The purpose of the clutch is to disconnect and connect engine power at the transmission. A vehicle at rest requires engine torque to get all that weight moving. An internal combustion engine develops torque through engine RPM. It must be allowed to operate without any load until it builds up enough torque to move the vehicle. The clutch allows the transfer of torque over an extended time by slippage of the clutch disc. As the clutch pedal is released more torque is transferred until the clutch is fully engaged. Transferring all of the torque immediately would cause driveline components to wear out or break prematurely. When the pedal is pushed in, the disc and plate separate (the clutch is disengaged) disconnecting the engine from the transmission.
Clutch assemblies include a flywheel, friction disc, pressure-plate, throw out bearing and fork, actuating linkage, and the pedal. The flywheel and pressure-plate are connected to the engine crankshaft. The clutch disc is located between the flywheel and pressure plate; it is splined to the transmission shaft.
Pushing in the clutch pedal actuates the attached linkage. Connected to the other end of this is the throw out fork, which holds the throw out bearing. When the clutch pedal is depressed, the clutch linkage pushes the fork and bearing forward to contact the springs of the pressure plate. This action separates the disc from the plate, disengaging the clutch and allowing the transmission to be shifted into another gear. A clutch return-spring attached to the clutch-pedal permits full release. When you release the pedal, the throw out bearing pulls away from the pressure plate and disengaging the transmission from the engine.
As the pedal is released the pressure-plate makes contact with the friction disc. As the friction disc and pressure-plate move closer together friction between the two increases and slippage is reduced until, when the pedal is fully released the speed of the friction disc and pressure-plate become equal. This stops all slippage, creating a direct connection between the pressure-plate and friction disc. The result is the transfer of power from the engine to the transmission.
The clutch is operating properly if: