Letter detailing adjustments made to the brake servo system to correct an issue of excessive front braking.
| Identifier | ExFiles\Box 11\2\ 02-page193 | |
| Date | 17th April 1929 | |
| To Hs. {Lord Ernest Hives - Chair} and Rm. {William Robotham - Chief Engineer} From G.W.H. Hotel de France Chateauroux(French test region) Indre 17/4/29 (Vertically on left) F.R.BRAKES (Top right corner, handwritten) 41 We have received your letter of the 15th and in reference to it, we belive our report has not been clear. We are getting ample braking on the rear brakes, in fact more than is necessary but the front has been more than this preportion, therefore as stated there is too much front braking. This was not determined by the squeaks, but the front braking had got to such a state that it became dangerous, we agree that too high a serve efficency aggravtes it and when the brake shoes get into a very dry state the efficency of the brakes goes up by leaps and bounds, the braking being approximatly 50% more than with the shoes in a normal state. We find this happens chose what brake linings have been used, please note we are not speaking of squeaks, which is another matter to deal with. The front brake shoes to get into this condition have had too much work to do in the first instance, therefore we say that the front braking requires irrespective of serve efficency decreasing. We definitly state that the sales dept will very quickly be up against this in a short time if the leverages are not altered. We could not alter the levers on the front brake countershaft as forgings would be required, so therefore we reduced the efficency of the serve by increasing the lengh of the "T" arm thus decreasing the front braking. We belive we are right in stating that the preportion of increase to the rear brakes is only got by increasing the foot pressure applied to the foot pedal. We did not work haphazard in arriving at the solution. We first obtained the load required to pull on the "T" lever to operate the front brakes and by increasing the lengh of the bottom arm, the load required to operate the front brakes was increased by 25%. This means in operation the servo would be less efficent but still efficent enough for the rear braking, plus the foot pressure. We should obtain the same results if the return lead of the front brakes were increased considerably. The lubricated serve efficency is about right for the braking efficency of the car generally and by altering the leverage by way of the countershaft to the front brakes would give ideal results. We agree that the preportioning of the leverages is right on paper and right as taken either side of the serve for the Phantom but what has to be rekoned with on the S.S. is the loss in the rear brakes due to sponginess of the drums and winding up of rear springs. The pull of the serve to do this is not lost on the front brakes in the same preportion, hence more braking takes place in the front than what your figures give, also the fitting of the central arm has given us more efficent front brakes. We have sent you the results of our tests, we can now pull up with saftey, the rear brakes are doing ample work and the steering is not affected by the front braking. Our rear brakes have been squeaking for some days, the front with light braking. We should be very much obliged if you would send us levers giving 20% reduction on the front brakes for trial. G.W.H. (Handwritten, bottom left) Royss | ||
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).