When you view the Falcon from the side you will note that the eyes of the rear spring are at different heights above the ground. The front eye is lower.
#1. Here's where the geometry comes in:
The rear axle of the Falcon DOES NOT move up and down in a true vertical direction (90 degrees to the gound) by design.
As the axle moves upward in relationship to the body it (the axle) also moves slightly forward. That shortens the distance between the center of the wheels on one side of the car (in this example only one rear wheel is moving upward). This causes the rear axle to steer the rear of the car in the opposite direction the turned front wheels are taking the front end of the car. The result is oversteer.
Or as the classic remark states, "A car trying to follow a curve will go off the road front end first". Ford U.S. designed the oversteer into the Falcon on purpose as they figured the typical U.S. driver (being used to the heavy barges from the 40's and 50's) would prefer to turn the front wheels more in attempt to follow the curve.
If both spring eyes were the same distance above the ground you would develop "netural steer". Note the typical early Mustang race car has the rear eye of the spring at almost an even height with the front eye.
If you are old enough to remember seeing Falcons with weak rear springs and 18" long shackles but the rear spring eye was still lower then the front eye, you saw a car that "oversteers". Loose control in a curve and the car would tend to go off the road backwards.
Now, in the case of the Falcon shown in the photo note the position of the eyes of the front spring and apply the geometry stated above.
#2. Lack of front sway bar as on the stock Falcon. The front sway bars effects the loading of the rear wheels, a rear sway bar effects the loading of the front wheels. The idea is to load both tires on one end of the car evenly. Engine torque and the fact that as a car rounds a curve the side of the car on the outside of athe curve drops causes the axles to moveup and down/rear axle steer.
Under acceleration the pictured Falcon's engine torque would lift the left front of the car causing the right rear to drop. When the geometry mentioned above is applied the rear of the car would want to steer to the right. That 63 sedan I talk about in the "Dumb Falcon engine swaps" topic did this big time. (I should talk. On my 85 Mustang, a front sway bar mount is missing and the rear axle locator is disconnected on the right side. Been there, doing that.)
Once the is torque reduced (shifting gears, backing off throttle) torque the rear axle would try to steer the rear of the car in the opposite direction. reapply torque and the rear takes off in the the other direction. May be fun on a drag strip but a problem when driven on the highway where there are no safety barriers and vehicles are coming at you!
You CAN engineer a straight front axle/Falcon rear suspension to handle, but since these were drag cars why bother? There was a 63 Sprint raced in this area that had the body sitting level and spring eyes repositioned to eliminate the unwanted steering effects. It could be driven on the road with no more problem then one would encounter driving an early Econoline.
Last edited by yank with ute; 05-28-2009 at 08:13 AM..
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