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).
The specifications and requirements for a hydraulic jack system for a motor car.
| Identifier | ExFiles\Box 26\3\ Scan058 | |
| Date | 28th February 1930 guessed | |
| -2- extreme occasions one could slack back the jack hydraulically after the first attempt at lifting and screw out the extension. This gives a hydraulic lift of 5.750 ins. If the camber of the road be convex there might be some doubt as to whether the jack would go under the axle, but as the distance between the wheel and the spring is only 15 ins. it is a very severe camber that would make much effect in the clearance under the axle. A concave camber is dealt with by extending the screwed extension. We now have the following proposed conditions. MINIMUM HEIGHT = 6.000ins. or a little less if possible. Hydraulic lift = 5.750ins. plus .500 for extra deflection of rear tyres. = 6.250ins. Extension = At least 3.000ins but more if possible. These figures agree with those you have given except in - (1) We only allow 1.000ins. for soft earth. (2) We do not cater for a lost cover. There will be no difficulty in getting a jack to these requirements, and we are seeing the Skyhi people this week. We would be glad if you would give us your remarks after considering carefully our suggestions. We would point out that whilst you will not agree to a hydraulic jack with a minimum height of less than 5.500ins you have passed the Dunlop, we presume, and that is, according to your stating, 6.300ins. With respect to your remarks re DaVEy being stuck on the road one dark wet night with a jack that will not lift the car, he has experienced this, though not because of the lift of the jack, but owing to the difficulty of placing the jack in position under the rear axle, on a car with a trunkard and two wheels at the rear. It is very difficult to operate the Dunlop Jack in this position, and it is because of this that we are being asked for hydraulic jacks, and also the Jack-ALL system. We will keep you informed of any progress we are able to make and would welcome your help. EV.{Ivan Evernden - coachwork} We are looking into the Jall-ALL system as fitted to H.R.H. Prince of Wales' Car. | ||