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).
Technical report on rear suspension, detailing issues with interleaving materials, spring specifications, and the use of rebound straps.
| Identifier | ExFiles\Box 152\2\ scan0214 | |
| Date | 1st May 1940 guessed | |
| -7- Rear Suspension. Interleaving is the chief snag on rear suspension. Ferodo's Jackson board with bakelised tips will last for 15,000 miles probably. Spauldite will only last 8,000, but rubber pads at the ends are said to double its life. There are some in my drawer, which should be put on Ripplet and 31-G-VII. Mobilgrease in the grooves has been tried with Spauldite but it did not seem to do any good on 11-B-V as the longest interleaf was worn through at one end after only 5,000 miles. American board and Woodhead interleaving are no good. Ferodos have got a rig running to test the coefficient of friction and life of interleaving. They run the interleaving with a pressure of 500 lbs. spread over 2sq.ins. of it, with a movement of 1/8" at a speed of 133 cycles per minute. They ran Woodhead interleaving with the following results. The coefficient of friction started at .35, dropped to .19 after one hour until ten hours, and then rose steadily to .38 after 50 hours. The total wear was .005". Obviously the lowest possible coefficient of friction is required. Ferodos are carrying out further 50 hour tests on Spauldite, bakelised board and American board. As regards cost Spauldite is cheaper than tipped Jackson board, about 2/6d against 4/- per spring. The spring deflection generally used has been 7" though some 5.5" springs were tried on Corniche but were not found to be necessary. 950 lbs. springs are in stock for Ripplet, and pairs of 850 lbs. and of 900 lbs. should be ordered for Rippletto. A new rear spring drawing is required showing the rate of the spring instead of its free camber because the rate of a spring in general starts low so that the free camber should be greater than the deflection required. Woodheads should be asked to mark the actual poundage on each spring with a tolerance of about 10 lbs. either side of the nominal poundage. They should also be asked to tap the 2.B.A. holes which take the screws which locate the bushes in the spring eyes and stop them turning. And they should be shown the main leaves on the springs in the rack off 11-B-V; on them the main leaf starts to bend into the central rolled eye several inches from the end of the second leaf. So all the load comes right on to the end of the second leaf over a minute area and no interleaving could hope to stand up for long. The reason for using springs with interleaving is to do away with the need for grinding the spring leaves and lubricating them. This reduces the cost by nearly 30/- per spring. Rebound straps to limit rebound to 3.5" have been fitted to 10-B-V.{VIENNA} They include soft progressive buffers and seem quite satisfactory. They require endurance testing and official approval. The only reason for rebound straps is to make jacking up easier. Rebound straps require ordering for Ripplet, and should be put on at the same time as Gordon Armstrong shock dampers in front of the axle. There is a scheme, PL.145. | ||