What Is A Transmission In A Car?

Dustin Hawley | Dec 21, 2020

The automobile comprises many parts, and the modern internal combustion engine only works as beautifully as it does due to a synchronized and complex array of components. One of the most critical pieces in a typical car engine is the transmission. Let’s break down what a transmission is and what it does each time you press down on the accelerator.

What does a car transmission do

Car Transmission: An Overview

Put simply, a car transmission is a vehicle’s gearbox. It’s roughly analogous to the gear shifter and chain system that bicycles use.

These components are always mounted straight on the engine so that their attached belt and gear system can effectively convert the combustion power produced by the engine into physical momentum.

Recall how a car engine operates:

  • Fuel (gasoline) is ignited in the combustion chamber of your vehicle’s engine.
  • As fuel ignites, the expanding gas and heat from the miniature explosion push an array of pistons inside your engine’s cylinders.
  • As the pistons are pushed, they move up and down and spin your engine’s crankshaft. 
  • The crankshaft then turns your car’s drive wheels. Through this mechanism, explosive energy is turned into mechanical energy.

So, where does the transmission come into play? In a vacuum (without a transmission), the explosive power produced by a typical automobile internal combustion engine would simply be too high for starting or stopping your car or if you needed to drive around relatively slowly.

A typical car transmission is comprised of between five and six gear sets and a series of gear trains (essentially belts or chains that run along the outside of two or more gears) – that allows a driver to control how much power is delivered to the car without changing how fast the engine runs. 

Put another way, a car transmission helps to ensure that your engine spins at the right rate without going too fast or too slow for your needs. It also ensures that your wheels get the correct amount of power. Without a transmission, any automobile would be difficult to start and stop and would be utterly unreliable.

What Does a Transmission Do?

Transmissions are necessary for any motor vehicle in order to prevent the engine from destroying itself. Without a gearbox system, car engines would turn too quickly for structural stability, meaning most engines would shake themselves to pieces or overheat. Furthermore, any car without a transmission would be unable to harness the engine’s speed, capping its maximum velocity.

A transmission changes gears depending on car speed and accelerator input (i.e., how far down you push the pedal of your car) so that the engine’s RPM or “revolutions per minute” are kept appropriately low. This provides two benefits:

  • Fuel consumption is decreased.
  • The turning gears do not overload your engine.

Additionally, a transmission allows you to harness your vehicle’s engine energy when necessary. When you’re driving slowly, you can stay in a lower gear and avoid damaging your engine. When you must move more quickly, you can switch gears to a higher level. By doing so, the transmission allows you to benefit from more of your car's power, rotating the wheels more quickly.

Manual vs. Automatic Transmission

Modern car transmissions come in two types: manual and automatic.

Manual transmissions are not as standard in modern vehicles since automatic transmissions work precisely the same way but have a lower error rate. Since drivers are not required to change gears as they change speeds or adjust to road conditions, they can focus on driving alone, and machines change gears automatically and smoothly.

How Does a Car Transmission Work?

Regardless of whether your vehicle has a manual or automatic transmission, all car gearboxes work in essentially the same way. The only difference is whether the driver must manually push the clutch to disconnect the engine and transmission and move the car into a new gear level.

  • A gear lever selects and moves gears to connect with one another. The driver operates the gear lever using the clutch control/pedal (if manual). Otherwise, this is performed automatically.
  • When engaged, a clutch or gear lever maneuvers “collar” plates (also called clutch plates) into place to connect to larger gears, which are themselves connected to your car’s differential.
  • As the gear lever moves, different gears may be connected at different times. This alters which sets of gears turn and the power ratio delivered from the engine to wheels.

Ever wondered why your car’s engine might make a horrible sound if you engage the clutch incorrectly? It’s not because the gear teeth are mismatched, as is commonly believed.

In modern transmissions, gear teeth are positioned to be fully engaged at all times – even gears that aren’t technically in play (a state called “freewheeling”).

Instead, that awful grinding sound occurs when the collar plate’s “dog teeth” (connecting notches) don’t match up with the right holes in the side of a transmission gear.

Manual Transmission

With a manual transmission, the clutch must be engaged such that the collar plate disconnects fully from transmission gears. This is why when engaging a manual transmission and making a change from one gear to another, a car might seem to lag or jump.

The clutch must then be maneuvered so that the collar plate lines up perfectly with the transmission gears you want to select. If done correctly, your car will immediately begin to drive at your selected gear.

Automatic Transmission

An automatic transmission also features an automatic clutch. Instead of relying on human control, built-in sensors, processors, and actuators operate the clutch at the perfect moment based on your current speed, accelerator pressure, and other factors. This allows drivers to focus on other tasks on the road.

You can actually hear an automatic transmission operate as you drive a vehicle equipped with one. As you push down on the accelerator, your engine will become louder, and its built-in torque converter will sense the change and automatically shift to a higher gear. 

In contrast, a car with a manual transmission will begin to slow and struggle as it is pushed to higher speeds until you switch gears.


Ultimately, car transmissions are just one part of the fascinating and complex process that occurs every time you start your engine to go for a ride. For more information and helpful guides regarding all things automotive, visit us at jdpower.com.

Explore new car previews
2023 Ram 2500 Heavy Duty Rebel Preview
2023 Ram 2500 Heavy Duty Rebel Preview
Ram used the 2022 State Fair of Texas to show off its new 2500 Heavy Duty Rebel, a beefy off-road truck that retains its work-truck capabilities. It brings hardcore off-road upgrades such as an electronic-locking rear differential and a rear limited-slip differential.
Read the full review
2023 Ford F-Series Super Duty Preview
2023 Ford F-Series Super Duty Preview
F-Series Super Duty trucks got what they needed for the 2023 model year. Ford announced a more powerful line of heavy-duty trucks with a load of available new tech, great standard safety features, and unique upfits to make the trucks more appropriate for specific industries.
Read the full review
2023 BMW XM Preview
2023 BMW XM Preview
The XM is BMW’s sendoff to performance gas SUVs, and it features a unique plug-in hybrid (PHEV) powertrain with incredible power and acceleration.
Read the full review
Read all articles

Scroll to the top
New Car Preview
2023 Mercedes-Benz EQE Preview
Most Dependable
2019 Vehicle Dependability: Most Dependable Luxury Coupes and Convertibles
Most Popular
10 Most Popular Small Cars
New Model Update
New for 2019: GMC
New Car Preview
2023 Toyota Crown Preview
More related