[wolfman]

I hope someone can help. I have 2 sets of leaf springs both of them are '71 Challenger V8 but they have different part numbers. One pair has 3400044 the other set has 3402344. Can anyone tell me the difference between them. I am also thinking of taking a leaf from one set to add to the others to beef it up a bit, does anyone have any advice which leaf to use from the spare set? I would think the main leaf would be too much. ANyone got any bright ideas, greatly appreciated.

[dave-r]

I don't see those spring part numbers in the 1970-71 parts manual.

The way to measure a spring rate is to stand the spring on both eyes so it is arching up.

Measure the height of the spring arch from the ground up.
Now stand on the spring with all your weight and measure again to see how much the spring compressed.
Make sure the spring is on a surface that will allow the ends to slide out.

Now all you need to do is weigh yourself and find a calculator.
Your weight divided by the amount the spring compressed will give you the static spring rate.

Add or remove leaves to give yourself the spring rate you require.

If you want to be scientific about it the rear roll rate is determined by multiplying the static rate of the spring by the motion ratio of the rear end.
The rear end motion ratio is simply the center to center distance between the spring perches divided by the center to center track width (centerline of the tyres).

From this you should be able to work out the percentage of front roll couple and compare it to the percentage of front weight bias so you end up with a car that neither understeers or oversteers.

Hope that helps.

[wolfman]

Thanks very much for that Dave ,I will have to do me some sums now Then it's onto bench testing the 360 I have picked up to see If it is any good