The Rolls-Royce clutch

The clutch used by Rolls-Royce on the Silver Ghost was a traditional cone clutch, fitted with a fabric lining and effectively running in oil. With the advent of the Phantom 1 and 20hp chassis a plate clutch was specified. The basic design of this was common with a number of other contemporary motorcars.

In this design the clutch driven plate is a thin steel disc about 2.5mm thick, mounted on a splined hub on the gearbox shaft. It does not carry the clutch linings. Instead the linings are mounted either side of the driven plate. They are fitted to the face of the flywheel in front of the driven plate and the face of the spring-loaded pressure plate behind. Any slipping of the clutch occurs between the faces of the steel plate and the linings. The consequence of this is that heat generated between the linings and the driven plate has nowhere to go except in to the thin plate - the linings are not efficient conductors of heat. As a result the surface of the steel driven plate can become very hot if the clutch is allowed to slip for any length of time, and this will have a damaging effect on the linings.

Modern cars, with engine idling speeds often around 1000 rpm or more, and which have little or no power below 1500 rpm, require the clutch to be slipped to get moving. With the pre-war Rolls-Royce fitted with the Rolls-Royce clutch, including the Bentley 3 1/2L, slipping the clutch must be kept to an absolute minimum otherwise the life of the clutch will be severely curtailed. Because there is so much torque at low engine speeds it is possible to engage the clutch very quickly without any significant increase in engine speed to get the car moving from stationary. This can be done with the minimum of clutch slip and without stalling the engine.

For maximum clutch life it is important to develop the skill of pulling away from stationary with the minimum of clutch slip. It would seem that one of the most difficult and potentially damaging situations for the clutch occurs when a car is reversed up a slope into a garage. It is difficult to do this without slipping the clutch. We have also witnessed major clutch damage when driving a car on to a car trailer.

Once a Rolls-Royce clutch starts to slip there is usually little that can be done to cure it apart from renewing the linings.

It is uncommon for oil on the clutch to be a problem. There are sufficient oil catchers and drains to prevent oil from reaching the clutch.

The Bentley 'Light-Type' clutch, and Borg and Beck

For the last two chassis series of the Derby Bentley the 'Light-Type' clutch was introduced, with a lighter flywheel that the earlier model. Apart from the flywheel, the major change was the driven centre plate which now carried the friction linings. Any clutch slip that occurred now took place between the linings and the friction faces on either side of the driven plate. Thus the central steel driven plate was effectively protected; any heat generated went in to the more massive pressure plate and flywheel plate.

However, the Light-Type clutch suffered from the complexity of too many parts. Shortly before this clutch was introduced the Borg and Beck company had developed a clutch working on much the same principles. Being aimed at a much larger market they designed a clutch unit that could be mass produced and manufactured very much more cheaply. Seeing the advantages of the Borg and Beck clutch Rolls-Royce adopted it on all of the late pre-war small horsepower chassis, beginning with the very last 20/25 chassis series and the Bentley 4 1/4L.