The pressure plate is normally closed clamping the disc between the pressure plate and the flywheel. When the clutch pedal is depressed the pressure plate is forced open creating a very small space between the disc, flywheel and pressure plate. When the disc moves away from the flywheel, power flow from the engine to the transmission is interrupted. When the clutch is engaged, the disc slips briefly to provide smooth engagement and, then clamps the disc against the flywheel. This causes the input shaft to turn, transmitting power to the transmission.

Disc

The disc hub is splined to fit the input shaft, provides smooth engagement and dampens engine vibrations via torsion springs in the damper assembly. It is mounted to the input shaft between the flywheel and the pressure plate. It can slide forward and backward on the input shaft, but cannot rotate without rotating the transmission input shaft.

Pressure Plate

The pressure plate clamps the disc against the flywheel during engagement. During disengagement it releases pressure on the disc, creating a gap large enough for the disc to move away from the flywheel and enable the driver to shift gears.A typical diaphragm spring clutch consists of a pressure plate, diaphragm spring, pivot ring, drive straps, and a cover. When the release bearing contacts the tips of the diaphragm spring fingers, it moves them toward the flywheel. The outside diameter of the diaphragm spring pivots on the pivot ring inside the cover. This action lifts the pressure plate off the flywheel through the drive straps that connect the cover to the pressure plate.Lever style clutches produce clamp load by pressure from coil springs. As the friction material of the disc wears, the springs expand, reducing their clamping force. At the same time, pedal effort remains high. As a result of these disadvantages, passenger cars and light trucks are now almost exclusively equipped with diaphragm spring clutches.Diaphragm spring clutches maintain higher clamp load than lever style clutches throughout the service life of the clutch. As disc friction material wears, clamp load increases during the first half of clutch life before decreasing gradually to its original level. Diaphragm spring clutches require less pedal effort the further the pedal is actuated, reducing stress on release system components.

Flywheel

Bolted to the end of the crankshaft, the flywheel provides the mounting surface for the clutch. During engagement, the disc is clamped against the flywheel by the pressure plate.In addition to its other functions, the flywheel acts as a heat sink, dissipating heat and moving it away from the clutch pressure plate and disc friction material. The flywheel must provide a smooth, flat surface in order for the clutch to operate properly.

Release Bearing

When depressing the clutch pedal the fork movement causes the release bearing to move along the transmission-bearing retainer forcing the diaphragm spring fingers to open the pressure plate. The internal bearings in the release bearing enable it to turn while applying pressure to the diaphragm spring fingers. The bearing retainer must be parallel to the input shaft and provide a smooth surface for the release bearing to function properly.Angular-contact bearings, found in hydraulic release systems and self-adjusting cable systems, are in constant contact with the diaphragm spring fingers. Self- centering bearings are designed to compensate for slight misalignment between the engine and transmission. It is normal for these bearings to be "off center" until they contact the diaphragm spring fingers.Some vehicle designs utilize a concentric slave cylinder. It eliminates the need for a number of release system components, including the release fork, pivot ball and bearing retainer. They are located inside the bell housing and should replaced when replacing the clutch to avoid rework and additional labor cost.

Pilot Bearing/Bushing

The pilot bearing/bushing supports the end of the transmission input shaft and centers the disc on the flywheel. Types of pilots include conventional ball bearings, needle bearings and sintered bronze bushings.A small and relatively inexpensive component, the pilot bearing or bushing should always be replaced during clutch installation. The variety of problems caused by a worn or defective pilot bearing or bushing are not worth the risk of having to remove the transmission to replace this component later.

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