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).
Brake thumping, detailing tests and solutions involving pull-off spring tension.
| Identifier | Morton\M3.4\ img021 | |
| Date | 12th July 1923 | |
| R.R. 493A (40 H) (SL 42 12-7-23). J.H., D.{John DeLooze - Company Secretary} -2- Expl. No. 9940 9941 REF:Hs{Lord Ernest Hives - Chair}5/LMO.9.24. EXPERIMENTAL REPORT. move if the brakes are applied from the off position to the full on position. If the friction is sufficient to prevent the links from moving, then the front brakes come off only the same amount as the rear brakes, - as the front brakes require more movement to return to their off position, it means that there is slack between the driving pegs on the servo drum and the levers so that every time the servo is applied, there is a knock. Our tests however shew that if we increase the tension of the pull off springs on the front brakes and add sufficient friction to the links so that the pull off springs are strong enough to return them to the proper zero position, we can prevent thumping without introducing any other ill effects. On the last car we sent to France fitted with the 12% springs, we made a special test on the brakes fitted to that car to see whether the thumping would come on with running. On that car we eased off the bedding of the wrapping shoe for a distance of 4" from the toe end. The daily reports on that car for the whole of the 10,000 miles show that thumping was non-existant. This rather goes to show that it requires very little modification in order to permanently overcome this complaint. We recommend making the pull off springs on the front brakes to exert at a pressure of 10 to 12 lbs. each when in the off position. We find with the torsion springs contd :- | ||