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).
Overheating of brake drums on the 4¼ litre Bentley and proposing testing aluminium composite alternatives from Hispano-Suiza.
| Identifier | ExFiles\Box 85\1\ scan0013 | |
| Date | 31th January 1936 | |
| W/P - Sr. X206 Hs{Lord Ernest Hives - Chair}/AFM.{Anthony F. Martindale}14/KW.31.1.36. Aluminium Composite Brake Drums. With the advent of the 4¼ litre Bentley the brake system which has not been altered can easily be overloaded when the car is driven by even a moderately fast driver. We enclose two graphs, one of which shows how the co-efficient of friction varies with temperature in the case of various friction linings tested by the I.A.E. On this graph you will see that 220°C. is the critical temperature which brake drums should not exceed. The other graph shows what temperature a standard rear drum can reach on a 4¼ litre Bentley. You will appreciate that in order to reach this temperature the driver has to pass through a dangerous period, which fortunately does not coincide on both front and rear brakes, and that when this temperature is reached, the brakes become incredibly fierce and may give rise to front brake judders at high speed. (This has happened to one of our cars and the axle was scrapped). Also, the wear at high temperatures of the brake linings is enormous and the Ferodo is permanently damaged. On the second graph you will also see the temperature attained on the same car on the same run by an aluminium-steel drum, and no doubt you will agree that this drum has very desirable characteristics. The only objection to it that we know of at present is its cost, as the Nickel Manganese Chromium Steel liner castings cost 18/- a piece on a production basis. The reason for the use of this metal is that it has an expansion of 21 x 10-6 per °C., and it was inserted with an interference fit. Hispano-Suiza have been using aluminium drums for years. As far as we know, the aluminium is cast round the liner and they use an ordinary steel or iron for the latter. We do not see how they get away with this as we have scrapped such drums; but this construction is much cheaper. Hs.{Lord Ernest Hives - Chair} wants us to try a Hispano drum, and the object of all this preamble is to ask you, can you obtain for us a Hispano rear drum and hub and brake actuating mechanism complete, so that we can test it exhaustively? We should be very much obliged if you could. | ||