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).
Clutch reliability tests, comparing wear and performance of different facing materials.
| Identifier | ExFiles\Box 129\4\ scan0101 | |
| Date | 13th December 1937 | |
| -2- in a short time rather than to test the general reliability of the clutch. Arms were arranged from the operating levers so that the pressure plate movement was increased by 20 to 1 so that facing wear could be measured at intervals during the tests, and the figures so obtained agreed almost exactly with the measured wear observed on dismantling after the tests. The unit was first fitted with standard Ferodo R.A.D.11 facings and standard springs of 141 lbs. mean, this giving a working µ of .18. During the first 60 slips there were periods of excessive slipping when the clutch almost failed to pull down the engine revs. slipping at times, continuing for 5 seconds with resultant excessive heating but after this period no further excessive slipping occured with the exception of a brief period at 300 slips and another at about 640 slips. The test was concluded at 1,000 slips when the facings had worn down to the rivet heads. The wear of each facing was.055 but the wear of the driven plate was negligible, although it was badly dished. We have occasionally seen the driven plates of customers cars worn, although some are not, and suggest that the difference may be due to road dust acting as an abrasive. The heating had resulted in the mean spring poundage falling from 141 to 132 lbs. or a total drop of 72 lbs. which brings the working µ to .192. The rate of wear of each facing is shown on curves Rm.{William Robotham - Chief Engineer}476 attached. The clutch was then faced with Graphite Bronze, the same springs being used. For the first 20 slips the pick-up was almost equal to that of the R.A.D.11 and slipping not excessive, but it quickly increased and at 40 slips the test was abandoned owing to the springs having dropped to 125 lbs. or 11½% down. | ||