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 performance focusing on F/R ratio, hydraulic pressures, servo operation, and the sequence of brake application.
| Identifier | ExFiles\Box 121\1\ scan0293 | |
| Date | 11th June 1940 guessed | |
| -2- 30 deg. Cams. Direct Rears 30.4) 64.4) Ratio F/R = 1.35 Servo Rears 34.0) Servo Fronts 88.0 ) Two of the 8 cylinder cars (11.B.V. and 4.B.50) have also had their F/R ratio increased by nearly 20% by means of a special lever Ex.36768 on the cross-shaft. These cars have not covered sufficient mileage to prove themselves. b) A device was made to measure the pressure at the expander cones with shoes removed, the effort being reduced 3-fold and measured by pressometer fitted with a 250 lb/sq.in. gauge; a rough test on the "Ripple" showed that the hydraulic fronts were probably less efficient than the rears, thus making the actual F/R ratio correspondingly less than the theoretical value. However, it is known that the rear equaliser gives more pull on the offside than on the rear, which might neutralise the effect, since our tests were on the off-side. On the run down from maximum pedal pressures of 100 and 110 lbs for the two curves, the latter are roughly divided at 20 lbs. pedal pressure into two sections with different gradients, and from the shapes of these curves it is seen that if the pedal pressure were never taken above 40 lbs. the rears would undoubtedly do most of the work on releasing the pressure. It seems clear the the F/R ratio of this car should be increased from 1.24, but further conclusions can hardly be drawn from these curves which may be inaccurate due to fading of the Servo lining which became somewhat heated. It has also been noticed with floor boards removed, that the rears come on first, and only when all the rear clearance has been taken up does the master cylinder plunger move forward. It is known that the skin friction is considerable, and that extra strong pull-off springs have to be fitted to stop front brake "drag", and so on applying the brakes both the skin friction and the spring have to be overcome. It is suggested that the order of operations on gradual application of the brakes is as follows:- The master cylinder plunger first moves forward just enough to cover the hole connecting the cylinder with the reservoir and the rear shoe clearance is taken up. Then while the skin friction and the extra heavy front return springs are being overcome enough to take up the front shoe clearance, the rears are always ahead to that extent, the effect being most noticeable at low pedal pressures. As the pedal pressure rises, the front braking force catches up and passes the rear, which helps slightly to compensate for the increasing transferred weight. Continued. | ||