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 issues with brake fading on the Bentley 2-B-IV model and proposed solutions.
| Identifier | ExFiles\Box 84\2\ scan0290 | |
| Date | 1st February 1935 | |
| Bentley Brakes. We have had complaints from Bn.{W.O. Bentley / Mr Barrington} on his car 2-B-IV and on a few customers' cars of sudden fading of the brakes after use on a twisty road. We recently had an opportunity of driving 2-B-IV from Derby to London via the Red Gate. About 30 miles out of Derby there was without any warning no braking available for an approaching corner. When the brakes were allowed to cool they again became efficient but after a few more stops once more disappeared. We were of the opinion that the cause of this trouble was due to the servo being on its stop. With the brakes hot the front could be taken up 3 half turns. When the car next arrived in Derby the brakes, cold, could be taken up 3 half turns in front and 4 at the back. Under this condition, running in 1st gear with the wheels jacked up, the servo reaches its stop without stalling the engine and the pedal was still some way from the floorboards. We know that this state of affairs does exist. Due to sponge in the front brakes, the servo reaches its stop before the driver, by the position of the pedal, is aware that the brakes need adjusting. On 2-B-IV the situation was aggravated by (1) slack in the front brake ropes, (2) lost movement in the servo travel of about 3/8" due to incorrect setting and (3) the amount of front braking being higher than is standard, the servo linings and cam angles being conducive to this. We are fitting to 2-B-IV brake levers that give 37% less multiplication from the servo to both the front and rear brakes, the amount of braking being brought up again by alteration to the servo cam angle. Exactly this scheme was fitted to Hall's car for the T.T. race. We should like to add that on several occasions we have asked the Design Dept. for a servo in which the output torque is provided by a chain wrapping on a drum. In its simplest form this would increase the servo travel from 90° to 270°, and would make absolutely sure that the state of affairs existing on 2-B-IV could not happen. Until we are in a position to get such a servo we recommend in cases of complaint decreasing the leverage, in the manner stated above. Contd. | ||