DICTIONARY OF AUTOMOTIVE TERMS - "Du"

Dual:

1. A combination of two nearly identical parts (e.g., a truck with dual tires has two tires at each end of the axle).
2. In Britain, dual is a verb meaning to twin a highway or railroad.

Dual-acting:

See:
double-acting

Dual axles:

See:
tandem axles

Dual bead tire:

Heavy service and large truck tires using two or more sets of bead wires in each bead rather than one.

Dual-bed catalytic converter:

A catalytic converter which combines two converters (with different catalysts) in a single housing

Dual brake:

See:
dual brakes.

Dual brakes:

A brake system that uses a tandem or dual master cylinder to provide separate brake system for both front and rear of vehicle. In the event of a loss of hydraulic fluid, one system may still work because it is independent of the other system. Often the front left brake is linked with the right rear brake. Likewise the right front brake is linked with the left rear brake. Some cars like the Rolls-Royce, link the two front brakes with the right rear brake, and the two front brakes with the left rear brake. Also called "dual-circuit braking system."

Dual brake system:

A brake system that uses two hydraulic circuits. Should one circuit fail, the other remains operational

Dual braking system:

See:
dual brakes.

Dual breaker points:

A distributor, using two sets of breaker points, to increase the cam angle so that at high engine speeds, sufficient spark will be produced to fire the plugs.

Dual carbs:

Two carburetors on the same engine.

Dual carburetors:

Two carburetors on the same engine.

Dual carriageway:

A British term for a divided highway (i.e., a road that has four lanes -- two in one direction and two in the other -- separated by a median).

Dual-circuit braking system:

A brake hydraulic system composed of two separate hydraulic circuits.
See:
dual brakes

Dual controls:

A second set of controls for use by a driving instructor when teaching someone to drive

Dual-crown fork:

A type of bicycle suspension fork that resembles a motorcycle fork due to crowns above and below the head tube, which increase stiffness

Dual drive:

1. Tandem axles, both powered directly by the engine.
2. Colloquial term for twin screw.

Dual exhaust system:

See:
twin exhausts

Dual fuel engine:

An engine equipped to operate on two different fuels such as gasoline and LP-Gas

Dual Ghia:

A vehicle brand of which the 1956-58 models are milestone cars.

Dualie:

See Dual-suspension bike

Dual ignition system:

See:
twin ignition system

Dual-line braking system:

A braking system in which a towing vehicle and trailer are connected by two or more brake lines

Dual master cylinder:

Type of master cylinder associated with dual brake systems

Dual mounting:

Two tires mounted together on each side of an axle of several types: cast spoke type, disc wheel type (held on by double cap nuts or inner cap nuts and outer cap nuts), Chevrolet type, and motor wheel type

Dual overhead cam engine:

See:
double overhead cam engine.

Dual-piston engine:

See:
twin-piston engine

Dual-piston master cylinder:

See:
tandem master cylinder

Dual-power brake system:

A system that uses both a vacuum booster and a hydraulic booster to increase brake application.

Dual-purpose motorcycle:

Street-legal motorcycles with varying degrees of off-road capabilities. Also called dual-sport

Dual purpose ship:

Specially designed ship for carrying different types of cargoes such as ore and/or oil.

Dual-range gearbox:

See:
dual-range transmission

Dual-range transmission:

A transmission in a four-wheel drive vehicle and some motorcycles with two sets of ratios, usually a higher set for road use and a lower set for off-road use.

Dual reduction axle:

A drive axle construction with two sets of pinions and gears, either of which can be used

Duals:

1. Two sets of exhaust pipes and mufflers -- one for each bank of cylinders.
2. Two tires on each end of an axle.

Also See:
between duals
kissing between duals

Dual spacing:

A measurement in inches (or millimeters) from the center of the tread of one tire, to the center tread of the other tire in dual, which provides clearance between duals for air circulation.

Dual sport:

Street-legal motorcycles with varying degrees of off-road capabilities. Also called dual-purpose motorcycles

Dual-suspension bike:

A bicycle with front and rear suspension; also known as a "dualie"

Dual-tone horn:

See:
two-tone horn

Dubonnet suspension:

An independent front suspension and steering arrangement used in the 1930s and '40s, in which the axle beam is rigidly attached to the vehicle frame, and the kingpins carry sprung steering and suspension arms, from which the wheels are mounted on stub axles

Duct:

A tube or channel through which air, gas, or liquid is conducted, conveyed, or moved.
Also See:
air duct
NACA duct
oil duct

Ductile:

Metal which can be bent, hammered, or drawn out into wire or sheet without fracturing

Ductility:

The ability of a material to undergo stretching or bending without fracturing

Duesenberg:

A vehicle brand of which the 1925-1948 models are classic cars.
Click image for books on Duesenberg

Duesy:

Expression to indicate quality, as "It's a duesy." The word is derived from the high quality Duesenberg automobiles.

Dull:

1. A finish that is not shiny.
2. A blade, saw, or drill bit that is not sharp.
   

Also see:
go dull

Dumbirons:

The front extensions of the side members of a chassis frarne in older designs, to which were fitted the front ends of the leaf springs carrying the front axle.

Dummy:

A stuffed figure made to look like a human being, used, for instance, when crash testing cars. Also called a crash test dummy.
Also See:
crash test dummy
side impact dummy

Dummy lights:

1. Exterior lights which do not work, but may enhance the appearance of a vehicle.
2. The "idiot lights" that indicate a condition, but does not give details as a gauge would do, e.g., an oil light that indicates low pressure. By the time it comes on, you may have damaged your engine.

Dump:

See:
end dump

Dump body:

A large truck's metal body which is generally hinged at rear and dumped by hydraulic means. The size is generally given in cubic yard water level capacity.

Dumps:

See:
bottom dumps

Dump truck:

1. A large truck with a bed designed to be tilted at its front to unload its contents usually through a gate in the rear.
2. In Britain it is a small truck with a tipping container in front of the driver, used in construction, like a front-end loader

Dump valve:

A valve for relieving pressure, such as that between the turbocharger and the carburetor in some systems

Dunnage:

Cushioning material placed among cargo to prevent their motion

Duo-servo:

A drum brake that has servo action in both the forward and reverse directions.

Duo-servo brake:

A servo brake with one double-end wheel cylinder and two linked self-energizing brake shoes

Duo-servo drum brake:

A type of self-energizing drum brake that has servo action in both forward and reverse

Duplex:

Double, having two parts. Applies to motorcycle frames with two downtubes, and chains with double rows of rollers

Duplex chain:

A chain with two rows of rollers, used especially for timing chains.
Also See:
simplex chain
triplex chain

DuPont:

A vehicle brand of which the 1925-1948 models are classic cars.

Durability:

1. The ability of a component or entire vehicle to last a long time.
2. The expected lifespan of a paint film

Durable:

The ability of something to be serviceable for a long time before being replaced

Duraspark system:

Ford electronic ignitions system

Duration:

The length of time that an action is allowed to operate or that something is supposed to last.
Also See:
spark duration
valve duration

Durometer:

A device to indicate the hardness of rubber.

Duryea:

See:
Stevens Duryea

Dust boot:

1. A covering (often shaped like an accordian) usually made of rubber or plastic to cover over a shaft, CV joint, etc.
2. A rubber diaphragm-like seal that fits over the end of a hydraulic component and around a pushrod or end of a piston, not used for sealing fluid in but keeping dust out
3. Flexible rubber or plastic covers that seal out foreign matter from brake components

Dust cap:

1. A metal or plastic covering that fits into a hub shell to keep contaminants out of hub bearings.
2. A metal or plastic end cover for a spindle in a pedal or a cotterless crankset.

Dust cover:

1. A soft, flexible valve cap to protect the valve assembly from dust while in shipment and storage. It is not capable of sealing the air pressure and should not be used in service.
2. Small plugs made of rubber or metal, used to cover the access holes in backing plates and brake drums.

Dust-free paint:

A condition of paint which has hardened beyond being tacky so that any air-borne dust particles will not be imbedded in the paint.

Dust sheet:

A sheet for covering a car when in a garage and not in use.
Also See:
car cover

Dust shield:

Sheet metal disc or plate placed on the brake assembly to keep debris from brake assembly. Also called "splash shield."

Duties:

See:
customs duties

Duty:

See:
heavy-duty
light-duty

Duty cycle:

1. The relationship between the operating and rest time. An electrical motor which can continue to operate within the temperature limits of its insulation system after it has reached normal operating (equilibrium) temperature is considered to have a continuous duty (CONT) rating. One which never reaches equilibrium temperature but is permitted to cool down between operations is operating under intemittent duty (INT) conditions
2. Many solenoid-operated metering devices cycle on and off. The duty cycle is a measurement of the amount of time a device is energized, or turned on, expressed as a percentage of the complete on-off cycle of that device, in other words, the duty cycle is the ratio of the pulse width to the complete cycle width
3. The percentage of time that a circuit is energized during one complete on/off cycle during pulse-width modulatin.

Duty-cycle solenoid:

The duty-cycle solenoid is a computer-controlled device in a feedback carburetor that alters the mixture adjustment. Also called a mixture control solenoid

Duty drawback:

Import duties or taxes repaid by a government in whole or in part, when the imported goods are re-exported or used in the manufacture of exported goods.

Duty paid value:

In respect to imported goods, is the aggregate value for duty on imported goods.

Duty waiver:

Forgiveness, in whole or in part, of import duties when certain conditions are met.

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