Clutch system description (page 2 of 2)

The operating face of the flywheel is machined to provide a smooth surface for the drive plate to engage on. Three dowels are fitted to the outer diameter of the flywheel and provide for the location of the pressure plate. Six threaded holes provide for the attachment of the pressure plate. The flywheel is balanced to ensure that it does not produce vibration when rotating.

The pressure plate comprises a diaphragm, pressure plate and cover. The pressure plate is mounted on and rotates with the flywheel. Three dowels locate the cover and six bolts secure it to the flywheel. The same 228 mm (9.0 in) diameter plate is used on K and L Series engines.

The pressure plate is forged from cast iron and machined to provide a smooth surface for the drive plate to engage on. Three lugs on the outer diameter of the pressure plate connect it via three leaf springs to the cover. The leaf springs have three tempered steel leaves and pull the pressure plate away from the drive plate when the clutch pedal is depressed. The cover is made from pressed steel.

The diaphragm comprises a cast ring with eighteen fingers on its inner diameter. Two circular steel fulcrum rings are attached to the housing and allows the diaphragm to pivot between them. The diaphragm is not physically attached to the pressure plate. When pressure is applied to the diaphragm fingers from the release bearing, the diaphragm pivots between the fulcrum rings and moves away from the pressure plate. The leaf springs attaching the pressure plate to the cover move the plate away from the drive plate.

The drive plate is sandwiched between the flywheel and the pressure plate. The drive plate has a splined hub which engages with the splines on the primary shaft from the gearbox. The splined hub is located in an inner plate which contains four compression pre-damper springs. The inner plate is retained by the springs which can compress in both directions to cushion engine vibration at tickover. The inner plate is located on eight larger compression springs which are located in a central plate. The hub is sandwiched between the central plate and the friction damper. The friction damper comprises friction washers located between the hub and the central plate. The friction washers reduce transmission noises and vibrations.

The drive from the inner plate is transferred to the central plate through the larger compression springs. Two outer plates are located either side of the central plate. The central plate is connected to the outer plate in slots and retained with rivets. The slots allow the central plate to move and compress the springs absorbing shock loads when the clutch is engaged or when the engine is decelerating. One of the outer plates is marked ’flywheel side’. This outer plate must face the flywheel when installed.

One of the outer plates has a spring steel plate riveted to it. The plate provides the attachment surface for the clutch drive plate friction material which is riveted to each side of the plate.

The facing material comprises two discs which are riveted to each side of the spring steel plate. The rivets are secured through recessed holes in the facing material and emerge in clearance holes in the opposite disk.

The drive plates used K and L Series engines are both of the compound centre type. The compound centre drive plate allows angular movement of the hub at low torque levels. The K Series drive plate is 215 mm (8.5 in) diameter and has a facing material manufactured from Raybestos K202. The L Series drive plate is 228 mm (9.0 in) diameter and has a facing material manufactured from APTEC T385.