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 discussing knocking issues and testing methods for controllable hydraulic dampers on a 20/25 HP chassis.
| Identifier | ExFiles\Box 27a\1\ Scan416 | |
| Date | 30th April 1936 | |
| To Rolls-Royce Ltd. Derby......... Hs{Lord Ernest Hives - Chair}/LES.{Ivan A. Leslie} Levallois Sr/VA2/ET.30.4.36 Re: TESTING CONTROLLABLE TYPE HYDRAULIC DAMPER POUNDAGE. With reference to the conversation we had with you during your last visit to Paris concerning knocks from the above type of damper, especially the rear ones, we have, as you are aware, had quite a number of complaints and we have not, up to the present, been able to determine the exact cause. We attended to a complaint a few days ago on a 20/25 HP. chassis (GHG.I). The car had only covered a total mileage of 7000 Kms. There was a distinct knock from the rear dampers, but more pronounced on one than on the other. We dismantled the dampers and, apart from a very slight amount of slackness, if it could be called slackness (we would rather have called it a standard working clearance), in the bronze bushes of the main lever, nothing was found to be wrong. We made and fitted two new bronze bushes and finished them by hand scraping, and when the lever was fitted in position it was a little on the stiff side. We checked the poundage and it was found to be O.K. The dampers were fitted to the car and the knock had disappeared. As there was such a small amount of slack in the original bushes (in fact it could only just be felt with the bushes and the cylindrical part of the lever in a dry condition), the matter has rather puzzled us. We shall be interested to learn from you the method you adopt in the Experimental Department when checking the poundage of dampers. We do it with the aid of a circular spring balance and extension levers which the Works sent us specially for the job. We find that one has to be very careful re the speed of the "pull" on the lever, otherwise the readings vary. Do you time the speed of the "pull" when you check dampers? We mention the above because we are going very carefully into the question of knocks etc.. Have you tried taking out side play between the intermediate lever and the bronze bushes and compensating for this by reducing the width of the "flats" at the lower end of the intermediate lever or that part which fits into the slot of the piston? We are aware that a certain amount of end play is necessary for centering or alignment purposes. If you have any dope to offer, we shall be very glad to receive it. It is understood that the next time we come across two rear Bentley dampers that are knocking badly, we are going to send them to you for examination. By the way, we have received a set of new front and rear dampers from Works for replacement purposes. We have also received several sets of bronze bushes. Sr/VA.VA | ||