to the distributor shaft that meshes with a gear on the camshaft to cause the shaft in the distributor to turn.

Distributor hold-down clamp: A metal bracket at the base of the distributor that has a nut or bolt which can be loosened to allow the distributor to be moved on its shaft to readjust ignition timing or to open the points for gapping.

Distributor injection pump: A fuel injection pump using pistons which pressurizes fuel for injection in the proper cylinder based on the relative port position of the rotating shaft in the hydraulic head

Distributorless ignition system: (DIS or DLS) An electronic ignition system that does not have a conventional rotating distributor. Instead, it uses multi-spark ignition coils or one ignition coil for each spark plug.

Distributor pipe: A pipe or tube through which the fuel travels from the fuel distributor to the injection nozzle

Distributor rotor: A rotating part of the distributor which transfers high voltage to each spark plug. In a distributors with points, it is oblong-shaped; but in a distributors without points, it is usually a disc. Also called a "rotor" or "rotor arm."

Distributor shaft: Distributor shaft

The metal shaft inside the distributor that has a cam wheel which revolves with the shaft and forces the points to open. A spring causes the points to close. The distributor rotor is mounted on the top of this shaft.

Distributor tower: The terminals at the top of the distributor cap into which the spark plug wires fit. Also called "terminal tower"

Distributor weight: One of two flat pieces of metal found inside the distributor's centrifugal advance mechanism on the baseplate. They swing out as speed increases and consequently advances the timing of the spark.

Distributor wrench: A special tool used to tighten or loosen the distributor hold down clamp when installing or removing a distributor

District heating and cooling: Use of a central utility system designed to provide heating and cooling to large residential and industrial areas.

Dive: The action of the front of the vehicle to point downward (or dip) during braking. The opposite is squat.

Also See
anti-dive system
anti-lift
anti-squat system
anti-dive
brake dive
nose dive

Diversification: In today's market, especially in smaller centers, a dealership cannot make a profit on just one brand of vehicle -- especially foreign imports. Thus the dealership will diversify by having several brands (e.g., Mercedes-Benz, BMW, and Mazda). A car manufacturer diversifies by making several different kinds of vehicles (trucks, vans, luxury cars, family-size cars, commuter cars, compacts, convertibles, sports cars, etc.) in an attempt to reach every segment of the population. Some dealers or manufacturers may diversify by offering lawnmowers, boat motors, and motorcycles as well as automobiles (e.g., Honda) or even musical instruments (e.g., Yamaha).

Diversion: An alternative route which traffic has to follow due to closure of a stretch of road for repairs, etc. A detour.

Divert: To cause (air, a liquid, traffic, etc.) to follow a different course. For example, air is diverted to the air cleaner; traffic has been diverted around the accident site.

Diverter valve

A valve which adds an amount of air to the rich air-fuel mixture entering the intake manifold during deceleration.
Used in air injection system to channel airflow to either the exhaust manifold or oxidation catalyst under different operating conditions.

Also See
air gulp valve
air bypass valve

Divided propeller shaft: A propeller shaft, usually in long chassis rear-wheel drive vehicles, which is divided into two sections with a bearing and CV joint mounted on a chassis crossmember at the central point. Also called "divided propshaft"

Divided propshaft: A propeller shaft, usually in long chassis rear-wheel drive vehicles, which is divided into two sections with a bearing and CV joint mounted on a chassis crossmember at the central point. Also called "divided propeller shaft"

Divider: A measuring tool with two straight pointed arms used to mark off and transfer measurements, e.g., on sheet metal or other metal components.

Also See
spring divider

Divorced choke: Vacuum diaphragm is mounted on the carburetor, but the bimetal spring is mounted either on a pad on the intake manifold or in a heat well in the exhaust man. Choke lever is operated by a mechanical linkage rod from the bimetal spring. Also called a remote choke

DIY: An acronym for Do-it-yourself.

Also See
do-it-yourself market

DIY mechanic: A person, whether qualified or not, who does his own repairs on his own vehicle.