First Generation Firebird-L Mailing List
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Tilting the rearend down for traction? Who said that. You tilt the rearend
down to make up for traction.
I came from a different school. I had learned that, especially with leaf
spring cars, there was a thing called axle wrap when the torque that is
transmitted through the driveshaft tries to turn the tires on the ground.
If you use ladder bars or a fixed four link suspension, there is minimal
(depending on how much torque and traction you have) rotation at the input
shaft to the rear end.
If you have leaf springs with new standard rubber bushings and run traction
bars with abouth 1/2" gap to the rubber snubber, then you stomp on it, do
the traction bars come up against the springs? Sure. Do the springs flex
up during this action, also? Sure. Because of this, you just added, at
minimum, +4 degrees of axle wrap to your input shaft angle. The higher the
torque and the better the traction, the worse the axle wrap gets.
What does this do when you run -4 degrees on your input yoke? It makes it
zero when you are under full acceleration. Takes the least horsepower to
move the car and does the least damage to the u-joint.
The problem is most of our driving is on the street, not the track. There
is at least a percentage of time we have moderate acceleration, then
moderate deceleration (using the engine compression as the brake). The rest
of the time is spent in static, more or less lightly loaded position.
Now, just what angle do you position the input yoke in relation to the
transmission angle when you drive it every day?
I say, not at zero. I will tilt my rearend down 1.5 degrees with radials
and 2 degrees with street drag tires. This would give me a tilted up angle
of only 2-2.5 degrees or so. I spend a little time with my foot pushing
down and I don't want to get too much positive axle wrap under load. I
split the difference, so to say.
If I was going to dedicate the car to the track, with leaf springs, 'stock
style' traction bars and slicks, oh lordy, you can bet I will be setting the
down angle at close to 5 degrees. This would be bad on the street. Most
likely, I would eliminate the flex points with lift bars or ladder bars and
use the springs to just smooth out the ride. Then I would set the angle at
zero for a 13 second car, -1 for a mid 10 second car and reinforce the
housing and be around -1.5 degree for a upper 9 second car.
Before you zero out every car out there, understand where the settings
should be for the conditions your vehicle will see. If you really want to
run zero difference in the input shaft to transmission for angle, then run
F78 x14" tires, drive only in the rain or have a turd for an engine and you
will be OK.
Rusty Allison
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