From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Investigating complaints of slipping clutches on the 25 HP model.
| Identifier | ExFiles\Box 103\1\ scan0012 | |
| Date | 31th January 1933 | |
| To Wor.{Arthur Wormald - General Works Manager} From Hs.{Lord Ernest Hives - Chair} c. to C. c. to PN.{Mr Northey} c. to Br.{T. E. Bellringer - Repair Manager} c. to Hd.{Mr Hayward/Mr Huddy} 25 HP. CLUTCH COMPLAINTS. We have been waiting for a chance to investigate the 25 HP. clutch slipping. Cricklewood telephoned us up that there was a car coming in with this complaint, so we sent a man down to investigate it. The car was driven for about 130 miles by Cricklewood test drivers and they could not reproduce any sign of slipping. The clutch was taken down and examined and there was no apparent fault with it to cause it to slip. We believe Cricklewood criticised the bedding, but this would not be sufficient to make the clutch slip. Whilst our man was there they also investigated another car, Mr. Bradley's. This car was tried out on Brooklands and on the test hill but the clutch slip could not be reproduced. We are certain there is no mystery about the clutch slip on the 25 HP. cars. From our investigations we think one of the chief causes of these clutches slipping in the mysterious way that is reported, is due to the binding of the pressure plate in the serrations. If the clutch is slipped excessively the pressure plate expands and binds in the serrations; this causes it to bind up worse than ever. As soon as the clutch cools down the clearances become normal and the clutch will then not slip. We think Cricklewood should dismiss from their minds that there is anything mysterious. The 25 HP. clutch is very simple and normal in design. The spring pressure and coefficient of friction on the material which we allow is sufficient to cover any variations which are likely to occur. This does not include oil. If any oil gets on to the clutch we expect it to slip. In order to clear the trouble on the serrations all future cars we are altering the shape of these from involute to parallel. This is similar to what we are using on Phantom and Peregrine. It is simple by tests to show whether the serrations are binding without dismantling the clutch. If two or three starts are made with the car from a standing start on third gear with the engine running fairly fast and careful note is made of the freeness of the clutch pedal it will be found that if the serrations are binding and as the clutch becomes hotter, the pedal movement becomes sticky. | ||