I understand how a clutch can separate the flywheel from the clutch disk so that power is disconnected from the engine.

When that happens, does the input shaft (along with the countershaft) stop immediately?

If they are moving, they should have some rotational energy, how is all the energy lost in one second and it stops?

2 Answers 2


A basic clutch is made up of three major parts:

  • Flywheel

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  • Friction disk

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  • Pressure plate

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(NOTE: These three pieces do not actually go together. I'm using the pictures for illustrative purposes.)

The flywheel is attached to the back of the engine. The pressure plate is attached to the flywheel. Sandwiched in between the two is the friction disk. The friction works a lot like brake pads, in that it grips the flywheel/pressure plate on either side through, what else, friction.

enter image description here

The splined input shaft of the transmission is placed through the friction disk and rides on a pilot bearing at the center of the flywheel. When you press the clutch pedal, the the throwout bearing is pushed against the clutch fingers, which pulls the plate away from the flywheel. When the pressure plate is pulled away, it allows for enough space between the to for a decoupling and the friction disk is allowed to spin freely. This disconnects the power output of the engine from going to the transmission. When you release the clutch pedal, the plate moves back towards the flywheel, recapturing the friction disk and power is restored to the transmission.

Please not, it's not that the input shaft stops immediately when the clutch is disengaged. It's just that each entity (engine and transmission) are allowed to operate independently of each other at that point. This gives you time to change gears or prepare for a stop.

  • What is the difference between a friction disk and a clutch disk, or are they the same thing? Jan 12, 2016 at 13:49
  • 1
    @MaxGoodridge - Same thing. Friction disk is the more common name as far as I know. Calling it a friction disk is a little more descriptive of what it actually does. Nov 22, 2016 at 2:14

What is a clutch?

A Clutch is a simple device though not exclusive to auto mobiles which allow two gears/shafts of different speed to be synchronized in a smooth manner.

In vehicles, the clutch is used to connect/disconnect the transmission and the crankshaft.

What does it do?

Basically the clutch acts like a brake for the engine that is why improper shifting can cause your car or bike to stall, the clutch slows down the engine so that the wheels can catch up.(very rudimentary explanation)

What are the parts?

enter image description here

The above diagram shows the basic form of most clutches.

The clutch has these three parts sandwiched together creating friction and syncing the engine and the wheels(through gearbox).

  • The flywheel

To represent the engine we have the flywheel which is attached to the crank and it moves with the engine.The clutch disc

  • The clutch disc

Between the flywheel and the pressure plate is the clutch disc. The clutch disc has friction surfaces similar to a brake pad on both sides that make or break contact with the metal flywheel and pressure plate surfaces, allowing for smooth engagement and disengagement.

  • The Pressure Plate

When the clutch pedal is depressed, the pressure plate releases, allowing itself and the flywheel to spin independent of the disc, which prevents torque from being transmitted from the engine to the gearbox. Generally made of cast iron or steel, the pressure plate uses a diaphragm-type spring to apply force against the disc once engaged, which is fastened to the assembly by a series of straps.

  • Throw out Bearings

The throwout bearing sits against the pressure plate in either a push-style or pull-style arrangement that compresses the diaphragm and releases the disc when the clutch pedal is depressed. Once force is applied, the diaphragm releases tension, allowing the disc to spin independent of the assembly.

The below two images will show how clutch works when engaged and disengaged.

  • Disengaged

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  • Engaged

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  • Types of clutch

There are two types of clutches in the bike world DRY and WET/Oil bathed.

The Wet clutch is where the entire assembly is immersed in engine oil and is lubricated by it, due to viscosity of the oil , some power loss can be attributed to this approach but they significantly improve the life of the clutch and reduce sound.

The dry clutch as the name suggests does not have anything between the whole mechanism , it is much better at transferring the power since there is no 3rd party material restricting it but , they are loud and create a rattling sound and life of the clutch is low compared to wet setup( most Ducati are known for having dry clutches and is one of the defining sounds of a Ducati)

  • Slipper clutch

In motorbikes engine braking can cause the rear wheel to lock up , this kind of slipper clutch will just slip over the gear and will not engage it unless rpms are matched, mostly a safety feature.

  • What can I do to improve performance

Simply adding additional clutch plates will make the system engage much faster and more efficiently ( coming close to dry clutch setup) the problem is that the outer pads will wear out a bit faster.

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