GLOSSARY TERMS

D

D
An abbreviation for drive; one of the forward gear positions in an automatic transmission.
D-1
The low forward-drive range of an automatic transmission.
D-2
The high, forward-drive range for an automatic transmission.
D-Cam
The pattern used for grinding pistons in a cam shape with a 0.012 inch (0.3 mm) difference between the thrust face and the pinhole side.
D-Jetronic
An early fuel-injection system by Bosch.
D-Port
An intake or exhaust port shaped like the letter D.
D-Ring
A control in a drag-racing car's cockpit used to deploy the chute at the end of the run.
DAC
An abbreviation for digital to analog converter.
Dam
The sealing provisions located between the radiator and condenser to ensure adequate ambient and ram air through both components.
Damage appraiser
A term often used for estimator.
Dampened Pressure Switch
An electrical pressure switch that opens the compressor clutch circuit when the low-side pressure is too low.
Dampener
A term often used incorrectly for damper.
Dampening Ball Joint
A term used for non-load-bearing ball joint.
Dampening Effect
The effect shocks have on reducing suspension-spring oscillations.
Damper
Friction or hydraulic shock absorbers or the equivalent electronic device.
A device that reduces or eliminates vibration or oscillation.
A balancer on the front of the crankshaft to reduce or eliminate harmonic vibration.
Damper Assembly
A device designed to decrease vibrations to the passenger compartment.
Dark Current
A small leakage current that flows through a photosensitive device in the absence of light.
Dash
A short term for dashboard.
A short race, usually about six laps.
Dash Components
Accessories, such as the air conditioner and/or heater, that are mounted on the firewall in the engine compartment.
Dash Control valve
Hand-operated valves located on the dash, such as parking-brake valves, tractor-protection valves, and differential locks.
Dash Series
A NASCAR race series for four-cylinder, subcompact cars.
Dashboard
The section immediately behind the windshield that houses the instruments, accessory controls, and glove box.
Dashpot
A device found on the carburetor that prevents a fast-closing throttle action.
Data Link
A device in a computer system that sends and receives digital signals.
Data Processor
A device that is capable of performing data operations, such as a microcomputer.
Datum Point
The starting point for measuring an object.
Daylight
To be ahead of a competitor by more than a car length in side-by-side racing, so daylight is visible between the two vehicles.
Daytona
The Daytona International Speedway.
Daytona International Speedway
A speedway in Daytona Beach, Florida. Home of the Daytona 500, Firecracker 400, and IMSA's 24-hour sport-car endurance race.
DB
A symbol for decibel.
DBC
An abbreviation for dual-bed catalytic.
DC
An abbreviation for direct current.
De Dion Axle
A drive system with a differential or transaxle attached to the frame and exposed, universal-jointed half-shafts driving the wheels with a separate dead axle connecting the wheels that holds them upright and supports the springs.
De-ice Switch
A switch used to control compressor operation to prevent evaporator freeze-up.
Dead Axle
A shaft, such as the rear axle on a front-wheel drive vehicle, that connects wheels to either side of a vehicle but does not provide driving power.
Dead Player
A vehicle part or assembly that is inoperable.
Dead Spot
The momentary loss of power in an engine while increasing its speed.
Dealership
A privately owned sales and service facility representing an automobile manufacturer.
Deburr
To remove sharp edges from a part.
Decarbonize
To remove carbon deposits. Also known as decarburize.
Decarburize
Same as decarbonize.
Decel Valve
A device that reduces exhaust emissions during vehicle deceleration by keeping rpm up and vacuum down.
Decelerate
To decrease speed.
Deceleration
A decrease in velocity or speed.
To allow the vehicle to coast to idle speed from a high speed.
Deceleration Valve
A device used with the dual-Diaphragm, vacuum-advance to advance engine timing under deceleration conditions.
Dechrome
To strip the vehicle of chrome for modification.
To remove the chrome prior to body repair and/or painting.
Decibel (dB)
A standard of measure for the relative loudness of a sound.
Deck
The flat, mating surfaces of an engine block and head.
The trunk of a passenger car.
To machine an engine block deck flat.
To dechrome the deck lid.
Deck Lid
The trunk door, or cover.
Deck Plate
A heavy metal plate that is bolted to an engine block during cylinder-honing operations.
Declutching Fan
An engine-cooling fan system, mounted on the water pump, having a temperature-sensitive device that governs or limits terminal speed.
Decoke
A British term for decarbonize.
Deep Cycling
A condition where a battery is completely discharged before it is recharged.
Deep Staging
A drag-racing technique where the driver uses minimum roll out to avoid breakout.
Deep Sump
An oil pan, used on some drag-race cars, that is deep enough to keep the oil away from the crankshaft at high rpm to slightly increase horsepower.
Deep-Dish Wheel
A wheel with an extremely positive offset.
Deep-Rolled Fillets
The transition radius between a journal and the cheeks of a crankshaft.
Deflection
An axial or radial movement away from the normal or standard axis of a part.
Deflection Angle
The angle at which oil is deflected inside a torque converter during operation; the greater the angle, the greater the torque applied to the output shaft.
Deflection Rate
The number of pounds required to compress a spring one inch (25.4 mm).
Defogger
That part of the heater system designed to clear the windshield of fog haze under certain conditions.
Defrost door
A small door within the duct system that diverts a portion of the delivery air to the windshield.
Defrost Switch
A thermostatic-type switch that senses evaporator temperature and turns the compressor off to prevent frosting or ice formation on the evaporator.
Defroster
That part of the heater system designed to clear heavy frost or light ice from the inside or outside of the windshield.
Defroster Door
A term often used for defrost door.
Deg
An abbreviation for degree.
Degreaser
A chemical that breaks oil and grease down.
Degreasing
Cleaning parts in a solvent to remove oil and grease.
Degree
Part of a circle; one degree is 1/360th of a circle.
Degreeing a Cam
Using instruments to determine the actual timing of valves opening and closing for a particular camshaft.
Dehumidify
To remove water vapor from the air.
Dehydrate
A process for dehumidifying.
Dehydrator
A machine used to dehydrate a system or component.
A term often used for drier.
Dehydrator Filter
A term used for filter drier.
Delco Eye
A type of built-in battery tester that provides an immediate visual indication of battery conditions.
Delta Connection
The interconnection of three electrical-equipment windings, such as an alternator, in a triangular fashion.
DEMA
An abbreviation for Diesel Engine Manufacturers Association.
Demagnetization
The process of removing magnetism from a magnetized substance.
Demagnetize
To reduce or remove the magnetism from an object.
Denatured Alcohol
Ethyl alcohol, used to clean brake systems; contains methanol, rendering it unfit for human consumption.
Department of Environmental Regulation (DER)
A department of the United States Environmental Protection Agency (EPA).
Department of Transportation (DOT)
The United States Department of Transportation, a federal agency charged with the regulation and control of the shipment of all hazardous materials.
Departure Angle
The maximum angle, in degrees, of a line running rearward and upward from the rear tire contact point to the lowest obstruction under the rear of the vehicle.
Depolarize
To remove or eliminate positive and negative poles from an item.
Deposited Metal
Any filler metal that may have been added during a welding process.
Depressed Park
The out-of-sight positioning, below the hood line, of windshield wiper blades of some wiper systems.
Depressurize
To release or remove pressure.
Depth of Fusion
The penetration that a weld fusion extends into the base metal, or previous bead, from the surface.
DER
An abbreviation for Department of Environmental Regulations.
Desiccant
A material, such as silica gel, that absorbs moisture from a gas or liquid.
A drying agent used in refrigeration systems to remove excess moisture.
Design Working Pressure
The maximum pressure under which a specific system or component is designed to work safely and without failing.
Desmodromic Valves
A valve system in which positive cam action, not spring action, is used to open and close the intake and exhaust valves.
Detent
A recess to hold the gear selector in the gear range selected.
A pin, stud, or lever which initiates or halts an action at a determined time or interval.
Detergent
A chemical, added to engine oil, that possesses the ability to clean by preventing the accumulation of deposits.
Detergent Dispersant
A chemical component in motor oil that loosens dirt and varnish in an engine.
Detergent Oil
An oil with a detergent additive.
Detonation
A phenomenon of internal combustion where the compressed air/fuel charge explodes violently instead of burning smoothly, usually due to the creation of a second flame front in the combustion chamber, away from the spark plug.
Detonation Sensor
A device, mounted on an engine block, cylinder head, or intake manifold, that generates and sends a small voltage signal to the ECU, to retard timing, when encountering the vibration frequency associated with detonation.
Detonation-Detection Sensor
A term often used for detonation sensor.
Detroit Locker
A specific brand of locking rear-end differential.
Deuce
A 1932 Ford.
A two-barrel carburetor.
A 1962 through 1967 Chevrolet.
Deuce and a Half
A truck having a nominal payload capacity of 2-1/2 tons.
Deuce and a Quarter
The Buick Electra 225, particularly the 225-inch-long 1959 model.
Deutsche Institut für Normung (DIN)
A German standards authority.
Dexron II
A petroleum-based automatic transmission fluid developed by General Motors.
DG
An abbreviation for double-groove valve stem.
Dia
An abbreviation for diameter.
Diagnosis
A standard procedure that is followed to locate and identify the cause of a malfunction.
Diagnostician
A person who determines the cause of problems when given all the signs and symptoms.
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 Cross Check
In preparation for oval-track racing, the measure of weight distribution between the right-front and left-rear wheels and between the left-front and right-rear wheels.
Dial
An instrument with an analog-gauge indicator.
Dial In
To set the Christmas tree for drag racing events, with the interval between starting times for vehicles with different indexes.
To set up a car with the right combination for maximum performance for any particular racing condition.
Dial Under
A practice allowed under NASCAR rules in handicap eliminations for Stock and Super Stock classes where the breakout rule is in effect.
Diameter
The cross-section measurement of a round or circular object.
Diaphragm
A flexible membrane in a speaker or microphone where electrical signals are converted to sound vibrations and vice versa.
The flexible membrane found in a temperature- or pressure-control device that seals in an inert fluid from the atmosphere while allowing a mechanical movement.
Diaphragm Clutch
A clutch having a shallow, cone-shaped spring disc to provide pressure to the plate.
Diaphragm Spring
A spring shaped like a disk with tapered fingers pointed inward.
A spring shaped like a wavy disk.
Diaphragm-Spring Clutch
A clutch in which a Diaphragm spring applies pressure against the friction disk.
Dice
A tight contest between two cars on an oval track or road course generally battling for a specific position.
Dichlorodifluoromethane
The proper chemical name for Refrigerant-12.
Die Out
To stall or stop running.
Dielectric
An insulator.
A term referring to the insulation between the plates of a capacitor.
Dielectric Strength
The ability of an insulator to insulate; to resist carrying current.
Diesel Cycle
An engine operating cycle where the air is compressed and the fuel is injected at the end of the compression stroke, causing ignition.
Diesel Engine
A compression-ignition engine.
Diesel Engine Manufacturers Association (DEMA)
A professional association of diesel-engine manufacturers.
Dieseling
A condition in which a carbureted engine continues to run after the ignition is shut off.
Diff
An abbreviation for differential.
Differential
The section of the rear-axle assembly that provides three functions it allows the wheels to revolve at different speeds during turns, provides the final gear reduction, and changes the angle of drive 90 degrees.
Differential Action
An operational situation where one driving wheel can rotate at a slower speed than the opposite driving wheel.
Differential Assembly
The mechanism that relates to front- or rear-driving axles that permits unequal travel distances and speeds between the vehicle's driving wheels.
Differential Case
The housing of the differential that contains the side and pinion gears and the pinion shaft, and also serves as a mounting place for the ring gear.
Differential Drive Gear
A large, circular helical gear that is driven by the transaxle pinion gear and shaft and that drives the differential assembly.
Differential Housing
Also known as rear-axle housing. A cast iron assembly that houses the differential unit and the drive axles.
Differential Lock
A toggle or push-pull type air switch that locks together the rear axles of a tractor so they pull as one for off-the-road operation.
Differential Pinion Gears
Small, beveled gears located on the differential pinion shaft.
Differential Pinion Shaft
A short shaft locked to the differential case. This shaft supports the differential pinion gears.
Differential Pressure Valve
A device that maintains a constant pressure to fuel injectors.
Differential Side Gear
The gears that are internally splined to the axle shafts, which are driven by the pinion gears.
Dig Out
To accelerate suddenly, as in the start of a race.
Digger
A dragster.
Digital
Relating to the technology of computers and data communications where all information is encoded as bits of 1's or 0's that represent ON or OFF states.
A numerical readout.
Digital Computer
A device that manipulates digital data and performs arithmetic and logic operations on such data.
Digital Electronic Fuel Injection
An early Cadillac electronic fuel-injection system.
Digital Instrument
A display that indicates an activity, such as rpm, mph, voltage, or fuel supply, with an electronic readout; used in most Indy cars, though some drivers still prefer analog instruments.
Digital Read Out (DRO)
A method of electronically reading conditions as opposed to an analog readout.
Digital Speech
Recorded speech broken into tiny units of sound, each having characteristics such as pitch and loudness that can be represented by numbers, becoming the digital code for speech.
Digital-to-Analog Converter
A device, generally electronic, used to convert discrete digital numbers to continuous analog signals.
Digs
The drag races.
Diluent
A liquid that extends a solution but definitely acts to weaken the solvent power of the active solution.
Dilution
To make thinner or weaker. Oil is diluted by the unintentional addition of fuel and water droplets.
Dimmer Switch
A switch that allows the driver to select either high- or low-beam operation of the headlights, and to switch between the two.
Dimple
The process of turning a hole under or down to allow the installation of a fastener.
Dimpling
The distortion of an oil-pan rail around the bolt hole.
DIN
An abbreviation for Deutsches Institut für Normung.
Ding
A small dent.
Dip Stick
A thin, steel strip of metal used to measure the fluid level or quantity in the engine, transmission, or compressor.
Dipper
A small, metal scoop at the bottom of a connecting rod to scoop up oil from the pan to lubricate the bearing.
Dipper Trough
A trough aligned under the connecting rod that is fitted with the dipper.
Direct Battery Power
Power available to a circuit in the automobile directly from the battery, without an intermediate switch.
Direct Current
The current produced by a battery.
Direct Drive
A transmission mode in which the driveshaft and engine crankshaft are at the same speed.
Direct Ignition System
An ignition system where impulses are sent directly to the spark plugs by a modulator.
Direct Injection
A type of fuel-injection system that injects fuel directly into the cylinders.
Direct-Acting Shock Absorber
A double-action design controlling up and down suspension travel; it is mounted directly between the frame of the vehicle and the control arm or axle.
Direct-Acting Thermostatic Air Cleaner
A component of heated air-intake systems that uses a thermostatic bulb connected to a rod to operate a flapper valve in the air-cleaner snorkel.
Direct-Bonded Bearing
A bearing that is formed by pouring molten babbitt directly into the bearing housing and machining the cooled metal to the desired diameter.
Direct-Clutch Solenoid
A solenoid that directs fluid flow to engage the direct clutch.
Directional Signals
Lights at either side of both the front and rear of the vehicle that flash to indicate an intended turn.
Directional Tire
A tire having a tread pattern that must be mounted facing forward.
Dirt Dobber
A circle-track race driver that prefers a dirt track over an asphalt track.
Dirt Tracking
Driving on an asphalt track as if it were a dirt track.
Disable
To remove or inhibit normal capability.
A command that prevents further operation of a peripheral device.
Disassemble
To take apart.
Disc
An abbreviation for discount.
A variant of disk.
Disc Brake
A type of brake that provides a means of slowing or stopping a vehicle using hydraulic pressure to apply pads against a rotor.
Disc Minimum Thickness
The least thickness, usually stamped or cast into the disc, to which a brake disc can be machined or worn before it becomes unsafe.
Disc-Brake Fluid
A special fluid having a high boiling point, about 500°F (260°C). If exposed to air, it will attract moisture and be unsafe for use.
Disc-Brake Pad
An assembly consisting of friction material and its steel backing.
Discharge
Releasing some, or all, refrigerant from a system by opening a valve to permit the refrigerant to escape slowly into a recovery system.
To purge air from a sealed system.
Discharge Air
Conditioned air as it passes through the outlets and enters the passenger compartment.
Discharge Line
The fluid line that connects the compressor outlet to the condenser inlet.
Discharge Pressure
The high-side pressure of the refrigerant as it is being discharged from the compressor. Also known as high-side pressure.
Discharge Pressure Switch
A term used for compressor-discharge pressure switch.
Discharge Side
That portion of the refrigeration system under high pressure, extending from the compressor outlet to the metering-device inlet.
Discharge Valve
A term used for high-side service valve.
Disconnect
A switching device for disconnecting an electrical circuit or load from the power supply.
Discrete Components
An electrical component, such as a capacitor, that has been fabricated prior to its installation.
Discrete Device
An individual electrical component, such as a resistor.
Dished Piston
A piston having a depression in the crown.
Disk
A magnetic device for storing information and programs accessible by a computer.
The rotor, a revolving piece of metal, against which shoes are applied to provide a braking action.
A two-dimensional figure defined by all points enclosed by a circle's diameter.
Often referred to as disc.
Disk Drive
A device that stores, reads, or retrieves data from a magnetic disk and copies it into the computer's memory for use.
Disk Runout
The amount that a brake disk wobbles during rotation.
Disk-Operating System
An operating system in which the programs are stored on magnetic disks that keep track of, save, and retrieve files; allocate storage space and manage other control functions.
Dispersant
A chemical added to oil that prevents impurities from clinging together and forming lumps that could clog the lubrication system galleys.
Displacement
The volume within an engine's cylinders, usually expressed in cubic centimeters (cc).
Displacement Current
An expression for the effective current flow across a capacitor.
Display Terminal
An output device, such as a CRT, that produces a visual representation of graphic data.
Disposable Cylinder
A container for the one-time use of packaging, transporting, and dispensing of a fluid, such as refrigerant. It is a violation of Federal Law to refill these cylinders, commonly referred to as DOT-39s.
Disqualified
To render unfit.
To be deprived of a right or privilege.
Dist
An abbreviation for distributor.
Distillation Endpoint
The temperature at which a fuel is completely vaporized.
Distortion
Inaccuracies in size and shape, as in an out-of-round cylinder.
An unwanted change in purity of sound, as caused by a weak signal.
A term used for tread distortion.
Distributor
A jobber; one who buys from a manufacturer and sells to a wholesaler.
A device used to direct electrical current to spark plugs.
A device used to direct fuel to injectors.
Distributor Advance
A term used for centrifugal advance, ignition advance, or vacuum advance.
Distributor Cam
The four-, six-, or eight-sided lobe at the top end of the distributor shaft that rotates to cause the contact points to open and close.
Distributor Cap
A cover for the conventional ignition-system distributor, having a central terminal that receives secondary voltage from the coil and four, six, or eight peripheral terminals to send this voltage to the spark plugs.
Distributor Housing
A metal part that contains or provides a mounting for distributor components in a conventional ignition system.
Distributor Ignition
An ignition system that relies on a conventional distributor for proper operation.
Distributor Pipe
A pipe to convey fuel from the fuel distributor to the injector.
Distributor Plate
The plate inside a distributor that is fastened to the housing and does not move.
Distributor Rail
A term used for distributor pipe.
Distributor Timing
A term used for ignition timing.
Distributor Vacuum Advance
A term used for vacuum advance.
Distributor Vacuum-Advance Control Valve
A term often used for deceleration valve.
Distributorless Ignition
A term used for distributorless ignition system.
Distributorless Ignition System
An ignition system that relies on a computer to distribute the electrical spark to the proper spark plug.
Div
An abbreviation for division.
Dive
The tendency of the front of a vehicle to press down on the front springs during heavy braking.
Divergent Nozzle End
An exhaust-pipe nozzle end that expands from the pipe inlet to the end.
Divergent-Convergent Nozzle end
An exhaust-pipe nozzle that is expanded then reduced in size at the end.
Diverter Valve
A vacuum-operated valve in an air-injection system that directs air-pump output to the atmosphere during high-vacuum deceleration to eliminate backfiring.
Division
A branch or department of an organization.
The mathematic operation to determine how many of one number is contained in another; for example, how many 10s are in 100.
DIY
An abbreviation for do-it-yourself.
DIYer
An abbreviation for a do-it-yourselfer.
Dizzy
Slang for distributor.
DNF
An abbreviation for did not finish.
Do-it-yourself (DIY)
To repair one's vehicle.
Do-it-yourselfer (DIYer)
One known to repair their own vehicles.
Dog
A poor performing vehicle.
To follow another car very closely in oval-track racing.
A pin or stub used to mate and/or drive a gear or assembly.
Dog Clutch
A simple splined clutch that cannot be slipped; generally found in dirt-track cars without transmissions.
The mating collars, flanges, or lugs that can be moved as desired to engage or disengage similar collars, flanges, or lugs in order to transmit rotary motion.
Dog House
The housing over an engine or transmission.
The front fenders, grille, and hood assembly of a vehicle.
Dog Leg
A sharp, angular turn.
Dog Tracking
Off-center tracking of rear wheels as related to the front wheels.
DOHC
An abbreviation for dual overhead camshaft.
Dolly
To shape or form metal.
DOM Tubing
An abbreviation for drawn-over mandrel tubing, a type of seamless tubing with precise and consistent inside and outside dimensions, used for race-car chassis construction.
Domed Piston
A piston having a raised crown.
Donuts
A 360-degree tire burnout.
Tires, especially big racing slicks.
Dooley
A Chevrolet pick-up truck with dual rear wheels; generally a term given to any dual-wheel vehicle.
Doorslammer
A full-bodied drag car with functioning doors.
Doosy
A variation of doozie.
Doozie
Short for Duesenberg, considered the greatest racing car ever built in the United States.
Anything, such as a car, that is truly fine or outstanding.
Doped Solder
Solder containing a small amount of an added element to ensure retention of one or more characteristics of the materials on which it is used.
DOT
An abbreviation for Department of Transportation.
DOT 39
Trade jargon for a disposable refrigerant cylinder. Disposable cylinders should never be refilled or used as compressed air tanks.
Double A-Arm
A suspension system using two A-arms or A-frames to connect the chassis to the wheel spindle.
Double Cardian Joint
A near-constant-velocity universal joint consisting of two Cardian joints connected by a coupling yoke.
Double Century
Two-hundred miles per hour.
Double Clutch
A driving technique to minimize gear clash when shifting gears with a manual transmission.
Double Filament Lamp
A lamp designed for more than one function; used in the stoplight, tail light, and the turn-signal circuits combined.
Double Flare
A flare on the end of tubing, made by folding it over to form a double face.
Double Pivot Control Arm
A term used for control arm.
Double Pole Double Throw (DPDT)
A term used to identify a switch configuration having six terminals that connects one pair to either of the other two pairs of terminals.
Double Pole Single Throw (DPST)
A term used to identify a switch configuration having four terminals that connect or disconnect two pairs of terminals simultaneously.
Double Ton
Two-hundred miles per hour.
Double Wishbone
A term used for double A-arm.
Double Wrap
A flexible type of brake band designed with two segments that provide flexibility, which increases self-energizing action.
Double-A Frame
A term used for double-A arm.
Double-Acting Shock Absorber
A shock that provides a dampening effect on both compression and rebound.
Double-Groove Valve Stem
A valve stem having two keeper grooves.
Double-Hump Heads
A term used for camel-hump heads.
Double-J Rim
The double-J shaped safety locks on a rim, used to hold the inner and outer tire beads securely.
Double-Reduction Differential
A differential that contains extra gears to provide additional gear reduction.
Dowel
A pin inserted in an object or part to aid in the alignment of another object or part.
Dowel Pin
A round, solid, or hollow pin used to align two or more parts.
Downdraft Carburetor
A carburetor having a downward airflow.
Downflow Radiator
A radiator in which the coolant flow is from the top tank to the bottom tank.
Downforce
The downward force of air on a speeding vehicle.
Downshift
The automatic shift from a high gear ratio to a low gear ratio.
Downstream Blower
A blower arranged in the duct system so as to pull air through the heater and/or air-conditioner core(s).
Downtime
The time a system or machine is not available for use, due to failure or routine maintenance.
Time lost due to lack of service orders.
Downward Spring-and-Wheel Action
A term used for rebound travel.
DPDT
An abbreviation for double pole double throw.
DPST
An abbreviation for double pole single throw.
DQ
An abbreviation for disqualified.
Draft
To follow another vehicle close enough to take advantage of the slipstream or partial vacuum created behind it at very high speeds.
Draft Tube
A vent to release engine-crankcase vapors.
Drafting
The technique of following another vehicle closely to save fuel.
Drag
A performance term for a quarter-mile race from a standing start, against time or another car.
An acceleration contest between two vehicles.
The resistance of air against an object trying to pass through it.
Drag Coefficient
A term used for coefficient of drag.
Drag Link
The steering component that connects the Pitman arm to the steering arm.
Drag Racing
An acceleration contest between two vehicles.
Drag Strip
A standard racing strip 60 feet (18.3 meters) wide by 4,000 feet (1,219 meters) long, where eighth- or quarter-mile-competition events occur.
Dragster
A vehicle used for drag racing.
Drawbar
That part of a converter dolly that allows the fifth wheel to be repositioned on the frame.
Drawbar Capacity
The maximum, horizontal pulling force that can be safely applied to a coupling device.
Drawn-Over Mandrel Tubing
A type of seamless tubing with an accurate and precise inside and outside dimension; used in the construction of a race-car chassis.
Dressing
A term used for belt dressing.
Drier
A tubular device containing desiccant, usually placed in the liquid line to absorb moisture in an air-conditioning system.
A catalyst added to paint to speed the time required for curing.
Drift
A controlled slide through a turn involving all four wheels.
Drift Pin
A round, tapered, steel pin used to bring plates that are to be bolted or riveted into alignment to permit placing bolts or rivets easily.
Drilled Oil passage
Holes drilled in various parts of the engine for pressurized oil to flow through.
Drip Pan
A shallow pan under the evaporator core to catch the condensation that will be ejected by a drain hose fastened to the drip pan and extending to the outside.
Drive Axle
An axle or axle shaft that transmits power to the drive wheels.
Drive Belt
Flexible belt or belts used to connect a drive pulley on the crankshaft to the coolant pump and accessories. Two basic types of drive belts are the serpentine or multiple-ribbed belt and the V-belt.
Drive By Wire
To use an electronic throttle control rather than mechanical linkage.
Drive Coil
A hollow field coil in a positive engaged starter that is used to attract the moveable pole shoe.
Drive Fit
A term used for interface fit.
Drive Gear
In a combination of two operating gears, the first is the drive gear and the other is the driven gear.
Drive Line
Assembly of various parts such as the driveshaft, universal joints, and connecting yokes that transmit torque from the transmission to the differential.
Drive Pinion Gear
One of the two main driving gears to multiply engine torque located within the transaxle or rear-driving axle housing.
Drive Shaft
An assembly of one or two universal joints connected to a shaft or tube used to transmit power from the transmission to the differential.
Drive-Line torque
The transfer of torque between the transmission and the driving axle assembly.
Drive-Line Windup
A reaction that takes place as a result of the transfer of engine torque through the rear-wheel drive-line.
Driveability
The general operation of a vehicle, rated from good to poor, based on the characteristics of the average driver.
Driven Disk
The friction disk of a clutch.
Driven Gear
The gear that receives the driving action from the drive gear.
Driven Pinion
A rotating shaft in the differential that transmits torque to another gear.
Driven Plate
The friction plate in a clutch assembly.
Driver
The operator of a vehicle.
A car for everyday use.
Driver-Reaction Distance
The distance traveled between the point at which the driver perceives a need to brake and the actual start of brake application.
Drivetrain
All of the components required to deliver engine power to the road surface.
Driving Axle
An axle capable of transmitting power by way of a differential or other transmission arrangement. Also a term used for drive axle.
Driving Lamps
Auxiliary lights to provide additional illumination for high-speed driving.
Driving Lights
A term used for driving lamps.
DRO
An abbreviation for digital read out.
Drop
To lower a structural part of a vehicle.
Drop Head Coupe
A British term for a two-door convertible.
Drop The Hammer
To engage the clutch and depress the accelerator suddenly.
To suddenly depress the accelerator to the floorboard.
Drop Through
The undesirable sagging or surface irregularity encountered when brazing or welding; caused by overheating with rapid diffusion between the filler metal and the base metal.
Drop-Center Rim
A wheel that has a smaller diameter center section, to facilitate tire replacement, designed to prevent the tubeless tire from rolling off the rim when the tire blows out.
Drop-Center Safety Rim
A wheel rim with a low center area and raised flanges designed to prevent the tire from accidentally coming off the rim.
Drop-Center Wheel
A conventional wheel that has a space in the center for one bead to fit into while the other bead is being lifted over the rim flange.
Drop-Throttle Oversteer
A term used for lift-throttle oversteer.
Dropped Axle
A lowered beam axle used on older Fords to dump the front end.
Druid
A term used by a dissatisfied contestant, who has problems with the rules, when referring to a race official.
Drum
The part of a brake that rotates with the axle hub and that the brake shoes press against to slow or stop the vehicle.
Drum Armature
A generator or motor armature having its coils wound longitudinally or parallel to its axis.
Drum Brake
A type of brake in which stopping friction is created by shoes pressing against the inside of the rotating drum.
Drum Maximum Diameter
The largest diameter, generally 0.060 inch (1.5 mm) over original, to which a brake drum can be machined or worn before it is considered unsafe.
Drum-Brake Fade
The loss of braking efficiency due to excessive heat.
Dry
The process of changing from a liquid to a solid, as in paint.
The process of evaporation, as in water.
Dry Deck
A condition in which the piston crown is at the level of the block deck.
Dry Friction
The friction between two dry solids.
Dry Fuel
A fuel with an additive to prevent water from collecting and freezing in the fuel system.
Dry Gas
Same as dry fuel.
Dry-Charged Battery
A battery that is filled with electrolyte only when put into service.
Dry-Disk Clutch
A clutch in which the friction faces of the friction disk are dry.
Dry-Film Lubricant
A petroleum-based chemical used to lubricate operating parts during assembly, prior to engine start up, to provide lubrication until oil is circulated after start up.
Drying Agent
A term used for desiccant.
Dual Camshaft
A type of engine that has two camshafts for opening and closing additional valves.
Dual Exhaust
An exhaust system used on V-type engines with a separate muffler, exhaust, and tail pipe for each cylinder bank.
Dual Master Cylinder
A master cylinder, associated with a dual-brake system, having two sections for displacing fluid under pressure; generally one section for front brakes and one section for rear brakes or, in some applications, one for left brakes and the other for right brakes.
Dual Overhead Camshaft
Two cams in a single-cylinder head.
Dual Quads
Two four-barrel carburetors.
Dual-Area Diaphragm
An automatic transmission shift control that receives its vacuum signal from the intake manifold and the EGR port.
Dual-Bed Catalytic
A term used for dual-bed catalytic converter.
Dual-Bed Catalytic Converter
A catalytic converter that passes different gases through an upper or front chamber coated with platinum and rhodium and a lower or back chamber coated with platinum and palladium.
Dual-Bed Converter
A term used for dual-bed catalytic converter.
Dual-Brake System
A brake system that uses two hydraulic circuits; should one fail, the other remains operational.
Dual-Diaphragm Advance
A vacuum-advance mechanism with two Diaphragms; one for normal ignition timing and the other to retard the spark during idling and part-throttle operation.
Dual-Diaphragm Distributor
A distributor incorporating a dual-Diaphragm advance.
Dual-Fuel Engine
An engine designed to run on two separate fuels, such as gasoline or propane.
An engine designed to run on two fuels simultaneously, such as gasoline, alcohol, or a combination of the two.
Dual-Idler Gear Drive
A timing-gear system having two idler gears for the crankshaft to drive the camshaft.
Dual-Ignition System
An ignition system having two coils and two distributors, with two spark plugs for each cylinder.
Dual-Plane Crankshaft
A crankshaft with two throws in two planes at right angles.
Dual-Plane Manifold
An intake manifold with two air cavities to provide air/fuel mixture to the cylinders.
Dual-Point System
An ignition system with two sets of points in the distributor.
A system that controls spark timing by electro-mechanical selection of separate advance and retard points.
Duallie
A Dodge pick-up truck with dual wheels; popular reference for any dual-wheel vehicle.
Duals
A term generally referring to two exhaust systems; two of anything, wheels, for example.
Ducktail
An upswept rear end, often with a spoiler.
Duct
A tube or passage used to provide a means to transfer air or liquid from one point or place to another.
Duct Tape
A heavy duty, fiber-backed tape used for emergency repairs to body parts, in all forms of racing.
Ductility
The property of a material that permits it to be worked by drawing or stretching without rupture.
Duesie
Anything truly fine or outstanding.
Short for Duesenberg, touted by many to be the finest race car ever built. Also, doozie.
Dummy
A mannequin, such as used in crash tests.
Dummy Load
An electrical test procedure to simulate actual operating conditions.
Dummy Shaft
A shaft used as an aid in the assembly or disassembly of a parts group.
Dump
To lower the front end.
To defeat a competitor in a drag race.
To damage or destroy a component, such as a transmission.
Dump Station
A facility where RV's and others clean their holding tanks.
Dump Tubes
Straight through exhaust headers.
Dumped and Tubbed
A vehicle that has been lowered in the front and fitted with oversize wheel wells.
Dune Buggy
A small, light-weight, off-road vehicle with little or no body work.
Duo-Servo
A drum brake design with increased stopping power due to the servo or self-energizing effect of the brake.
Dura Spark Ignition
An ignition system developed by Ford.
Durability
The quality of being useful, generally referring to the life of a catalyst or emission-control system.
Duration
The time, in crankshaft degrees, that a camshaft holds an exhaust or intake valve open.
Dust
To overtake or defeat a competitor in a race.
Dust Off
A term often used for dust.
Dust Shield
The upper portion of a shock absorber that surrounds the lower twin-tube unit.
A covering that protects an assembly from the elements.
Dutched
A paint job finished with elaborate striping or flame painting.
Duty Cycle
The percentage of time that a power source, or one of its accessories, can be operated at rated output, without overheating.
Duty Solenoid
A solenoid on a feedback carburetor that cycles many times per second to control a metering rod, and therefore, the air/fuel mixture.
Dwell
The degree of distributor-shaft rotation while the ignition breaker points are closed.
Dwell Angle
A term used for dwell.
Dye-Penetrant Testing
A non-destructive, inexpensive method of testing metal for cracks.
Dyer Drive
A type of starter-motor drive used in heavy-duty applications that provides mechanical meshing means and automatic demeshing.
Dykes Ring
A compression piston ring having an L cross-sectional shape that provides sealing against the cylinder walls.
Dykum Blue
A blue dye used to color metal.
Dynamically Balanced
A term that often refers to a wheel and tire being balanced while spinning.
In general terms, the balance of any object when it is in motion.
Dynamo
An electric DC-current generator.
Dynamometer
A machine on which a vehicle may be driven, simulating actual driving conditions for emissions and diagnostic purposes.
Dyno
Short for dynamometer.
Dytel
A trade name for a red dye found in some CFC refrigerants.
Dzus Fastener
A screw-like fastener that may be removed or installed with a quarter turn, ideal for race-car body panels that may have to be replaced quickly.
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