What is the name of the clutch system in a manual transmission that uses a diaphragm spring?

The clutch system that uses a diaphragm spring is called a diaphragm clutch. In this design, a conical spring-steel plate supplies the clamping force that presses the clutch disc against the flywheel.

The diaphragm spring has radial fingers near its center. When the clutch pedal is released, the spring’s outer section pushes the pressure plate against the disc, allowing engine torque to reach the transmission. Pressing the pedal moves a release bearing against the spring fingers, causing the spring to pivot and relieve pressure on the disc.

Diaphragm clutches became widely used in automotive manual transmissions because they can provide a relatively light and consistent pedal effort. They also compensate more naturally for clutch-disc wear than many older coil-spring arrangements. “Friction clutch” is broader: a diaphragm clutch is usually a type of dry friction clutch, but not every friction clutch uses a diaphragm spring. Hydraulic clutch refers to the actuation method, not the spring design.