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).
Modifications to plating and experiments in waterproofing the servo unit.
| Identifier | ExFiles\Box 121\1\ scan0300 | |
| Date | 24th June 1940 guessed | |
| -6- to be 0.005. The plate levers on all chassis are dull nickel plated, and pins chromium plated on 9, 11 and 12 B.V. and 33 G.VII, the rest dull nickeled. These details are shown on drawing Rm.{William Robotham - Chief Engineer}611. On 9, 10 and 11.B.V. the expander housings were reamered to 0.001 oversize on dia. and the wedges and cones were chromium plated to 0.0005 thickness, to avoid rust. These are the only three cars on which the expander unit and shoe link clearances have been altered. In order to keep the lining dust out of the expanders, 3 dozen 26.5 mm. press caps were obtained fitted with cork liners, and are in the Experimental Shop Stores. Since the presence of water in the Servo gives rise to groans or judders causing the brakes to be inoperative, the ideal servo should be completely water-tight. This object was originally aimed at by using Bloomsbury tape, and afterwards plain tape soaked in Neoprene Latex, round the periphery of the pressure and spring plates - also by using special Ferodo washers to bear on the spring plate. These stops were quite satisfactory up to a point, but when once the servo was wet, the water could not get out, and so the ideal of a completely water-tight unit was abandoned. Tests with a "U" tube showed that on cooling the hot servo by pouring water over it, a depression might be obtained up to 3" water, and that the hotter the Servo, the more water entered. The effect was confirmed in the road, but was found to be of academic interest only, since it was discovered that the water got in mainly at the centre of the spring plate, and has considerable effect even when the servo is cold, so that an outlet to the air to remove the depression caused by rapid cooling was found to be of little practical advantage. The weak point was, therefore, protected by means of two circular shields, one fixed round its circumference to the spring plate, and the second inside it and fixed to the gearbox. It was found with this scheme that the servo was impervious to water splashes of the Boylestone variety (3" - 4") although it got wet when actually submerged in the water as at Tissington. Adequate drainage had, therefore, to be ensured. An ordinary servo filled with water with no tape round the circumference, took over five minutes to drain off during which time the brakes were useless; and only after this period could effective 'ironing' be employed to dry off the Continued. | ||