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How does an automatic transmission work

How does an automatic transmission work?

Do you know what an automatic transmission is and how does it work? Besides, have you wondered how all of its parts work together to push forward your vehicle?

The following article will shed light on the topic in detail and will cover all the essentials that make an Automatic Transmission work, such as Torque Converter, Planetary Gear Set, Valve Body, and more.

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Automatic transmission parts

There are 8 main parts of an automatic transmission system that are necessary for proper functioning. Read on to know more about the functioning of every part of an automatic transmission.

Torque converter

In an automatic transmission, the torque converter replaces the clutch to perform an identical function. During the movement, your transmission can not switch gears, else, the gears will snap. If your torque converter shows signs of a problem, get it checked by a professional.

A torque converter lets your engine keep running as well as disconnecting itself from the transmission. It is the same thing as disconnecting the transmission from the switch gears by damaging the clutch when it’s on the manual transmission.

Moreover, the torque converters don’t need human assistance (in the form of nuts, bolts, or even gears) when it comes to connecting the engine with the transmission; because transmission fluid is enough for all the work. However, the functioning of a torque converter itself is a  bit tricky.

Oil pump

The automatic transmission oil pump’s function is similar to an ordinary oil pump. Its function is to put the transmission fluid from the transmission pan into the valve body and throughout the various components of the transmission.

The oil pump is not an excessive component, but it is an essential part of the system, yet it is one of the fragile components, which is likely to break down if not taken care of properly.

Planetary gear set

The automatic transmission consists of one or multiple (usually multiple) planetary sets of gear.

Planetary gears consist of 3 gear sets. Sun gear is the ruling gear that is located in the middle of the planetary carrier. The second set of gear is planetary gear. There are usually more than 3 such gears and the netting in the middle of the sun and ring gear.

The ring gear revolves around the planetary gears with 1 ring, which connects the whole system.

It locks 2 or 3 gear sets simultaneously. As each gear set differs from the other, the gear mass ratio locks other gears in the position.

Clutch packs

A clutch pack consists of multiple plates held together. This happens at the time when the valve body delivers oil pressure to the clutch pack, it holds a particular number of clutch packs at one place, which gives the driver his/her desired output amount. Different quantities of oil pressure hold different amounts of discs giving the hub a another gear ratio. 

As the oil pressure amounts differ, it involves different figures of discs, giving the mid part of a wheel a non-identical gear ratio.

Output shaft

When the transmission has done its job, it sends power to the driveshaft that is run by the transmission’s output shaft. Which then provides power to the center parts.

When the transmission completes what its job is, it sends current to the driveshaft, which supplies power to the hub (as a result).

Brake band

Brake bands are used for keeping the grip on planetary gears. The planetary gears enable the engine revolutions per minute (RPM) to come in line along with the gear ratio.

The function of brake bands is quite similar to drum brakes. The piston pushes the band which is all over a drum. The more hardly the piston will push, the more power will be put on.

Oil pan

The transmission consists of an oil pan at the bottom. It holds the extra transmission oil for the pump as a reserve, so it can be used when it’s required. It usually consists of a transmission fluid filter connected, either inside or outside.

This is one of the most common components of a transmission, but at the same time, it is a part, which requires maintenance from time to time. The gasket wrapped around the oil pan discharges transmission oil and demands to be exchanged.

Valve body

The engine consists of an Engine Control Unit (ECU), while the automatic transmission contains a valve body. This component’s job is to direct the whole enforcement from the oil pump to the entire transmission parts. In an auto-controlled transmission, it is run by the sensors, which function uninterruptedly with the transmission control module to control where all the liquids (fluids) are delivered. However, it’s a complex part, indeed the most crucial one in a transmission.


Above we have mentioned the functions of automatic transmission and along with that we also gave you an overview on what are the essential parts of an automatic transmission system.

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