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).
Letter from the Experimental Dept. to Monsieur Henri Perrot regarding various Ferodo brake linings used on Bentley brakes.
| Identifier | ExFiles\Box 141\2\ scan0294 | |
| Date | 9th June 1939 | |
| 1180. Experimental Dept. Rm{William Robotham - Chief Engineer}/AFM.{Anthony F. Martindale}7/MH.{M. Huckerby} 9th. June, 1939. Monsieur Henri Perrot, 32, Rue Madame de Sanzillon, Clichy (Seine), Paris, FRANCE. Dear Sir, Mr. W.O.Kennington has told us that you would be interested to know what linings we use on Bentley brakes. Originally we fitted Ferodo MR. This lining has a high co-efficient of friction (μ) when cold, the value being 0.38, but this can be reduced to one third this value when really hot. The chief objections to MR are, that it becomes extremely inconsistent when once it has been hot, μ can vary between 0.1 and 0.5, and that it is liable to squeak because it contains a synthetic resin. On a car with less performance than a Bentley, or more generous brakes, these defects might not be apparent. We then changed to Ferodo BZ. This has a slightly lower co-efficient of friction than MR, μ is about 0.35. The lining is more consistent, the lowest μ we have ever measured is .16. Although it also is a synthetic resin bonded lining it is less liable to squeak than MR. We are next going to fit a mixture of Ferodo BZ and Ferodo RU in the same drum. RU is a rubber bonded lining. The sole reason for this change is that this combination is much less liable to squeak. The smell of rubber is not notice-able except when the lining is new or extremely hot (500°-600° Centigrade). | ||