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 explanation of the causes of front brake thumping when using a servo system.
| Identifier | ExFiles\Box 13\1\ 01-page49 | |
| Date | 16th May 1934 | |
| To Hs{Lord Ernest Hives - Chair} X7360 Hs{Lord Ernest Hives - Chair}/GWH.{George W. Hancock - Head Chateauroux}19/KW.16.5.34. Front Brake Thumps and the cause thereof. The reason why front brakes thump when using a servo system can be classified into several categories. Firstly with the servo assisted system of braking, the front brakes are not directly coupled with the brake pedal and the front application of brakes is left to the action of the servo, friction between surfaces and coupled by mechanical means of levers the pulling on effect of the brake ropes. It will be observed therefore that the smooth action of the front brakes being applied depends upon the efficiency of the servo, and the application of the applied load to the servo friction surfaces. In operating the front brakes there is the load of the pull-off springs of the shoes and brake operating shafts to be overcome before the brake shoes come in contact with the drum surfaces. To obtain this first action of applying the brakes is the cause of thump, and can be caused by the following:- (1) In-efficient servo lining which will not operate until a heavy load is applied to the friction surfaces. The action then is to suddenly grab, with the result that the brakes are applied rapidly and thump. (2) A 100% efficient servo with a light application of load to the friction surfaces may cause too rapid an action in taking up the first motion of the brakes, and produce the same effect. (3) Any weakness in the brake shafts which causes binding has the same effect. (4) Slack brake ropes. (5) Wear of brakes, which causes a lost motion of the servo until maximum load is applied by the foot pedal. (6) Any form of tightness in the brake mechanism causes the load to be applied suddenly. | ||