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).
Technical memorandum discussing the testing, durability, and improvements for overdrive boxes, gears, and servo systems.
| Identifier | ExFiles\Box 99\4\ scan0285 | |
| Date | 10th March 1939 | |
| - 2 - Da{Bernard Day - Chassis Design}/Hdy.{William Hardy}3/G.10.3.39. We have an improvement in reserve for No.4 for overdrive boxes, as the diameter of the washer can be increased with overdrive ratios. We do not anticipate trouble with 3, 4 or 5. Features which have had considerable testing, but which it may be thought, cannot yet be regarded as conclusively proved are :- (a). Strength of over-drive gears. (b). Strength of coupling teeth. (c). Durability of overdrive and direct synchronising cones. As regards the overdrive gears, the Lewis stress (62,000) is practically the same as for the 'M' series Bentley (59,500) but only by reason of a diametral pitch of 10 instead of 14 for 'M' series. It may be thought that when the gears have completed 50,000 miles hard driving on overdrive in France, they will have had a test which it is unlikely any customer will reproduce. The same test should do for the coupling teeth, but we suggest that they are given harsh treatment on over-run to test for fatigue of the four teeth which take over-run torque. The small overdrive and direct cones have not been functioning in the test in France, and so we cannot conclude anything from this. However, appearances in other cars do not as yet indicate that the durability will be insufficient. Servo. I am informed that there are no serious troubles on this. I am not certain we yet know that the brake linkage on the gearbox is sufficiently durable. I believe that the box in France has the old type linkage. Nor have I heard that overload testing of the servo and brake gear has been carried out to reveal weak features. This cannot be done on the road, as the rear wheels lock and stop the servo. Da{Bernard Day - Chassis Design}/Hdy.{William Hardy} | ||