Figure 7-2.Friction disk clutch with flexible center.
It also contains a spring arrangement and a pressure
plate (fig. 7-3) for pressing the disk tightly against the
face of the flywheel. The friction disk is splined to the
clutch shaft. The splines consist of two sets of teeth: an
internal set on the hub of the friction disk and a matching
external set on the clutch shaft. They permit the friction
disk to slide back and forth along the shaft but force the
disk and the shaft to rotate together.
The flywheel, attached to the end of the engine
crankshaft, rotates when the engine is running. When
the clutch is engaged in the coupling position, the
friction disk is held tightly against the flywheel by the
pressure plate springs, so that it rotates with the
flywheel. This rotary motion is carried through the
friction disk and clutch shaft to the transmission.
To disengage (or uncouple) the clutch, the clutch
operator presses the clutch pedal down. This causes the
clutch fork to pivot so the clutch release bearing is forced
inward. As the release bearing is moved inward, it
operates the pressure plate release levers (fig. 7-4). The
release levers take up the spring pressure and lift the
pressure plate away from the friction disk. The friction
disk is no longer pressed against the flywheel face, and
the engine can run independently of the power train.
Releasing the clutch pedal permits the clutch fork to
disengage the release bearing, so the springs will again
cause the pressure plate to force the friction disk against
the flywheel face to rotate together.
There are two types of clutch operating systems:
mechanical and hydraulic. The mechanical system is the
most common and uses a rod type of linkage (fig. 7-5);
Figure 7-3.Pressure plate and related parts.