Movement at the pedal pad is transferred through an operating mechanism, to the clutch assembly on the rear of the flywheel.
This mechanism may be mechanical or hydraulic.
Mechanical systems may use a system of levers but cable operation gives more flexibility and is more common.
This is a cable-operated control for a front-wheel drive vehicle.
The outer cable is fixed to the pedal box inside the vehicle and to the clutch housing in the engine compartment. The inner cable connects between the upper end of the clutch pedal and an external lever on top of the clutch housing.
This lever is connected to a vertical shaft, supported in the housing and attached internally to a release fork, which carries the release bearing.
Depressing the pedal relays the movement through the cable, and the release bearing thrusts against the diaphragm fingers on the pressure plate.
An adjustment on the cable, provides for a minimum amount of free-play to be maintained, between the release bearing and the pressure plate fingers, when the pedal is in the released position.
This prevents constant contact of the bearing with the fingers, and subsequent rotation of the bearing, when the engine is running.
A large force is required to depress the pressure plate fingers, so the system gives a mechanical advantage of around 8 to 1. This means the force applied at the pedal pad is magnified 8 times at the release bearing
The corresponding movement ratio can give a pedal movement of up to 200 millimeters, while the release bearing only moves a fraction of this amount.
In hydraulic clutch control, the pedal acts on a master cylinder, connected by a hydraulic pipe and flexible hose, to a slave cylinder, mounted on the clutch housing.
The slave cylinder operates the clutch release fork.
This vehicle uses a centre valve master cylinder.
With the pedal in the off position, the centre valve is clear of the inlet port and fluid can flow to or from the reservoir, into the cylinder.
When the pedal is initially depressed, the piston is moved forward, taking the valve assembly with it. The centre valve closes off the inlet port from the reservoir, trapping fluid in the cylinder bore.
Further piston movement displaces fluid through the outlet port, and into the connecting lines to act on the slave cylinder piston.
The movement of the slave cylinder piston is transferred through a push-rod to the clutch release fork, to operate the clutch.
When the pedal is released, displaced fluid returns to the master cylinder, and the centre valve returns to being slightly clear of the inlet port.
