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).
Testing lighter clutch thrust springs to resolve issues of grab, judder, and slipping.
| Identifier | ExFiles\Box 93\3\ scan0416 | |
| Date | 23th March 1938 | |
| -2- Rm{William Robotham - Chief Engineer}/NRC.{N. R. Chandler}2/MH.{M. Huckerby}23.3.38. We therefore decided to try a set of lighter thrust springs, and tested the existing springs which were only 2½% under standard poundage, and the new springs fitted were 16.5% under standard (or 14% lighter than those removed). By.. MX.{John H Maddocks - Chief Proving Officer}, GWR. and NRC.{N. R. Chandler} again took the car over the same course, and failed to produce any grab or judder, the engagement being particularly smooth, also an appreciable reduction in pedal pressure was observed (this car has the short pedal travel standard prior to D series). Finally, tests of severe slipping were made on a steep hill, in order to prove that we had not overdone the reduction in thrust pressure, with resultant risk of slip, and we were satisfied that the clutch would take up the drive even when engaged with engine racing on too high a gear for a quick get-away. This test, which we consider abnormally severe and outside the range of normal driving, was repeated three times, so that the clutch became excessively hot, which materially increased the tendency to slip, but after only a few minutes cooling the µ was completely recovered, and the take up again became normal. Subsequent starting tests showed the take-up remained good, but under some conditions we thought it was possibly not quite as good as before the "roasting", we therefore decided to fit new facings so as to be on the safe side, as the customer will tend to be super-critical, although we are of the opinion that the complaint would be cured even with the original facings. With the original springs the working µ was .196, and with the new springs .228, which is about the same as the 4¼ litre Bentley with Brown springs, and while we are satisfied that these new springs will not permit excessive slipping, we do not recommend a further reduction. Our previous experience, prior to the recent isolated cases of customers' complaints, had not indicated any particular need for weaker springs, but we are looking into the matter of providing a stock of lighter springs, which we propose to paint a distinctive colour, for any future complaints, as these could be fitted at a very small cost once the clutch has been dismantled. | ||