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Anatomy of your car's clutch

Anatomy of your car's clutch

The clutch's job is to connect the engine to the gearbox to transfer the rotational motion of the engine to the gearbox (and ultimately to the wheels).

When the clutch is engaged (clutch pedal up) the engine and gearbox are connected, and when the clutch is disengaged (clutch pedal down) the engine and gearbox are separated, and the engine can spin without the car moving.

01 Flywheel

The flywheel is permanently bolted to the engine's crank – and whenever the engine is rotating, so is the flywheel. The teeth around the edge (gear ring) engage with a pinion on the starter motor, which is how the car starts (the starter spins the flywheel using power from the battery until the engine takes over and runs on fuel).

02 Friction Surface

The face of the flywheel is a friction surface which the clutch plate acts against.

03 Clutch Plate

The clutch plate is made up of disc with high friction material around its perimeter. The friction surfaces are on both sides of the disc, with one side acting against the face of the flywheel, and the other acting on the pressure plate.

04 Clutch Plate Springs

The springs mounted on the inner hub of the clutch plate cushion the clutch engagement. They work as a torsional vibration damper to absorb fluctuations in the engine's power delivery. As the springs work as dampers the power delivery is smoother and more linear than if there were no springs. 

05 Splined Hub

The splines at the centre of the clutch plate mate with the splines on the end of the input shaft. The input shaft (not pictured) then transfers the rotational motion of the clutch to the gearbox. With the clutch pedal depressed the clutch plate is disengaged and the input shaft does not spin. But with the clutch engaged the input shaft will spin at the same rpm as the flywheel.

06 Pressure Plate

The pressure plate is bolted to the flywheel – and so spins when the flywheel spin. The clutch plate is sandwiched between it and the flywheel, but is not physically connected to pressure plate. In effect the pressure plate is a spring loaded clamp – designed to clamp down on the clutch plate when the clutch is engaged.

07 Diaphragm Spring

The diaphragm spring is made up of the 'fingers' at the centre of the pressure plate. With the clutch engaged they force the pressure plate onto the clutch plate, and the clutch plate onto the flywheel. With the clutch disengaged they allow the clutch plate to separate from the flywheel.

08 Release bearing

When you press the clutch pedal this acts on a release fork (not pictured) which pushes the release bearing into the diaphragm spring. As the diaphragm is rotating (as it's connected to the pressure plate, which is connected to the flywheel) the release bearing's job is to absorb the rotary motion of the spring fingers against the linear motion of the release fork.