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 the high pedal effort and inefficiency of the Spectre braking system.
| Identifier | ExFiles\Box 92\4\ scan0020 | |
| Date | 29th October 1934 | |
| To E.{Mr Elliott - Chief Engineer} c. to Wor.{Arthur Wormald - General Works Manager} c. to Da.{Bernard Day - Chassis Design} c. to By.{R.W. Bailey - Chief Engineer} c. to Hdy.{William Hardy} Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls}1/KW.29.10.34. SpectreCodename for Phantom III Brakes. Owing to the enormous pedal effort required on this car to take up the brake clearance and to stop the car while shunting, we have measured the efficiency of the linkage from the pedal to the front brake cams. Curves are attached of the efficiency including and excluding the front equaliser. As a comparison, Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer}4/LG.19.4.29 gives a figure of 60% for the efficiency to one cam of the direct to rear braking on a 40/50 chassis for a pedal load of 100 lbs. In spite therefore of the Girling system we have not improved the direct braking efficiency, due presumably to the increased number of moving parts. In the inefficiency shown for the SpectreCodename for Phantom III is included the pedal return spring of 5 lbs. and the servo separating spring. Since the rear brakes were left working, inefficiency of the swinging arm is included for such loads as caused it to move. A pedal effort of 35 lbs. is required on the Phantom to take up the brake clearance. It does not seem likely that we shall be able to reduce the 100 lbs. required by the SpectreCodename for Phantom III now. To stop the SpectreCodename for Phantom III while shunting on a gradient is almost impossible. On the Bentley we have had considerable difficulty in making direct braking to all wheels function nicely. We have had to stiffen almost every part of the brake linkage, reduce the direct braking below what could be used on a heavier car, and remove all exterior pull off springs which we can do because of a higher mechanical efficiency. Our reason for persevering to this extent is that the Bentley, being a sports car, requires the ratio of front braking to be as high as possible, which ratio must not vary. | ||