10 Parts of An Automatic Transmission & How They Work Together

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parts of an automatic transmission

If you’re like most drivers, you probably take your automatic transmission for granted. You put the car in “Drive,” and off you go – without having to worry about shifting gears. But what exactly is an automatic transmission, and how does it work?

In this article, we will discuss the parts of an automatic transmission and how they interact to produce smooth gear changes. We will also look at the cost of automatic transmission replacement and how to choose a reputable mechanic.

What is the Transmission System?

The transmission system in a car is responsible for transferring power from the engine to the wheels. It comprises a variety of gears, pulleys, and transmission fluids that work together to change the speed and direction of the power being transmitted. The transmission system is also responsible for braking and accelerating the car.

Types of Transmission System

There are two main types of transmission systems – automatic and manual.

Manual Transmission

A manual transmission system requires the driver to change gears manually, using a clutch pedal and gear shift. This type of transmission is less common than automatic transmissions, but it is still found in some cars today. Manual transmissions are often used in sports cars or trucks that need to handle high torque levels.

Automatic Transmission

Automatic transmissions use a torque converter to change the speed and direction of power being transmitted, whereas manual transmissions rely on the driver to change gears manually. Automatic transmissions are more popular than manual transmissions, as they are easier to operate and maintain. They also offer better fuel economy.

Types of Automatic Transmission

There are four different types of automatic transmission. These transmissions use different methods to achieve the goal of automatically changing gears.

Semi-Automatic Transmission

Semi-automatic transmissions are gaining in popularity as they offer the best of both worlds – the fuel efficiency of an automatic and the control of a manual. A semi-automatic transmission still uses a clutch pedal, but it is operated by an electronic actuator that monitors engine speed and throttle position.

When the engine reaches its optimum operating point, the actuator releases the clutch, similar to a traditional manual transmission. Semi-automatic transmissions offer the best fuel economy when used with the engine’s cruise control system.

One drawback of semi-automatic transmissions is that they can be more expensive than traditional automatic transmissions. There are also some concerns about their reliability, although this has not been a problem for most drivers.

Fully Automatic Transmission

The term “automatic transmission” typically refers to a type of vehicle transmission that utilizes a torque converter and hydraulic system to change gears. The driver doesn’t have to use a clutch to engage the transmission; it shifts gears automatically. This type of transmission is common in passenger cars and light trucks.

There are several different types of automatic transmissions. The most common is the planetary gearset, which uses a set of gears to change the speed and torque of the engine.

Continuously Variable Transmission

A continuously variable transmission, or CVT, is an automatic transmission that allows the driver to continuously vary the ratio of engine speed to wheel speed. This type of transmission is different from a traditional automatic transmission, which has a set number of gear ratios. A CVT can provide more than one possible ratio, allowing the driver to select the best one for the current driving conditions.

CVTs are becoming more and more common in cars and trucks, as they provide many advantages over traditional automatic transmissions. One of the biggest advantages is fuel economy. CVTs can help a vehicle to achieve better gas mileage than a traditional automatic transmission. They are also more efficient because they don’t require the same amount of energy to hold the transmission in gear.

Dual Clutch Transmission

A dual-clutch transmission, also known as a DCT transmission, is a type of automatic transmission that can be found in many high-performance cars. This type of transmission utilizes two clutches, one for odd-numbered gears and one for even-numbered gears. When the driver shifts gears, the appropriate clutch is engaged to provide the power needed for the next gear.

Dual-clutch transmissions are often praised for their fast and smooth gear changes. They are also known for being more fuel-efficient than traditional automatic transmissions. While they can be more expensive to repair, they offer many benefits that make them a popular choice among drivers.

How Does An Automatic Transmission Work?

There are a few different types of automatic transmissions, but they all work in basically the same way.

An automatic transmission works by using a torque converter to transfer power from the engine to the transmission. The torque converter is essentially a large metal disc that can spin at different speeds. The transmission fluid inside the converter helps transmit the engine’s power to the car’s driveshaft.

The transmission fluid also helps to cool the engine and the transmission. A pump powered by the engine circulates the fluid. The fluid passes through a filter to remove any debris, and then it is sent to the torque converter.

The converter works like a clutch, which allows the power from the engine to be transferred to the transmission. When the car is being driven, the fluid is sent to the rear of the converter, where it helps to spin the driveshaft.

If you are wondering how an automatic transmission works, this is a basic overview of how it functions. Many other components help make an automatic transmission work, but this gives you a general idea of how it works.

The main benefit of an automatic transmission is that it allows the driver to focus on steering and watching the road while the car takes care of shifting gears.

There are a few different factors that affect how an automatic transmission works. The car’s weight, the type of terrain, and the temperature all play a role in how the transmission operates. Automatic transmissions are also becoming more sophisticated and are now able to adapt to different driving styles. For example, if you drive in a hurry, the transmission will adjust its settings to provide faster gear changes.

Automatic transmissions are not without their drawbacks, however. They can be expensive to repair and maintain, and they often use more fuel than a standard manual transmission. They also require special fluid that can be expensive to replace.

Automatic Transmission Components

Several different components make up an automatic transmission. While the specific parts will vary depending on the make and model of the car, here is a basic overview of some of the most common components:

  1. Transmission Casing
  2. Torque Converter
  3. Automatic Transmission Fluid
  4. Oil Pump
  5. Planetary Gear Set
  6. Clutch Pack
  7. Output Shaft & Input Shaft
  8. Brake Band
  9. Valve Body
  10. Transmission Control Module

Let us see these components in a bit of detail.

1. Transmission Casing

transfer case

A transmission casing is a metal or plastic enclosure that houses the internal components of a transmission. It is generally cylindrical and has several openings for oil to flow in and out. The transmission casing protects the gears, bearings, and other components inside from damage. It also helps to dissipate heat generated by the transmission.

A transmission casing can be made from a variety of materials. It is usually riveted or bolted together, and the seams are sealed with gaskets to keep the oil inside.

The transmission casing is an important part of the transmission system and must be in good condition for the transmission to function.

2. Torque Converter

torque converter

A torque converter is a type of fluid coupling that transfers rotating power from one shaft to another. The operation of a torque converter is best understood by looking at its three main components: the impeller, turbine, and stator. The impeller is attached to the engine’s crankshaft and rotates at high speed. The turbine is connected to the output shaft and rotates at a slower speed.

The stator sits between the impeller and turbine and redirects the fluid flow, allowing the impeller and turbine to rotate independently. The torque converter clutch engages o to multiply the engine’s torque, making it ideal for low-speed driving. It also helps the engine start more easily and reduces wear on the drivetrain.

The main benefits of a torque converter are its ability to multiply engine torque, making it ideal for low-speed driving, and its ability to help the engine start more easily. It also reduces wear on the drivetrain.

There are three main types of torque converters: the lock-up torque converter, the variable displacement torque converter, and the electronic throttle control torque converter.

The lock-up torque converter is the most common type and locks the turbine and impeller together to create a direct mechanical connection between the engine and the output shaft. The variable displacement torque converter adjusts the amount of fluid passing through the stator, allowing it to vary its output torque. The electronic throttle control torque converter uses a motor to control the speed of the turbine, allowing for better fuel economy and reduced emissions.

3. Automatic Transmission Fluid

transmission fluid

An Automatic Transmission Fluid, or ATF, is a fluid used in automatic transmissions. It is a hydraulic fluid that acts as a lubricant and coolant for the gears and bearings inside the transmission. The fluid also helps to adjust the pressure within the transmission to allow it to shift gears smoothly.

Automatic transmission fluids come in various viscosities, depending on the climate and the make of the car. In colder climates, a thicker fluid is needed to prevent the transmission from freezing. In hotter climates, a thinner fluid is used in order to avoid the transmission from overheating.

4. Oil Pump

oil pump

An oil pump is a small electric motor that circulates engine oil throughout the car’s transmission. The oil pump helps to cool and lubricate the gears inside the transmission.

If the oil pump stops working, the transmission can overheat and fail. Most cars have an oil warning light that comes on if the oil pump isn’t working properly.

5. Planetary Gear Set

planetary gear set

A planetary gear set is a type of geared system found in a car’s transmission. It includes three or more gears (sun gear, ring gear & planet gears) that rotate around a central axis. This type of gearing allows for a wide range of speeds and torques to be achieved. The planetary gear set is often used in conjunction with other types of gears, such as helical gears, to create a more efficient system.

There are several benefits of using planetary gears in a car’s transmission. First, it allows for a large range of speeds and torques to be achieved. This is important because it enables the car to handle various driving conditions. Second, the planetary gear set is very efficient.

It can transmit large amounts of power while using minimal space and weight. Finally, the planetary gear set is reliable and durable. It can withstand heavy loads and extreme temperatures without breaking down.

6. Clutch Pack

clutch pack

A clutch pack is a type of friction clutch found in the transmission of many cars. It is made up of a stack of discs, each with many clutch pads on its surface. When the clutch pedal is depressed, the discs are forced together, causing the pads to grip the adjacent disc. This creates a frictional force that transmits torque from the engine to the transmission.

A clutch pack is used to regulate the amount of power transmitted to the wheels. When the clutch pedal is fully released, the discs are allowed to move freely, and there is no connection between the engine and the transmission. When the clutch pedal is partially depressed, the discs are partially compressed, and the power gradually increases. When the clutch pedal is fully depressed, the discs are fully compressed, and the power is transmitted to the wheels at its maximum level.

Clutch packs are also used to synchronize the rotation of the engine and the transmission. This ensures that the gears have meshed properly and that there is no slippage.

7. Output Shaft & Input Shaft


The transmission input shaft is the one that goes into the transmission, and the output shaft is the one that comes out. The input shaft carries the power from the engine to the transmission, while the output shaft carries the power from the transmission to the wheels. In a manual transmission, they are both one-piece, while there is a separate input shaft and output shaft in an automatic transmission.

The gears on the input shaft and output shaft mesh together to create the transmission’s gear ratio. This is what determines how fast the car will go with a given amount of power from the engine.

8. Brake Band

brake band

Most cars have a band brake in the transmission. This is a band of metal or cloth that presses against the inside of the driveshaft, slowing it down. It works in much the same way as a disc brake on a bicycle wheel.

The brake band is normally operated by hydraulic pressure from the brake fluid in the system. When you press on the brake pedal, the pressure builds up and forces the brake band against the drive shaft, slowing it down.

9. Valve Body

valve body

A valve body is a component of the automatic transmission in a car. It regulates the flow of fluid between different parts of the transmission. This helps to ensure that the gears are properly engaged and that the car moves smoothly. The valve body can become worn over time, which can lead to problems with the transmission.

If the valve body is worn, you may experience difficulty shifting gears, jerky movements, or a lack of power. It is important to have these symptoms checked out by a mechanic to determine if the valve body needs to be replaced.

10. Transmission Control Module


A Transmission Control Module, or TCU, is a computerized component of a vehicle’s automatic transmission. It monitors and controls all aspects of the transmission’s performance and can often be repaired or replaced without overhauling the entire transmission.

The TCU oversees many different functions of automatic transmission. It monitors the fluid pressure and temperature, adjusts the shift points and timing, and controls the torque converter lock-up. It can also diagnose problems with the transmission and report them to the driver.

If your TCU is bad, you will likely notice symptoms such as shifting problems, erratic or slow acceleration, or a failure to shift into gear. You can also check the TCU as part of routine transmission service.

Automatic Transmission Replacement Cost

You need to know a few things about automatic transmission replacement costs. The first is that there is a lot of price variation. The second is that the cost can be affected by several factors, including the make and model of your car, the type of automatic transmission, the shop you go to, and more.

That being said, there are a few general ranges that you can expect. A basic replacement can cost anywhere from $500 to $1,500. If your transmission needs to be rebuilt, the cost can range from $1,000 to $4,000. If you need a new or used transmission, the cost will be even higher. It’s important to note that these costs can vary widely, so it’s always a good idea to get a few quotes before you make a decision.

One way to save money on your transmission replacement is to do the work yourself. However, this can be a difficult task, and it’s not recommended for everyone. If you’re feeling up for the challenge, you can find some helpful guides online. Otherwise, it’s best to leave the job to the professionals.


Automatic transmission is a vital part of your car. It helps to ensure that the car moves smoothly and efficiently. If you’re having problems with your automatic transmission, it’s important to take action quickly. The sooner you get the problem fixed, the less chance of severe damage being done.

Automatic transmission replacement can be a costly affair, but it’s often worth the price to keep your car running smoothly. Be sure to get a few quotes before you make a decision, and always consult with a professional if you’re unsure about anything. With a little bit of care, your automatic transmission can last for many years. Thanks for reading! We hope this article was helpful.

Frequently Asked Questions

Can you replace the transmission of a car?

In some cases, you can replace the transmission of a car. However, it is important to consult with a mechanic to ensure that the replacement is done correctly. If done incorrectly, you could damage the car and end up spending more money in the long run.

What are the advantages of using automatic transmission?

There are a few advantages of using automatic transmission: they shift gears smoothly, and without drama, they’re more fuel-efficient than manual transmissions, and they offer a wider variety of driving modes. Automatic transmissions are also easier to operate than manual transmissions – all you have to do is step on the gas and brake pedals, and the car will take care of the rest.

Some people believe that automatic transmissions are less reliable than manual transmissions, but this is not always the case. In fact, some newer automatic transmissions are more reliable than older manual transmissions. Overall, there are pros and cons to both types of transmissions, so it’s up to you to decide which one is best for you.

Are automatic transmissions more prone to failure?

There is a lot of debate on this topic, with many people believing that automatic transmissions are more prone to failure. However, there is no real evidence to support this claim. In fact, research shows that automatic transmissions actually have a longer lifespan than manual transmissions.

People may think that automatic transmissions are more prone to failure because they often require more maintenance.

However, this is not always the case. Many people only take their car in for a transmission flush when the manual recommends doing so, while automatic transmissions may only need this service every two years or so.

In terms of cost, automatic transmissions can be more expensive to repair than manual transmissions.

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