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Ta     Th     Ti    To     Tr     Tu     Tw

Tachometer  An instrument that indicates the number of revolutions per minute at which the engine is turning.

Tailpipe  The rearmost part of the exhaust system, through which exhaust gases are vented into the atmosphere. Many specialty product manufacturers offer attractive tailpipe designs in various diameters and in various finishes, including chromed steel and polished stainless steel. Changing the tailpipe can enhance a vehicle's styling, and it also can affect the loudness of the exhaust.

Tappet A cylindrical component which transmits motion from the cam to the valve stem, either directly or via a pushrod and rocker arm. Also called a cam follower.

Thermostat   The thermostat is an important part of the engine's cooling system.

 It closes the coolant flow to the radiator when the engine is cold, and opens it when the engine reaches normal operating temperature. This is a small and inexpensive part, but its failure may cause engine overheating, which in turn may result in serious engine damage. As soon as you note the engine temperature starts rising more than normal level, have your vehicle inspected, possible it needs new thermostat.

Throttle  The device that controls the vacuum created in the venturi of the carburetor. The greater the vacuum, the richer the fuel-air mixture. The throttle enables the engine to run on a richer mixture and produce more power for high-speed driving. It consists of a throttle arm located on the outside of the carburetor and connected to the gas pedal (or throttle twist grip on a motorcycle), which in turn activates a throttle butterfly valve at the base of the carburetor barrel where it joins the intake manifold.

Throttle Arm The lever that actuates the throttle.

Throttle-Body Throttle-Body Fuel Injection is a type of Electronic Fuel Injection which positions the injector(s) centrally in a throttle-body housing. This housing contains a valve to regulate the airflow through the intake manifold.

Throttle Butterfly  A valve in the throat of the carburetor which regulates the amount of the flow of gasoline. See throttle valve.

Throttle Pedal  The gas pedal which operates the throttle butterfly through a series of linkages.

Throttle Plate A term used for throttle valve.

Throttle Valve

[1] A valve in the carburetor. It is used to control the amount of air-fuel mixture that reaches the cylinders. Usually consists of a flat round disc mounted on a shaft so that it can be tilted at various angles in the carburetor throttle valve body. It is connected by suitable linkage to the accelerator pedal.

[2] A modulator valve in an automatic transmission which is actuated either by the accelerator pedal, by the vacuum in the engine intake manifold, or by the carburetor throttle; it converts line pressure into an engine-load dependent pressure, which is directed to various valves

Thrust Bearing  The bearing in the clutch assembly that is moved in to the release levers by clutch pedal action to disengage the clutch. Also referred to as a release bearing.


Tie Rod Ends Tie rod ends are utilized in the steering linkage, steering knuckle pivot supports, and various other hinge mechanisms. Ball joints that join the key parts of the steering linkage pass on the steering wheel's motion no matter what the angle of the linkage or the vibration from the road.

Timing Belt   A toothed belt which drives the camshaft. Serious engine damage may result if it breaks in service.

The automobile engine uses a metal timing chain, or a flexible toothed timing belt to rotate the camshaft. The timing chain/belt is driven by the crankshaft.

The timing chain, or timing belt is used to "time" the opening and closing of the valves. The camshaft rotates once for every two rotations of the crankshaft.

Discover How The Timming Belt Works in The Engine

Timing chain  A chain which drives the camshaft. See Timing Belt above

Tires  A tire is a tubular corded carcass covered with rubber or synthetic rubber, which is mounted on a wheel and inflated to provide traction for moving a vehicle and for assisting the brakes in stopping it.

A-2 tire

Tire Ratings Tires are rated by load capacity, size and speed capacity. For example, a P225/50VR16 printed on the side of the tire means:

P = P-Metric (Passenger Type Tire)

255 = Section Width (255mm)

50 = Aspect Ratio (tire height/section width)

V = Speed Rating

R = Type of Ply (Radial)

16 = Wheel Diameter (16 inches)

Tire and wheel dimensions are the first point of information in any discussion of size and capacities. Among the other terms used to describe tires are: tread, shoulder, carcass, sidewall, bead seal, bead seat, tire diameter, aspect ratio, speed rating and section width

Toe-in  The amount the front wheels are closer together at the front than at the rear. On rear wheel drive vehicles, a slight amount of toe-in is usually specified to keep the front wheels running parallel on the road by offsetting other forces that tend to spread the wheels apart.

Toe-out  The amount the front wheels are closer together at the rear than at the front. On front wheel drive vehicles, a slight amount of toe-out is usually specified.

Top Dead Center: ( TDC ) Highest point of piston and connecting-rod travel in a cylinder; the ends of the compression and exhaust strokes in a four-cycle engine.

Torque A force that produces a twisting or rotating motion.

[1] Turning or twisting force such as the force imparted on the drive line by the engine. Usually measured in lb-ft. It differs from work or power in that torque does not necessarily produce motion. Basically, the magnitude of a torque acting on a body is the product of the magnitude of a force and its force arm (perpendicular distance from the axis of rotation of the body to the line of action of the force). This product is called the moment of the torque about the axis or the torque.

[2] To tighten a nut or bolt with a torque wrench.

Torque Converter A unit in an automatic transmission, quite similar to the fluid coupling, that transfers engine torque to the transmission input shaft. It also cushions the flow of power. Unlike the fluid coupling, the torque converter can multiply engine torque. This is accomplished by installing one or more stators between the torus members. In the torque converter the driving torus is referred to as the "pump" and the driven torus as the "turbine." The engine drives the impeller which in turn impels fluid against the vanes of a turbine connected through transmission gears to the driveshaft of the automobile. The stator redirects oil flow from the turbine to boost impeller action and multiply engine torque.


torque converter drive plate: See drive plate


torque converter housing: A bell housing


torque converter lock-up clutch: An automatically engaged clutch in a lock-up torque converter which prevents slipping losses

Torque Converter Clutch An electronically controlled lockup clutch that is automatically engaged at certain speeds to eliminate the slip between the torque converter's input and output, thereby improving fuel efficiency and performance.

Torque, Engine Engine torque is the amount of twisting effort exerted at the crankshaft by an engine expressed in foot-pounds of force. A foot-pound represents the force of one pound acting at the right angle to the rotating crankshaft at distance of one foot in length.

Torque Rating A measure of the engine's power capability, whereby the amount of twisting or rotating effort being exerted on the crankshaft is expressed in lb.-ft. of force. Torque is the force that gets the weight of the vehicle moving, making it an important consideration in trailering.

Torsion Bar A rod in the suspension system that, when twisted from a grip at one end, functions like a spring.

A long spring steel rod attached in such a way that one end is anchored while the other is free to twist.

 One end is fastened to the frame at one end and to a suspension part at the other. If an arm is attached, at right angles, to the free end, any movement of the arm will cause the rod or bar to twist the bar's resistance to twisting provides a spring action. The torsion bar replaces both coilleaf springs in some suspension systems. The main advantage of the torsion bar over the coil spring in the front suspension is the ease of adjusting front suspension height.

Torsion Bar Suspension A suspension system that makes use of torsion bars in place of the leaf or coil spring.

Torus The inner surface of a hollow doughnut-shaped structure, especially found in automatic transmissions. See fluid coupling.

Tracer  A stripe of a second color applied to a wire insulator to distinguish that wire from another one with the same color insulator.

Trailing Arm A rear suspension element consisting of a lengthwise member that pivots from the body at its forward end and has a wheel hub rigidly attached to its trailing end.

Transaxle A transmission and differential combined in one integrated assembly, eliminating the need for a separate connecting drive shaft. This configuration is typical in front-wheel-drive vehicles.

Transformer   An electrical device with an arrangement of copper coils with an iron center, used to increase or decrease electrical voltage. A vehicle ignition coil transforms the voltage from 12 volts to upward of 20,000 volts.

    Electromagnetic device which transfers electrical energy from primary circuit into variations of voltage in secondary circuit.

Transmission  The gear-changing or gear-shifting system through which engine power is transferred to the wheels. The purpose of gear-changing is to keep maximum engine power applied to the wheels at all times for all conditions, from start-up to high speeds.

See also Automatic Transmission Manual Transmission

Discover How The Transmission Works in Your Vehicle

Transmission Fluid Dip Stick The transmission fluid dip stick is a long metal rod that goes into the transmission. It serves check how much transmission fluid is in the transmission. The dip stick is held in a tube; the end of the tube extends into the transmission. It has measurement markings on it. If you pull it out, you can see whether you have enough transmission fluid, or whether you need more by the level of fluid on the markings. Most manual transmissions do not have dipsticks, instead they use a filler hole which is at the same level as the correct oil level. When the oil is topped up or refilled, the mechanic simply adds oil until the filler hole's level is reached.

Transmission Gears  Most cars have from three to five forward gears, and one reverse gear. The transmission changes the ratio of the engine speed and the wheels by connecting gears in various combinations. First gear connects the engine power to the drive wheels via a pair of reduction gear sets, which gives increased power and reduced wheelspeed when the car is beginning to move. Gears work exactly like levers. A small gear driving a larger one gives an increase in torque, and a decrease in speed, and vise-versa. Transmission gears are heat-treated, high quality steel. They have smooth, hard teeth, cut on precision machinery while red hot. There are many types of gear teeth, but most transmissions use spur and helical gears. Most of the gears are the helical type, because they last longer and are more quiet than spur gears. There has to be enough room (a few thousandths of an inch) between the gear teeth for lubrication, expansion, and any irregularities in size.

Transmission tunnel The transmission tunnel is a cone-shaped formation in the front of the floor pan. Its shape duplicates the transmission, but it is a little bit bigger and provides about two inches of clearance around the transmission. The transmission tunnel does not exist in front wheel drive cars, because the transmission is on the side of the engine completely under the hood. Only rear-wheel drive cars have transmission tunnels. A manual transmission tunnel has a hole in it to allow the shift linkage to be worked from inside the car. The shifter linkage goes through the transmission tunnel. A rubber boot on the shifter linkage stops dirt, dust and exhaust fumes from entering the passenger compartment. The rubber boot is mounted onto the transmission tunnel and fastened securely around the gearshift linkage. Vehicles with automatic transmission do not need a transmission tunnel because the shift linkage does not usually go through the transmission tunnel. The shift linkage in automatic transmission usually goes in front of the firewall from the base of the steering column.

Transverse Engine An engine that is mounted laterally (i.e., left to right) between the drive wheels (rather than longitudinally - front to back), often found on cars with front-wheel drive.
Also called "east-west layout"

Tread The pattern on the surface of a tire

Also the width of a car measured from the center line of the wheels. Sometimes called the track.

 Tune-up  A process of accurate and careful adjustments and parts replacement to obtain the best possible engine performance.

[1] The driven member inside a torque converter consisting of many vanes that receive fluid flow from the impeller.
[2] A driven member that connects to the transmission input shaft and provides torque input to the planetary gearset. 

A type of engine in which all the parts that are in regular motion are rotating, making for very smooth operation. The basic gas turbine operates as follows: air enters the compressor and is compressed. It is then delivered to the combustion chamber under pressure and here the fuel is introduced, mixed with the air and burned, the quantity injected determining speed and power output. The hot, high-pressure burning gases then proceed to the first turbine, which drives the compressor and continue to the power turbine, which delivers power to the output shaft through reduction gears. The gears are necessary because the speed of turbine rotation is measured in tens of thousands of rpm not thousands as with a typical piston engine. The turbine's attractions include its utter simplicity and directness in getting power from burning gas, its smoothness, easy cold starting and its ability to run on almost any hydrocarbon fuel. On the minus side are high cost, problems with materials because of the high temperatures and speed of rotation and relatively high NOx production. Also see gas turbine

Turbine Engine  An engine in which gas pressure is created by combustion to spin a turbine.

Any of various machines in which the kinetic energy of a moving fluid is converted to mechanical power by the impulse or reaction of the fluid with a series of buckets, paddles, or blades arrayed about the circumference of a wheel or cylinder.

An engine that uses burning gases to spin a turbine, or series of turbines, as a means of propelling the vehicle.
Also see turbine.


Turbocharger  A centrifugal device, driven by exhaust gases, that pressurizes the intake air. Normally used to increase the power output from a given engine displacement, but can also be used primarily to reduce exhaust emissions (as on VW's "Umwelt" Diesel engine).

Twist Beam Rear Axle
Twist-Beam Rear Axle  See semi-independent suspension

Two-Stroke Cycle  An internal-combustion engine that requires only one revolution per cylinder or two piston strokes (up and down) to achieve a power stroke. Rarely used in automobiles.


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