Lotus 2004 ELISE Service Notes page 410

Lotus Service Notes
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
cylinder 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.
Section QH
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