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).
Investigating the cause of poor braking performance and 'sponge' on the Spectre car brakes.
| Identifier | ExFiles\Box 92\4\ scan0053 | |
| Date | 21th January 1935 | |
| To E.{Mr Elliott - Chief Engineer} c. to WDP. [text crossed out] c. to Da.{Bernard Day - Chassis Design} ________________ Hs{Lord Ernest Hives - Chair}/APM.17/KW.21.1.35. SpectreCodename for Phantom III Brakes. In previous memos, we have mentioned that we have been unable to obtain good braking on the SpectreCodename for Phantom III car. We have also measured what braking torque the front brakes will give, and we have found it is very low. Now we have made some "sponge" measurements which throw some light on this trouble. We fixed micrometer clocks to the brake actuating lever inside the drum, and to the brake shoes. Thus we obtained the relative movement between these two components. We find that the theoretical relative movement is the actual movement when the brake drum is removed and there is no load on the mechanism. When the brake drum is in position, however, under maximum load the movement is only one third of what it should be. This lost movement can only be due to - (1) Compression in the toggles. (2) Bending of the actuating lever. (3) Bending of the shoe. (4) Wind up of the adjusting mechanism. Of these, (1) and (2) are thought to be negligible. (3) is estimated at 2 or 3 thousandths, see memo. Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls}35/KW.21.9.34. The clock was 2 1/4" from the toggle pivot. This leaves (4) and we have known for some time that the wind up in this mechanism is considerable. The attached graph gives the results obtained, the very small opening of the shoes accounting for the poor braking on the road. We are unable to detect any end movement, due to sliding of the splines, of the adjustment mechanism. Hs{Lord Ernest Hives - Chair}/A.F.Martindale. | ||