18-11-2024, 05:46 PM
Several 30s cars suffered from axle tramp. This is when the front springs hit a natural freqenxy of vibration and start to oscillate violently.
A friend from University had Rover 14s & 16s that used to do this at high speed. I had a 1938 Light Straight-6 Daimler that tended to do this at about 65-70 mph. It was initated by hitting a slight bump and that would set the front end oscillating violently. Each front wheel would bounce up and down in opposition. One would go up when the other went down. The whole car shook violemtly.
The only way to stop it was to decelerate and let it sort itself out. Braking made it worse.
In the case of these cars it was caused by lack of rigidity in the chassis because there could be no bracing round the engine. I think it likely that was one of the reasons that cross-braced chassis came into use.
The Rovers and the Daimlers had harmonic bumpers. These have a horizontal flat spring from side to side with the vertical bumper bar in front. At each end is a cylindrical section with lead weights inside. This spring-mass had a natural frequency designed to vibrate so as to counteract the tramping.
Examples can de seen here:
https://forums.aaca.org/topic/373028-wil...n-bumpers/
It was also essential to have good shock absorbers.
A friend from University had Rover 14s & 16s that used to do this at high speed. I had a 1938 Light Straight-6 Daimler that tended to do this at about 65-70 mph. It was initated by hitting a slight bump and that would set the front end oscillating violently. Each front wheel would bounce up and down in opposition. One would go up when the other went down. The whole car shook violemtly.
The only way to stop it was to decelerate and let it sort itself out. Braking made it worse.
In the case of these cars it was caused by lack of rigidity in the chassis because there could be no bracing round the engine. I think it likely that was one of the reasons that cross-braced chassis came into use.
The Rovers and the Daimlers had harmonic bumpers. These have a horizontal flat spring from side to side with the vertical bumper bar in front. At each end is a cylindrical section with lead weights inside. This spring-mass had a natural frequency designed to vibrate so as to counteract the tramping.
Examples can de seen here:
https://forums.aaca.org/topic/373028-wil...n-bumpers/
It was also essential to have good shock absorbers.
Jim