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Transmission, Transaxle and Driveline Components and Industry Terminology

Being knowledgeable about your vehicle begins with having a good understanding of the different components and the names and terms used to describe them.


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ATTS - Honda's Automatic Torque Transfer System
The system distributes the engines torque output proportionately between the driven axles.

ATTS Fluid
The hydraulic fluid used in Honda's Automatic Torque Transfer System.

Auto Shift Lock/Starter Safety Switch
A safety device that locks the shifter in the Park position until the brake pedal is depressed.  It also prevents the vehicle from starting unless the vehicle is in Park or the neutral position.

Automated Manual Transmission
Also referred to as "DSG," "direct shift gearbox," "SMG" and "sequential manual gearbox."  A conventional clutch-type manual transmission that employs electronic, pneumatic and/or hydraulic actuators in place of a conventional clutch pedal, and a purely mechanical shift lever. The driver may select either fully automatic shift mode or driver-controlled shift mode.

Automatic Transaxle (Same as Transaxle)
Found in front wheel drive (FWD) vehicles.  A transaxle is an automatic transmission that is combined with the drive axle assembly.  See "Automatic Transmission"

Automatic Transaxle Pressure Filter
The external filter on an automatic transmission.

Automatic Transmission
An automatic transmission (also called automatic gearbox) is a complex motor vehicle transmission that automatically changes gears without the need for driver input. The transmission delivers the engines power and torque to the drive wheels using different gear ratios.  Some of the major components in an automatic transmission include a torque converter, an oil pump, a planetary gear set assembly and friction clutches and bands. Today, more than 90% of all new vehicles sold in North America are equipped with automatic transmissions/transaxles.

Automatic Transmission Bands
Adjustable circular metal straps lined with a friction material that are hydraulically actuated to tighten around and stop the rotation of a drum as part of the shifting process.

Automatic Transmission Clutches and Clutch Packs
Clutches (or friction clutches) are round discs that engage and disengage with gear changes.  When engaged, the friction material on the clutch disc locks it to the appropriate gear enabling the engine's power to be transmitted to the drive wheels.  When clutches wear out, slipping occurs. 

Automatic Transmission Auxiliary Oil Cooler
An aftermarket "secondary" transmission oil/fluid cooler designed to increase the cooling capabilities of the factory installed transmission fluid cooling system.

Automatic Transmission Oil Cooling System
The factory transmission oil/fluid cooling system that uses the engine's radiator to cool the transmission oil.  The hot transmission oil is routed through a section of the radiator where the fluid is cooled before being routed back to the transmission.

Automatic Transmission Cooler Hoses
High-pressure aluminum tubes or flexible hoses that carry transmission fluid to and from a heat exchanger or oil cooler.

Automatic Transmission Filter
A component in most automatic transmissions that is fitted over the fluid intake, (usually located in the oil pan), that prevents debris and other contaminants from circulating through the transmission's inner workings and potentially causing excessive wear, blockages and damage.  Some transmissions use a reusable metal or nylon mesh-type screen in place of a disposable/replaceable filter.

Automatic Transmission Fluid (ATF)
Automatic transmission fluid (ATF) is the fluid used in vehicles equipped with automatic transmissions. The fluid is typically red in color so it can be easily distinguished from engine oil and other vehicle fluids.  Transmission fluid is specially formulated to lubricate and cool the transmission while providing the hydraulic pressure needed to shift gears and engage and disengage bands and clutches.  ATF is used in many manual transmissions, 4-wheel drive (4WD) transfer cases and power steering pumps.

AWD or All-Wheel Drive
A drivetrain that employs a front, rear and center differential to provide the engine's power to all four wheels of a vehicle.

Automatic Transmission Rebuild Kit
A preassembled set of  parts that are used in rebuilding an automatic transmission.  Depending on the vehicle, year, make and model and the kit chosen, automatic transmission rebuilder kits typically include a paper and rubber kit, seal kit, steel plates, friction clutches, filter, modulator, bushing kit, bonded pistons, flex band and popular washers.  Rebuilder kits do not include hard parts.

Automatic Transmission Repair Shop
An automotive repair shop that specializes in servicing and repairing automatic transmissions.  Transmission repair shops employ technicians with specialized training in automatic transmission service and repair.  General automotive repair shops typically do not provide specialized transmission services.

Automatic Transmission Technician
A trained (and oftentimes) certified automatic transmission professional.  This is the person that will diagnose your transmission problems and make the necessary repair(s).  These technicians have extensive training in diagnosing, servicing and repairing/rebuilding all makes and models of automatic transmission and transaxles.

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Axle Drive Fluid
The liquid used for lubricating gears inside the axle.

Axle Ratio
The gear ratio of a gear train assembly. By using input and output gears with different teeth counts, various gear and axles ratios are achieved.

Code Reader Scanner
Also called OBD-II Scanner.  A device used to read a vehicle's onboard computer and extract the code(s) that have triggered a check engine light situation.

Constant Velocity Joint (or CV Joint)
Located on either end of the drive axles, cv joints transmit engine power while enabling full steering and suspension movement. Black accordion type rubber covers (cv boots) cover and protect these joints from debris and damage.  CV boots are filled with lubricant to keep the cv joint greased.

Continuously Variable Transmission or CVT
A transmission with a continuously variable drive ratio (as opposed to conventionally stepped gear ratios) that maintains a steady acceleration curve with no pauses for gear changes. Declutching/Freewheeling The act of disengaging a vehicles transmission from its driveshaft, either manually or automatically, when its drive shafts RPM exceeds the transmissions RPM.

Differential Fluid
The liquid used for lubricating gears inside the differential.

Drop-Down Cable
A transmission cable connected to the throttle that shifts the transmission into a lower gear when the accelerator is depressed suddenly beyond a certain point.  Most people know this as passing gear.

Drive Axle Boots
The flexible, conical, accordion-like covers that contain lubricant and protect the constant-velocity joints on a drive axle shaft.

Drive Shaft
A long round "tube-like" metal part that connects the transmission to the differential on a rear-wheel or four-wheel drive vehicle.  On either end of a drive shaft are u-joints or universal joints.

Drive System
The type of drive system or drivetrain of a vehicle; two-wheel drive, four-wheel drive or all-wheel drive.

Drive Train Mounts
Components typically made of metal and hard rubber material to attach a vehicles drivetrain components to the vehicle chassis.  These "mounts" absorb much of the energy produced between the mounted parts and the chassis.

The parts of a vehicle that generates power and transfers the power to the vehicle's wheels.

Drivetrain Warranty
A manufacturer's warranty or aftermarket warranty that covers the drivetrain, i.e., engine, transmission, driveshaft, differential and drive axles.

Extended Warranty
A vehicle warranty sold by the vehicle manufacturer/dealership or by a third party service provider that extends the vehicles basic warranty beyond the manufacturer's standard warranty period.

FWD or Front Wheel Drive
Front-engine front-wheel drive.  A vehicle that is propelled solely by its front wheels and whose engine is located forward of its front axle.  Front wheel drive automatic transmissions are called transaxles because the transmission and axles are one component.

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Four Wheel Drive or 4WD
A vehicle that uses two differentials and a transfer case to transfer the engine's power to all four drive wheels.  Normally these vehicles can be driven in either two-wheel drive or four-wheel drive mode.

Haldex Clutch
Limited slip coupling used in vehicles with automatic all-wheel drive systems to engage and disengage a secondary axle when needed.

Hard Parts
Automatic transmission parts fall into one of two categories; soft parts and hard parts.  The hard parts are the parts that are not part of a standard rebuild kit and that typically do not need to be replaced as part of a standard transmission overhaul.  Hard parts include the pump, clutch drum, output shaft, planetary gears, etc.

Hybrid Drivetrain
The drivetrain layout in a hybrid vehicle: parallel, series or combined.

Limited Warranty
A vehicle warranty that is in effect for a specified number of years and/or miles driven.

Number of Speeds
The number of forward gears of a transmission.  Most automatic transmissions have 4-speeds, but 5, 6, 7 and even 8-speed automatic transmission are available in some high-end luxury and sports cars.

OEM stands for Original Equipment Manufacturer.  OEM replacement parts are considered to be of higher quality that most aftermarket auto parts.

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Off-road Ready
A vehicle with capable of traveling off-road.  These vehicles are typically 4 wheel drive with all-terrain tires and high ground clearance.

Powertrain Warranty
Also referred to as the "drivetrain warranty", a powertrain warranty covers the parts of the vehicle that make it move, including the engine, transmission, drive axles and driveshaft.

RPM stands for "Revolutions Per Minute", which is the number of revolutions the pistons of an engine turn in one minute.

RR stands for "Rear-Engine Rear-Wheel Drive", which means what it says; the engine is in the rear of the vehicle and the engines power is transferred to the rear wheels only.  Some vehicles with a RR drivetrain configuration include some Porsche models and the Volkswagen Beetle.

RWD or Rear Wheel Drive
A vehicle that uses a transmission and driveshaft to deliver the engine's torque and power to a rear differential and then to the rear wheels.  Examples of rear wheel drive vehicles include the Chevrolet Camaro and Corvette, the Ford Mustang, Dodge Challenger, Lincoln Town Car and of course pick-up trucks.

Scheduled Maintenance Warranty
A warranty that covers service procedures recommended by the manufacturer at predetermined intervals to preserve and/or prolong the life of a vehicle.

Sequential Manual Gearbox
Also referred to as "SMG," "direct shift gearbox," "DSG" and "automated manual transmission." See "Automated Manual Transmission."

Service Reminder Light
A light that indicates that general vehicle maintenance is needed or that a specific service is required.

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Shift Control Mechanism
The location of the shift control mechanism, which includes levers, paddles or buttons.

Shift Linkage
Any collection of mechanical connections between a vehicles operating control(s) and its transmission.

Shift Protocol
The means by which a driver changes gears, including buttons, paddles or a lever.

Shiftable Automatic Transmission
An automatic torque converter transmission equipped with a feature that permits the driver to actively select either fully automatic or driver-controlled shift modes by using a dual-gate shifter and/or remote shifter controls.

Skid Plate
A shield typically attached to the bottom of a vehicles front bumper that is designed to guard the undercarriage in the case of insufficient ground clearance.

Slipping or Transmission Slip
Slipping is a term used to describe an automatic transmission that is unable to transfer the engine's torque (or output) to the drive wheels either partially or fully.  Low transmission fluid, a clogged transmission filter and burnt or worn out clutches can cause slipping.

Sequential manual gearbox is an automated manual transmission.  It is an automatic gearbox that can be shifted manually.  Typically only found in high-end sports cars.

Stability Control
Also known as "electronic stability control," or "ESC." A safety feature that improves the safety of a vehicles handling by detecting skids and compensating by adjusting braking pressure to help maintain the intended direction of the vehicle. Some stability control systems also reduce engine power until control is regained.

Starter Safety Switch
Also called Neutral Safety Switch.  A vehicle safety feature that prevents a vehicle from being started unless the shifter lever is in Park or Neutral in vehicles equipped with automatic transmissions or the clutch pedal depressed in  vehicles equipped with standard/manual transmissions.

An instrument that tells the driver how many revolutions per minute (RPMs) the pistons of the engine are turning.

Technical Service Bulletin
Sometimes referred to as "TSB" is a bulletin put out by vehicle manufacturers to advise vehicle owners of a problem with a particular vehicle year and model.

Throttle & Kick-Down Lever Ball Studs
Lubricated pivot points for the throttle or kick-down linkages of the transmission.

A measurement of an engine's power that indicates how forcefully it can rotate the crankshaft at a given engine speed.

Torque Converter
The torque converter is to an automatic transmission as a clutch is to a manual/standard transmission.  The torque converter controls the automatic transmission fluid/pressure that reaches the transmission, which effectively controls the engagement of clutches and gears. 

Towing Capable
A vehicle with features and equipment that make it well-suited for pulling a trailer.  Towing capable vehicles with automatic transmissions are usually equipped with an external transmission oil cooler.

Towing Capacity
The maximum amount of weight a vehicle is capable of towing (according to its manufacturer).  Exceeding the vehicle's towing capacity can cause the vehicle's gearbox to overheat.  As you will read throughout this Web site, excessive heat is an automatic transmission's worst enemy.

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Traction Control System or TCS
A safety feature that regulates wheel spin and prevents loss of control under acceleration by ensuring maximum traction and contact between the tires and the road surface.  This is accomplished by adjusting brake pressure, reducing the throttle and/or reducing the fuel supply to one or more cylinders in order to reduce the power to the drive wheels.

Trailer Hitch
A metal device attached to a structurally sound section of a vehicles frame that is used to support a trailer while coupling it to the vehicle.

Transfer Case Fluid
Lubricant used in the transfer case.

Transmission Modes
Driver-selectable transmission settings that change drive ratios and/or shift points for fuel economy or performance.

Transmission Oil Pan
Where the filter and valve body reside.  The pan typically holds between 3 to 4 quarts of the transmission fluid used in the transmission.

Transmission Overdrive
A final gear ratio for an automatic transmission that has an output speed greater than its input speed, which increases highway fuel economy.  Most automatic gearboxes today have an overdrive gear.

Transmission Type
Describes a type of transmission, i.e., automatic, manual, semi-automatic, shiftable automatic or automated manual, CVT.

Universal Joints or U-joints
Flexible joints used on drive shafts that are composed of two U-shaped yokes that share a common cross-shaped member.

The area of a vehicle that is typically not visible from above and that is exposed to the road.

Vacuum Lines & Hoses
Flexible tubing used in vehicle engines and transmissions to carry air, fluids, vapors or pressurized gas.

Valve Body
The part of an automatic transmission or automatic gearbox which serves as the hydraulic control center.  The pressurized fluid received at the valve body is directed to the clutches and transmission bands in a way that engages the appropriate gear configuration for the travel condition. The valve body receives pressurized fluid from the main pump of the transmission operated by the torque converter and then directs the pressurized fluid with the use of valves and servos to the appropriate clutches and bands of transmission to engage the most appropriate gear configuration for the driving conditions.

Vehicle Identification Number or VIN
Also referred to as "VIN."  This is the number that identifies the vehicle manufacturer, year, model, place of manufacture, etc.  Using this number when ordering parts helps insure you are ordering the correct parts.  Get the details for any vehicle -
free VIN decoder.

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  Transmission Resource Library  
How Automatic Transmissions Work
Types of Automatic Transmissions
Which Transmission Do I Have?
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How Long Do Automatic Transmissions Last?
Automatic Transmission Maintenance
How to Check Transmission Fluid Level
How to Check Transmission Fluid Condition
Automatic Transmission Fluid/Filter Change
Automatic Transmission Fluid Flush
Automatic Transmission Fluid (ATF)
Transmission Fluid Color
What Can Go Wrong With My Transmission?
Transmission Failed-Is My Vehicle Worth Fixing?
Troubleshoot Transmission Problems
Transmission Failure - What Are My Options?
Find a Reputable Transmission Shop
8 Tips for a Long-Lasting Transmission
Automatic Transmission Rebuild Costs
Remanufactured Automatic Transmissions
Are you sure you need a transmission rebuild?
Transmission Terms You Should Know
Why Should I Install a Shift Kit?
Transmission Parking Pawl
Keep Your Transmission Cool or Pay the Price
Free Vehicle Owners Manuals
DIY Automatic Transmission Removal (RWD
DIY Automatic Transmission Install (RWD)
Sensors and Solenoids
CV-Joint Symptoms and Replacement
Aftermarket Warranties
Emergency Fixes
DIY Speed Sensor Replacement
How to Flush an Automatic Transmission
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