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Lotus Service Notes Section QH Page 3 QH.1 - GENERAL DESCRIPTION The driving element of the clutch assembly consists of the rear face of the engine flywheel, and a pres- sure plate fixed to the flywheel via the spring diaphragm clutch cover assembly. The driven element, is a single, dry, double sided friction plate, splined to the gearbox input shaft, and interposed between the flywheel and pressure plate. The diaphragm spring in the clutch cover clamps the friction plate between the pressure plate and flywheel to provide the drive connection between engine and gearbox. The gearbox input shaft, on which the friction plate is free to slide axially, is 'overhung' from the gearbox, with no spigot bearing in the rear end of the crankshaft. The hydraulic clutch release mechanism uses a master cylinder fixed to the pedal box, and a slave cylin- der bolted directly to the transmission case. The master cylinder is connected to the fluid reservoir of the brake master cylinder, and uses a steel pipe routed along the outside of the LH chassis side rail to connect with the slave cylinder via a flexible hose. The slave cylinder operates a release fork which pivots on a ball end fulcrum pin and presses the release bearing against the inner ends of the diaphragm spring fingers, which pivot about their fulcrums and relieve the clamping force applied to the pressure plate via the diaphragm outer edge. The release bearing slides on a guide sleeve surrounding the gearbox input shaft. A preload spring inside the slave cylinder applies light pressure to the release lever in order to ensure that contact between the release bearing and diaphragm spring fingers is maintained. No routine adjustment of the clutch or release mechanism is required. The clutch slave cylinder is self adjusting, with the 'rest' position of the piston dependent on the thickness, or degree of wear, of the friction plate. As wear of the friction plate takes place, and its thickness is reduced, the slave cylinder piston is pushed progressively further back on the return stroke with fluid being returned to the master cylinder reservoir. QH.2 - CLUTCH PEDAL The clutch pedal is machined from an aluminium alloy extrusion which is common to the brake and throttle pedals, with an extruded footpad keyed, bonded and rivetted to the bottom of the pedal. Synthetic 'top hat' bushes are used to provide maintenance free articulation on the steel pivot shaft, with a pair of synthetic bearing rings supporting a cylindrical steel trunnion to actuate the master cylinder pushrod. Note that the two synthetic bearing rings may be replaced with the pedal 'in-situ', by using a suitable bolt with clamp washers to press the rings into position. Each bush has an outer diameter chamfer at one end to aid insertion. The master cylinder pushrod is captive in the end of the master cylinder and is screwed fully into the pedal trunnion. With the clutch pedal released, there should be a clearance between the pedal and the pedal box in order to allow the master cylinder to 'top out'. Conversely, the pedal should contact the floor before the cylinder 'bottoms out'. QH.3 - HYDRAULIC RELEASE SYSTEM Master Cylinder The clutch master cylinder is mounted on the pedal box, and is accessible from within the front services compartment. The cylinder is not equipped with its own fluid reservoir, but instead is linked via hose to the adjacent brake fluid reservoir. There is no provision for any servicing of the master cylinder, and if found to be faulty, the unit should be replaced. To replace the master cylinder: - Clean the master cylinder and surrounding area with methylated spirit. Do not use petrol or paraffin. - Take all necessary precautions to guard against contamination of painted surfaces with brake fluid. - Disconnect and immediately plug and cap the hose connection to the fluid reservoir, and the output pipe connection. - From inside the footwell, remove the two bolts securing the cylinder to the pedal box. Withdraw the cylinder from the front services compartment. - To refit, reverse the removal procedure, taking care to feed the pedal pushrod through the dust boot and into the end of the master cylinder as the cylinder is positioned. Tighten the outlet pipe connection to 20 - 24 Nm and bleed the hydraulic system of air. Updated 9th June 2010 |