Often referred to as being the same thing, flywheels and flexplates have similarities but are indeed quite different.
First, here are some of their similarities:
- Both are circular in nature and are mounted to the engine crankshaft.
- Both have a toothed ring gear that engages with the starter.
- Both serve as the link that marries the transmission to the engine
- Both can help balance the engine while it’s in operation.
Flywheels are typically found on vehicles equipped with manual transmissions, while flexplates are used in vehicles with automatic transmissions.
A manual transmission has a flywheel that is attached to the crankshaft and has a clutch disk in between the pressure plate and flywheel. When the clutch pedal is depressed, the throw out bearing is pushed in, which forces the pressure plate to stop applying pressure to the clutch disk. As this happens, it stops receiving power from the engine, so the gear can be shifted without damaging the transmission. Once the operator/driver shifts into a new gear, the clutch pedal is released then the clutch disk is allowed to start receiving power from the engine once again.
Automatic transmissions eliminate the clutch and grinding, basically automating the shifting process so the driver does not have to worry about shifting gears while driving. A flexplate is mounted to the crankshaft and connects the output from the engine to the input of a torque converter.
Torque converters replace the clutch of a manual transmission, allowing the load to be separated from the power source. They are generally a type of fluid coupling that can multiply torque and is used in transferring rotating power from the prime mover (internal combustion engine or electric motor) to a rotating driven load. The torque converter is located between the flexplate and the transmission.
Flywheels, due to the friction process, are very thick, made of steel and are as heavy as they look. Their lifecycle can outlast that of the clutch, but will need resurfacing before installing a new clutch. When they need do need replacing, you can typically get away with using an aftermarket replacement.
Flexplates are much thinner than a flywheel, as well as the ring gear it uses to connect with the starter (depending on vehicle and engine size), and are much, much lighter. This is due to the fluid coupling of the torque converter, which eliminates the grinding of a clutch. The lighter, thinner metal frame has an ability to flex across its main axis – bending side to side (hence the name Flexplate) – taking up motion in the torque converter as the rotational speeds change.
The metal frame of the flexplate itself will have multiple machine-cut holes within the body of the plate. One set of holes will look uniform and would be for mounting to the crankshaft. The other holes are specific to the vehicle, torque converter set-up and potential weight balance of the flexplate.
No matter the car size, small economy size or heavy duty truck, if your vehicle has a manual transmission and you have to step on the clutch to shift gears, your vehicle has a flywheel as part of your transmission. If all you have to do is put the shifter in drive (D) and step on the gas pedal, your vehicle has a flexplate.
What do you have in your ride?