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).
From Mr. Gallup to Mr. Robotham discussing brake design regarding proportion, rigidity of parts, and lining.
| Identifier | ExFiles\Box 120\2\ scan0239 | |
| Date | 16th November 1937 | |
| -2- (Mr. Gallup to Mr. Robotham) 11-16-37 open end of any drum and in excess of any intermediate ribs. Such bell mouthing as we have described has been found to be definitely tied up with squeal or chatter. PROPORTION OF BRAKES Because of the lack of an actual vehicle, we are not in a position to comment specifically on your proportion of brakes, front and rear. Our understanding is that the hookup ratio between the front and rear is .82. On the other hand, on the rear you have wider lining, and which we assume, changes the actual proportion of brakes to a somewhat different figure than the .82. In this country, we are tending toward more front brake than on the rear, and this because of the transfer of weight during a brake application and the necessity of preventing a too-early rear wheel slide. It may be that we have entirely misinterpreted the design and this because we do not know whether the hookup is equalized or not. We are assuming that it is, because if it is not, then the numerical ratio you have quoted for the front would mean greater movement of the cam actuating mechanism and therefore, more brakes in front, and which does not coincide with your figure of .82. There is another question in our mind relative to the proportion of brakes, and that is just how the servo mechanism is tied into the hookup. One item, however, we feel is of great importance, and that is what appears to be a "fixed" cam. With this type of cam (if it be fixed) there must be equal wear between the two shoes, but obviously the primary shoe is in a position to do more work than the secondary shoe. We would expect that when the brakes are set up on the production line, unless compensation is made for this condition, the primary shoe would do more work initially than the secondary shoe, because of its geometry and the brakes would have a certain degree of effectiveness and which effectiveness would change as the lining on the primary shoe is worn down to a point where the cam action is limited by the movement of the secondary shoe. We have had in this country, an instance of a mechanical brake so arranged in this manner that it was not only erratic in performance, but was very much inclined to chatter. RIGIDITY OF PARTS The design is typical of Rolls-Royce quality, and on this we want to compliment you. There are, however, certain points which appear to us as inviting comment, and which we hope will not be interpreted as criticisms. The anchor pins and their straddle mounting, the push links from the actuating cam to the shoes, the manner of holding what might be termed the auxiliary or small shoes, seem to us, based on our experience with brakes in this country, as not sufficiently adequate to provide the necessary rigidity and the lack of which is a definite cause of squeal, chatter, and in extreme cases, erratic performance. LINING On the basis of experience which we have had in this country with lining, we are forwarding to you at no charge, 8 pieces of Type 1915 lining Page 2 ..... | ||