The purpose of the clutch is to disconnect and connect engine power at the transmission. A car at rest requires a lot of engine torque to get all that weight moving. An internal combustion engine does not develop a high starting torque (unlike steam engines), so it must be allowed to operate without any load until it builds up enough torque to move the car. Torque increases with engine rpm. The clutch allows the engine to build up torque by physically disconnecting the engine from the transmission, relieving the engine of any load or resistance. The transfer of engine power to the transmission (the load) must be smooth and gradual; if it weren't, drive line components would wear out or break quickly. This gradual power transfer is made possible by gradually releasing the clutch pedal. The clutch disc and pressure plate are the connecting link between the engine and transmission. When the clutch pedal is released, the disc and plate contact each other (clutch engagement), physically joining the engine and transmission. When the pedal is pushed in, the disc and plate separate (the clutch is disengaged), disconnecting the engine from the transmission.
The Probe clutch is a single plate, dry friction disc with a diaphragm-style spring pressure plate. The clutch disc has a splined hub which attaches the disc to the input shaft. The disc has friction material where it contacts the flywheel and pressure plate. Torsion springs on the disc help absorb engine torque pulses. The pressure plate applies pressure to the clutch disc, holding it tight against the surface of the flywheel. The diaphragm spring is located between two fulcrum rings riveted to the clutch cover. The clutch operating mechanism consists of a release bearing, fork and cylinder. The release fork and slave cylinder transfer pedal motion to the release bearing. In the engaged position, the diaphragm spring holds the pressure plate against the clutch disc, so engine torque is transmitted to the input shaft. When the clutch pedal is depressed, the release bearing pushes the diaphragm spring center toward the flywheel. The diaphragm spring pivots the fulcrum, relieving the load on the pressure plate. Steel spring straps riveted to the clutch cover lift the pressure plate from the clutch disc, disengaging the engine drive from the transaxle and enabling the gears to be changed.
The hydraulic clutch control system consists of a fluid reservoir, master cylinder, slave cylinder and pressure line. The clutch master cylinder and reservoir are mounted on the firewall (bulkhead). Fluid level is checked at the reservoir.
The clutch master cylinder converts mechanical clutch pedal movement into hydraulic fluid movement. The fluid pressure is transmitted down the pressure line to the slave cylinder. The slave cylinder is mounted on the transaxle. It converts the hydraulic fluid movement to mechanical movement, allowing the release fork and bearing to engage and disengage the clutch.