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).
Analysis of brake judder, focusing on friction linings, temperature effects, and tests on various chassis.
| Identifier | ExFiles\Box 85\1\ scan0146 | |
| Date | 20th July 1936 | |
| -6- (5) To a standard car, aluminium drums which are exceedingly rigid were fitted. This car juddered very easily, and adding swinging arm damping, reducing the arc of contact, etc., made very little difference. (6) It was found on 20/25 HP. chassis, Bentley and Vulture that reducing the pull-off spring poundage in the front axle torsion shafts greatly reduced the tendency of these cars to thump and therefore judder. (7) A characteristic of friction linings is that if they are repeatedly heated to 300°C. the coefficient of friction, µ, becomes unreliable; instead of remaining at 0.38 when cold, and falling perhaps 40% when warm, µ varies in an indeterminate manner between 0.20 and 0.65, or it may even vary through a greater range. These figures were determined on a rig. If such a high coefficient as .65 should be experienced on the road, judders would occur very easily, and when they did occur would be exceedingly violent. (8) During certain brake drum temperature tests on a completely standard 4¼ litre Bentley it was found that the drums repeatedly reached the temperature of 300°C., and sometimes exceeded it. On some of these runs, very violent judders occurred, doing considerable damage, on gentle brake applications and not necessarily when the brakes were first applied. The same thing has recently been experienced on B-36-BN{W.O. Bentley / Mr Barrington} in France. Also, an examination of the Ferodo on 4-B-IV subsequently to its accident showed that the linings had been heated to 350° - 400°C. With aluminium drums it is practically impossible to exceed the temperature of 200°C. | ||