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).
Letter from Ferodo Limited discussing brake lining noise, glazing, and performance comparisons.
| Identifier | ExFiles\Box 26\4\ Scan280 | |
| Date | 19th February 1926 | |
| From FERODO LIMITED. 19/2/26. Sheet No. - 2 - Messrs Rolls Royce, Limited. ordinary testing work we frequently get loud whistling when running a piece of lining against a solid steel drum weighing between 5 and 6 cwts, but it is readily seen that the drum itself does not vibrate and that noise is caused by vibrations of the mechanism carrying the samples, so that it is quite possible for the brake shoes and operating mechanism of an ordinary car brake with very solid drums to produce whistling apart from any vibration of the drum itself. In certain conditions any factor that increases or decreases the actual frictional tension between the rubbing surfaces, will produce noise or prevent it - for example, practically any brake will scream if a little grey paint is allowed to dry on the metal surface; resin powder has a similar effect. On the other hand, a few spots of oil, paraffin, water, graphite, etc., will generally produce instant silence, but generally, shortening the length of the lining of the brake is effective. Clamping a fairly solid metal ring round the outside of the drum will cure the worst Morris squeaks we have every heard. Again, Ferobestos Lining is very effective. In the cutting you enclose, it is recommended to scrape the lining to remove the "glaze". We know, of course, that certain makes of lining do actually glaze, and in this condition the friction is of extremely low value and braking consequently is ineffective, but never within our experience has an ineffective brake produced noise, in short, we say that when noise obtains the lining is too efficient from the point of view of its friction value. In general, so little margin exists in brake pressure application that it is rather dangerous to recommend any reduction in the friction of the lining, since the Servo action of all shoes will magnify greatly, any slight differences one way or the other in the friction, and for pure inconsistency to blame the loss of braking power to glazing of lining and then suggest that glazing is the cause of brake shriek appears to us to be very nearly the limit. You refer to the mileage run by Ferobestos on your Test Cars. In this regard, we really can offer no explanation of the wide difference between its performance and that of Ferodo Bonded Asbestos. Under our test conditions, the latter certainly has the advantage but there is really very little between them. The life of Ferobestos can be largely increased if we reduced its friction value, and in view of your remarks as to the pressure available from your Servo motor we are submitting samples of oil-treated fabric - not just fabric doused with oil, but with the lubricant incorporated in the bonding ingredients during the course of manufacture. We supply large quantities of this material to Railway Companies for very heavy duty where resistance to wear is the prime object. We are absolutely satisfied that this class of material will eliminate brake squeak, except that which may momentarily obtain if the surface of the brake drum becomes slightly oxidised. Yours faithfully, F E R O D O L I M I T E D Chief Engineer. | ||