To replace a worn clutch disc, you must first remove the gearbox - this work requires solid knowledge and the use of special tools and fixtures. Therefore, the replacement of the clutch must be carried out in a car repair shop.
The main elements of the clutch
Flywheel.
Mounted on the end of the crankshaft and bolted to it.
Driven clutch disc.
It moves freely on the splines of the input shaft of the gearbox and is clamped between the flywheel and the pressure plate by the force that the central diaphragm spring creates. Friction linings are riveted on both sides of the driven disk. The clutch disc is connected to the hub through the parts of the torsional vibration damper. The need for a torsional vibration damper is caused by the following.
With a sharp change in the speed of the car, hitting bumps in the road, abrupt engagement of the clutch and due to uneven engine operation, dynamic loads occur in the car transmission, causing twisting (unwinding) transmission shafts. The uneven torque of the engine can cause significant overloads in the transmission due to the occurrence of torsional vibrations and resonance when the frequencies of the transmitted loads coincide with the natural frequencies of the transmission. Elastic vibrations of the transmission lead not only to the appearance of noise in mechanisms and assemblies, but also to dangerous vibrations, and sometimes to breakage of parts, when the vibration amplitude increases significantly. The energy of torsional vibrations is absorbed by the absorber (damper).
The outer diameter of the Ford Fiesta clutch disc is 180 mm (Fiesta 1.8D - 210 mm).
Clutch Release Bearing -
(on all Fiesta models since 1996 built into the clutch slave cylinder). It acts on the pressure plate spring and moves the pressure plate away from the clutch disc. As a result, the clutch disc is released from its clamped position and can rotate freely between the flywheel and the pressure plate, as a result of which the engine and gearbox are separated.
Automatic gap adjustment.
Pic. 12.2. Hydraulic clutch drive: 1 - pre-pressure valve; 2 - reservoir with brake fluid; 3 - fluid supply hose; 4 – the main cylinder of coupling; 5 - pressure pipeline; 6 - clutch slave cylinder combined with clutch release bearing (on all Fiesta vehicles since 1996)
Since 1996, all Fiestas have automatically adjusted the required clutch pedal clearance. If your car's clutch begins to slip, then you need to replace the clutch disc or check the operation of the hydraulic clutch pre-pressure valve (pic. 12.2).
TECHNICAL DICTIONARY
Clutch operation
Clutch gap.
As long as the clutch pedal is not depressed, the clutch release bearing is located at a certain distance from the pressure plate diaphragm spring. With an increase in vehicle mileage, the clutch clearance, by analogy with the wear of the clutch disc, becomes smaller: the diaphragm spring approaches the clutch release bearing. As soon as the bearing touches the diaphragm spring without play, the pressing force of the pressure plate is reduced, which automatically reduces the friction force between the surfaces of the clutch disc, flywheel and clutch pressure plate. If the gap is not adjusted, the clutch no longer transmits torque from the engine to the gearbox without slipping - the clutch slips.
Clutch disengagement.
When the clutch pedal is pressed, the piston moves in the clutch master cylinder and compresses the fluid, which enters the clutch slave cylinder through the hose. Under pressure, the piston extends from the clutch slave cylinder and moves the bearing, which acts on the pressure plate spring and moves the pressure plate away from the clutch driven plate. As a result, the clutch disc is released from its clamped position and can rotate freely between the flywheel and the pressure plate, as a result of which the engine and gearbox are separated.
Clutch engagement.
When the clutch pedal is released, the diaphragm spring again presses the pressure plate against the flywheel, and all clutch parts form a strong, force-locked connection - torque is transmitted from the engine to the gearbox.
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