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Da     Di     Dr     Du


Dashboard The section immediately behind the windshield that houses the instruments, accessory controls, and glove box.

Dash Controls  The dash board, behind the steering wheel displays the control panel of the car. Duplicate fragments of the control panel are found in the interior of your vehicle, such as automatic door locks, extra light switches, etc. Many functions of the car are carried out through the dash board, like turning on the headlights, windshield wipers, horn, turn signals, air conditioning, cassette player, etc. It also contains all of your gauges; gas, temperature, tachometer, etc., which enables the monitoring of the operating conditions of your engine and charging system, fuel level, oil pressure and coolant temperature. It ensures that all the controls are within the drivers reach.

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

Diagonal Brake System kit A dual-brake system with separate hydraulic circuits connecting diagonal wheels together; right front to left rear and left front to right rear.

Diesel Engine  An internal-combustion engine in which the fuel is injected into the cylinder near the end of the compression stroke and is ignited by the heat of the compressed air in the cylinder. No spark plug or carburetor is needed.

Diesel Fuel Injector The diesel fuel injector is a pressure valve, but it has specific components that allow it to disperse the diesel fuel in set patterns, depending on the design of the valve. Diesel fuel injectors receive the pressurized impulse from the diesel fuel pump, and allow the fuel to enter the combustion chamber when it is needed. If the diesel fuel injectors get clogged, engine performance suffers.

Diesel Fuel Pump Diesel fuel pumps inject a specific amount of fuel during a specific time, and control the injectors by the pressure waves of the fuel that they pump. The diesel fuel pump has mechanisms in it, which allows more or less fuel to be pumped. If less fuel is pumped into the cylinders, this slows the engine, and vice versa. It thus also regulates the speed. A series of gears link them to the crankshaft or the camshaft, allowing the fuel pump to be driven directly by the crankshaft of the engine. Some may be belt or chain driven.

Differential The differential is the thing that works both drive axles at the same time, but lets them rotate at different speeds so that the car

can make turns.  When a car makes a turn, the outer wheel has to turn faster than the inner wheel, due to the difference in the length of the paths they take.

The differential is located between the two wheels, and is attached to each wheel by a half-shaft rotated through a bevel gear. Four-wheel drive cars have a separate differential for each pair of wheels. A grooved, or splined, axle side gear is positioned on the splined end of each axle. The side gears are driven by "spider" gears, which are little gears mounted on a shaft attached to the differential case. As it is supported by the differential case, the side gear can turn inside the case. The differential case can be turned, revolving around the axle gears. The differential pinion (a pinion is a small gear that either drives a larger gear or is driven by one) shaft turns the ring gear, which is fastened to the differential case. The propeller shaft (drive shaft) connects the transmission output shaft to the differential pinion shaft. The turning differential case is mounted on two large bearing holders. These bearings are called carrier bearings. The propeller shaft rotates the ring gear pinion, and the pinion turns the ring gear. The ring gear then turns the differential case and pinion shaft, but the axle side gears will not turn. By passing the differential pinion shaft through two differential pinion gears that mesh with the side gears, the case will turn and the axle side gears will turn with it. During turns, the side gears turn at rates dictated by the radius of the turns, and the spider gears then turn to allow the outer wheel to turn faster than the inner one.

Differential Gears  The gears that convey 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 Housing See Differential photo above and axle housing.

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.

Disc Brake  A type of brake in which two friction pads grip a steel disc that is attached to the wheel, with one pad on each side.

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."


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.

Drivebelt(s)   The belt(s) used to drive accessories such as the

alternator, water pump, power steering pump, air conditioning compressor, etc. off the crankshaft pulley.


Drive Train  That combination of gears, clutches, shafts, etc., that transmits the engine power to the wheels.

Driveshaft  Any shaft used to transmit motion. Commonly used when referring to the axleshafts on a front wheel drive vehicle.

The drive shaft, or propeller shaft, connects the transmission output shaft to the differential pinion shaft. Since all roads are not perfectly smooth, and the transmission is fixed, the drive shaft has to be flexible to absorb the shock of bumps in the road. Universal, or "U-joints" allow the drive shaft to flex (and stop it from breaking) when the drive angle changes.
There are two types of drive shafts, the Hotchkiss drive and the Torque Tube Drive.

Drive Wheel/Axle The drive wheel is the end of the axle shaft; it has lugs protruding from it. The lugs are separate pieces that are mounted in the drive wheel. The drive wheel bolts onto the brake drum and the wheel rim of the car itself. It is usually a disc about six or seven inches in diameter. Occasionally the drive wheel and the axle shaft are all one piece

Driving Wheel The wheel(s) which is driven by the engine through the drivetrain.   Also called the "driven wheel"

Drum Brake  A type of brake using a drum-shaped metal cylinder

attached to the inner surface of the wheel. When the brake pedal is pressed, curved brake shoes with friction linings press against the inside of the drum to slow or stop the vehicle.

Dual Exhaust An exhaust system that features two pipes running to the rear of the vehicle. A "true" dual exhaust system will route exhaust from one side of a V6 or V8 engine to the rear of the vehicle through one pipe and route exhaust from the other side of the engine through another pipe. On any relatively new vehicle, a true dual exhaust system will feature at least two catalytic converters, as well as two mufflers and two tailpipes. Some other dual-exhaust setups feature one muffler with two entries and two exits.

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The objective of this Web Page is to familiarize you with basic auto maintenance
-  in some common emergencies -
not to make you an expert in auto mechanics

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