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 frame sag, vibration, and booming issues in a long wheelbase vehicle.
| Identifier | ExFiles\Box 43\2\ Scan115 | |
| Date | 20th April 1926 | |
| Oy1-E-42026 -2- April 20, 1926. Thinking this might be an effect of frame sag due to the long wheelbase, we - (1) Disconnected the rear body bolts and removed the body shims, leaving the rear part of the body overhanging. (2) Fastened a string round one end of the rear axle and brought it up through the open seat well. 1. By holding a finger at the gap between frame and body sill we could get an idea of the motion of the kick-up portion of the frame relative to the body sill. There is plenty of relative movement but it is much faster than the frequency in question, at least 600 per minute. It is sufficient however to account for a lot of booming and shows the absolute necessity of shimming the body on at least 3/8" rubber at the rear end, if nowhere else. The inference is that every new car or overhaul job should be mounted on rubber at the kick-up, to avoid booming and rattles in the body, drumming of window glass, rattle of wiring cables, etc. The vibration is so continuous at the rear end that it is remarkable that we get no cases of loosened nuts or broken fuel piping. 2. The string from the axle gave us an indication of the relative movement of the axle and body. Since the relative position of the axle and body defines the compression of the rear springs it is also a measure of the forces transmitted from the rear springs to the body. The result of this test was that the movement of the axle on all ordinary roads such as we have been testing on is very slight and gradual, in fact we stood on the rear axle through the open seat well and rode comfortably up to 30 m.p.h. Occasionally the rear axle will get into a state of vibration but this is rapidly damped out, and occurs at a high frequency, probably 500 a minute. It certainly does not account for the "joggle" in the car. | ||