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 Borg & Beck Co. Ltd. discussing clutch spring modifications due to excessive pedal pressure.
| Identifier | ExFiles\Box 85\2\ scan0359 | |
| Date | 29th June 1938 | |
| Borg & Beck Co.Ltd. -2- 29.6.38. with the result that the total thrust is considerably higher than that anticipated, the actual poundage being still further increased by the fact that the Black spring has a rate of, approximately, 220 lbs per inch against 166 for the Brown. On a clutch we have carefully examined, we found the mean poundage of the nine springs was 159 lbs @ 1.687, but as the working length was .125 under 1.687, the actual poundage was 159 + (220 x .125) = 186.5, giving a total thrust of 1678 lbs. This thrust was closely confirmed by a test made on our testing rig, which measures the total thrust assuming a pressure plate thickness of .330". The nett result of this is excessive pedal pressure and it will, therefore, be necessary to modify all the clutches supplied with Black springs. Our suggestion is to remove three of the Black springs, and replace them by three Green. We thank you for your offer, per 'phone, to carry out this change on a few clutches in the course of a day, and we are arranging to send you 93 by road, probably to-morrow, and would ask you to return, say, 12 of these, as quickly as possible. From the above, it is clear that the reason for changing from the original Brown spring was because so many of those supplied were under the required poundage, and the new Black spring is considerably above the required poundage owing to the combination of its higher rate and reduced length. We are bearing the cost of dismantling a number of clutches from completed chassis, and delivering the clutches to you. We trust, therefore, that you will see your way to change the springs without charge to us. Yours faithfully, For ROLLS-ROYCE LTD. | ||