Is the transmission part of the engine? [Complete guide]

The engine and transmission are bolted together to form a single unit. But some people wrongly consider this assembly as the engine itself and transmission as a part of the engine.

Transmission and engine are separate units on the vehicle. Both are connected together by the clutch or torque converter. Engine converts fuel energy into mechanical power while the transmission converts the engine power output into different sets of speeds and torque necessary for different driving conditions.

engine of the car separated

It is better to know how transmission is different from the engine, how they are connected together and what is the role of each component.

Is the transmission part of the engine?

The transmission and engine are different units and performs different role to propel the vehicle. The engine is like a powerhouse that creates mechanical power.

While transmission helps to serve the power in different combinations of torque and speed based on the driving situation.

In the case of a motorcycle, you can easily distinguish between the engine and transmission.

transmission and engine in motorcycle

The engine output is connected to the transmission by means of a clutch or torque converter and therefore both units rotate separately when the clutch is in disengaged condition.

Both components are different from each other with their own functions and hence we can say that transmission is not part of an engine but both are necessary to run your car on pavement.

What connects transmission to the engine?

The engine never stops revolving even when the vehicle is stationary. but it would become impossible if the engine output gets directly coupled to the transmission. Every time you would have to switch off the engine to stop the vehicle.

Following are the different types of devices that are mounted between the engine and transmission. While running it connects the engine and transmission and disconnects when the engine is idling.

Visualization of assembly of engine and transmission
Credit: EricTheCarGuy

1] Clutch:

It is the mechanical device, that engages and disengages the engine to the transmission. This device requires manual control for engagement and disengagement.

The mechanical clutch is normally in an engaged condition. When we press a clutch pedal, it cut-off the power transmitted to the transmission.

If you want more detail about clutches, read our detailed article on different types of clutches.

2] Torque converter:

The torque converter is a type of fluid coupling, that consists of an impeller, turbine, stator, and housing. The impeller is connected to the engine output and rotates as the engine rotates.

The turbine is connected to the transmission and the housing is filled with fluid.

As the engine rotates, the impeller pushes the liquid in the outside direction. This directed fluid passed over a turbine, causing the turbine to rotate.

At lower speeds, the impeller is unable to rotate the turbine, thus the vehicle remains stationary with the engine idling.

But as the driver presses the gas pedal, the impeller speed increases causing the turbine to rotate. Hence vehicle starts to move on the road.

What is the role of transmission?

The output torque of the engine rises along with the output speed of the engine. It means that the engine gives lower torque at a lower speed while it gives higher torque at a higher speed.

The vehicle requires different torque and speed combinations and the transmission helps to convert the output of the engine into the various torque and speed combinations/steps.

Purpose of transmission in vehicle

It has different gear ratios that are generated by meshing different sizes of gears (in the case of sliding mesh) or by clutching different constantly meshed gear sets to the output shafts (in constant mesh).

Other than gears, the transmission system is also made up of a CVT pulley and belt in the continuously varying transmission.

In this system, pulleys are mounted on the crankshaft and output shaft. The diameter of the belt over the pulleys varies as per the engine speed therefore by varying the diameter of input and output pulleys the transmission can attend an infinite number of gear ratios.

Therefore the conversion of the engine output into the required output is the main function of the transmission.

What does the engine do in a car?

The engine is the heart of any automobile that helps to move the vehicle on road and also helps to power the various accessories.

The main function of the engine is to convert the chemical energy of various fuels into the mechanical energy of the crankshaft.

The mixture of air and fuel is burnt into the combustion chamber made by the piston and cylinder. It results in a sudden increase in temperature and pressure inside the cavity.

This pressure helps to actuate the piston inside of the cylinder. Thus the piston starts to move continuously in reciprocating motion and that motion is further converted into rotary motion by using the connecting rod, crank, and crankshaft.

Final words:

The engine and transmission work together when they are engaged and work individually during disengagement. If you want to know how the engine differs from the transmission, read out our this article.


  1. Are the engine and transmission the same?

    The engine and transmission are different components connected together by a clutch.

  2. Can the engine run without the transmission?

    The engine can run without connecting it to the transmission.

Pratik is a Graduated Mechanical engineer. He enjoys sharing the engineering knowledge learned by him with people.

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