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).
The rationalised braking system for the 12.B.V. model, detailing its faults and modifications.
| Identifier | ExFiles\Box 121\1\ scan0292 | |
| Date | 11th June 1940 guessed | |
| Brake file. 1029 RATIONALISED BRAKING AS FITTED TO 12.B.V. This system consists of hydraulic front brakes which are required for Independent Front Suspension, and mechanical rears, it being preferred to avoid complete reliance on the hydraulic system. The system is assited by a friction disc servo motor on the gearbox, designed to reduce pedal pressures without increasing the pedal travel. The hydraulic part of the system is all Lockheed except for the wheel cylinders which are of special Rolls Royce design, but similar to the Girling expander units except that the wedge is pushed instead of pulled against the cones. Girling shoes and adjusters are used, but an extra pull-off spring is required to eliminate front brake "drag" due to residual line pressure. Rolls Royce balancing links are fitted between the shoes as used on the rear brakes. A simplified handbrake with Bowden release has been put on some of the chassis, similar to PL.68 for the L.H. Senior Range. There are two serious faults in the system, namely: 1) Rear wear is 3 or 4 times as fast as front. 2) Servo judders, rendering brakes quite useless. 1. Uneven Lining Wear. (particularly on 8 cylinder cars). There has not been time to go into this question in detail, but the following steps have so far been taken. a) Since some of the cars definitely suffer from lck of front braking, the shoe balancing links were removed on the front brakes of all 8 cylinder cars. This is a makeshift method, since it allows the leading shoes to wrap and wear considerably faster than the trailing. The standard brake lining arrangement at present is Ferodo BZ on the leading shoes, being a good wearer low, and no squeak but a tendency to fade at high temperatures; and Ferodo R.U. on the trailing shoes, having a high with a tendency to judder at high temperatures if used on the leading shoe. The combination eliminates squeak and gives even wearing when the balancing links are used. Some of the cars have had their overall pedal ratios and, incidentally, their Front/Rear ratios, increased by reducing the servo cam angle from 35 deg. to 30 deg. giving an increase in Servo coefficient from 1.87 to 2.26. The theoretical ratios for the two systems are as follows: 35 deg. Cams. Direct Rears 30.4) 58.4) Ratio F/R = 1.24 Servo 28.0) Servo Fronts 72.5 ) Continued. | ||