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Do Automatic Transmissions Have a Flywheel?

Side view of an automatic transmission with the gears visible inside

Flywheels are an important part of any manual transmission vehicle that stores energy before releasing it as needed. As such, people think they are exclusive to manual transmission systems. This perception can lead to confusion when they move to an automatic transmission, causing many to wonder if these systems have flywheels as well.

While automatic transmissions do have flywheels, they are usually not traditional ones. Instead, they have flexplates. Flexplates serve the same function as flywheels but without direct input from the driver. As a result, it is these plates that make automatic transmissions automatic.

This automatic operation can make automatic transmission vehicles more complicated to understand and troubleshoot. As a result, by reading further, you will learn how flexplates work, so you will know when you should take your vehicle in for repairs or if you can do it yourself.

Do Automatic Cars Have Flywheels?

A transmission flywheel is a relatively large, fast-rotating cast iron, steel, or aluminum disc with a steel insert. It serves as the interface between the clutch mechanism and the drive train. As such, it provides the torque and horsepower required to move the vehicle.

Flywheels do this by storing excess fuel energy until the clutch releases it by slowing the wheel down. This feature gives the driver full control of the vehicle’s motion while improving its fuel economy and performance. As such, most people typically consider them parts of manual transmission systems.

Automatic vehicles do not require their drivers to manually shift gears, making them simpler to operate. As a result, they have no manual controls and use automatic gear changes instead. Because of this, many automatic vehicles do not have a dedicated flywheel. Instead, they use some sort of flexplate.

Automatic transmission with the gears visible inside isolated against a white background

Automatic Transmissions Use Flexplates

Flexplates serve the same function as flywheels but without the connection to the driver or automation process. They can also take multiple forms depending on their underlying technologies with the following as the most common designs:

  • Electromagnetic clutch
  • Hydraulic pumps
  • A mechanical disc – only used in racing vehicles

In either case, these flexplates are significantly smaller than their mechanical manual transmission counterparts. They also use non-mechanical means to operate and transfer power usually in the form of either hydraulic or electric torque converters. As such, flexplates mostly exist as mounting points for the converters and starting mechanisms.

Although, some heavy-duty automatic transmission applications do require a true flywheel. For instance, racing cars use specially designed flexplates that can interface with special small-diameter clutch assemblies. This lets them enjoy high acceleration rates.

The other common uses for true automatic transmission flywheels are farm vehicles and semi-tractors. These vehicles require an extra-heavy flywheel to pull heavy loads over rough terrain.

ATP Z-269 Automatic Transmission flexplate flex plate isolated against a white background
ATP Z-269 Automatic Transmission Flex-Plate

Flywheels Also Start Engines

Along with maintaining smooth driving conditions, a vehicle’s flywheel is also its chief starting mechanism. This is because the flywheel also has a direct connection to the starting ring gear. This gear encompasses the flywheel and uses electricity to spin. This gear presses into the flywheel when you start the vehicle, causing the flywheel to spin.

Illustration of how the flexplate flywheel crankshaft camshaft and timing chain all work together isolated against a white background

How Flywheels and Flexplates Work

Flywheels make vehicles easier to operate, making them integral parts of the transmission system. Their primary purpose is to store energy which the engine can redirect to move the vehicle forward or backward as needed. They also serve the following functions in a manual transmission:

  • Store and Redirect Energy as Needed – maintain and regulate the vehicle’s speed, ensuring smooth and consistent acceleration. They also provided the extra power the vehicle needs to start or climb up a hill.
  • Ensures Smooth Vehicle Operation – smooths out the power generation and distribution preventing stalls. Fuel combustion has incredibly inconsistent output. Directing it through the flywheel reduces vibrations and fluctuations.
  • Enhanced Ride Quality and Performance – makes the entire vehicle easier and safer to control. It will respond to the driver’s command intuitively.

Flywheels provide these functions by storing energy in their rotation and inertia, which is why they are normally so heavy. As such, you will only see lightweight flywheels in high-performance engines which mainly use the flywheel for faster acceleration and deceleration. Regardless of the form, you want your vehicle’s flywheel securely attached to the crankshaft with very strong bolts to prevent shearing.

Automatic transmission flexplate or flywheel visible while still mounted on the car

Flywheels in Automatic Transmissions

Flexplates works slightly differently in automatic transmission system than flywheels do in manual ones. As such, they also serve a slightly different purpose. Automatic vehicles rarely need a flywheel to operate as they already use a 4-cycle engine design. However, they need something to provide the extra power to accelerate and remain fuel efficient.

How Flywheels Transfer Power Through the Engine

With that said, flywheels and flexplates work similarly in both types of transmissions. The only major differences between the two are how they spin and what makes them spin. Either way, their operations follow the following basic steps.

  1. The crankshaft, which is attached to the flywheel makes it spin in a circular motion.
  2. Pressing the accelerator sends power through the driveshaft.
  3. This power makes the gears spin which passes the power between each other until it reaches the flywheel.
  4. The flywheel uses centrifugal forces of a nearby large, fast-rotating gear to combine and transfer the energy into momentum along its rim.
  5. The momentum transfer creates kinetic energy in the drivetrain, sending the power to the wheels.
  6. If there is a disruption in the power flow to the flywheel, it will reduce its momentum to maintain the power output to the wheels.  
3D rendering of a vehicle's undercarriage with the engine transmission wheels and driveshaft visible isolated against a white background

Signs of a Bad Flywheel in Manual and Automatic Transmissions

Like any other part of your vehicle, the flywheel will age and break eventually. Fortunately, numerous signs will develop before it goes bad, giving you time to raise the funds to fix it before it is too late.

The more common signs are:

  • The gearbox gets stuck in neutral or slips when shifting gears.
  • The clutch makes a rattling noise when you depress or release the pedal.
  • The engine vibrates regularly while driving
  • The clutch gives off a burning smell.
  • Your vehicle makes strange noises when starting.

Luckily, these are mostly issues for manual transmission vehicles. Flexplates are normally studier than flywheels and are usually under much less stress. However, they can produce similar effects at the end of their lives as well.

An automatic transmission gearbox of a used car at an auto repair shop getting repaired sitting on a work bench

Conclusion

Flywheels help regulate the power distribution through a vehicle’s engine, making them a crucial component of the operation of the vehicle. However, most automatic transmission systems do not have a traditional flywheel. Instead, they use flexplates and tour converters to reap their higher performance characteristics.

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References:

Car Phrases

Rx mechanic

Car News Cast

Wiki Motors

What is a Transmission Flywheel?

Car Bike Tech

What Is An Automatic Transmission & How Does It Work?

Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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