Im in another phase of my 1951 DeSoto Sportsman hardtop project.
In 1979 I installed a 9" Lincoln rear with discs and sway bar on the stock DeSoto leafs.

The goal for the current revamp is to get the car to where I can reenact my 1975 visit to Mexico in enough comfort to convince my bride to accompany me. This means EFI and a larger fuel tank......and more trunk space.

I propose to change to B body leafs and sliders. I want to move the springs outboard 2" to make more room for the tank and a deeper trunk floor.

What effect would moving the leafs outboard 2" (a side) have on handling? The car has a 75 Satellite cop car front suspension already.

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

Moving the springs outboard will increase the roll rate.

_________________
Joshua

Im not sure what increasing the roll rate means.....

I have a 3/4" rear sway bar.....will moving the springs make that overkill?

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

You will have more roll (sway) stiffness with the springs farther out, so yes, the bar might become unnecessary. 2" a side sounds like a lot - great. I would road test for neutral handling before re-engineering/installing the rear sway bar.

Sounds like a fun project!

Lou

_________________
Home of Slant6-powered fun machines since 1988

The Ford axle is wider than the original axle. I have a full 2" a side available. I just have to move the perches on the axle .

I plan to use a new AFCO hanger in front and a slider in the rear. The slider will be mounted on the outside of the reinforced rear frame section.

Room for a big tank and trailer hitch are the goals.

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

Happy fabbing!

Lou

_________________
Home of Slant6-powered fun machines since 1988

Mr Speaker...a supplementary question from the member for Valkyr Range and the Lake.....


What is the effect of mounting leafs in a non-parallel configuration,,,,,ie closer together at the front than rear? Towd-in ....a small amount.

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

Josh might be able to answer this better than me. I have not thought about this in detail. I know E bodies had this from the factory, maybe 1-2" from front to back?

Lou

_________________
Home of Slant6-powered fun machines since 1988

Straight axle pickups were this way up front from the factory as well. No idea if/how it changes suspension geometry though.

_________________

Here's a link; it's not great, but it hints to the effect: http://www.afcoracing.com/tech_pages/leaf.shtml Look at the last couple paragraphs and diagram at the bottom. It says what effect should be expected (care feels 'tighter' to the driver), but not why.

Tom Condran talks briefly about this in his book. I thumbed through my Carroll Smith and Fred Puhn books and didn't see hardly anything about leafs.

My understanding is that the effect has to do with how the spring moves through it's arch. Envision the unequal length springs of a Mopar suspension. Generally, the front spring eye is mounted lower than the read. If you think about the angles involved, this means that under load (ie, cornering), the outside tire is more heavily loaded than the inside tire. Thus, the suspension is compressed more on the outside than the inside. Think about the axle attached to the spring under these conditions: The outside leaf compresses, and the axle follows the arc: it moves away from the front spring pivot. The inside tire at best stays neutral, or more likely arcs downward, bringing it closer to the front spring pivot. this has the effect of pointing the rear tires to the outside of the turn, which increases OVERSTEER.

When you 'toe-in' the leaves, you have to consider how it effects the rear axle. I think that more 'toe-in' on the leafs increases the over steer characteristic. A little is supposed to be beneficial, but like most things, too much is bad. Stock A-Bodies have the springs toed in slightly.

And, in answer to the other question, moving the springs outboard will increase rear roll stiffness, ie they decrease the leverage that the body/frame has on the springs. It effectively increases the spring rates. When you increase the roll stiffness of one end or the other of a car, you increase the effect of that end... stated differently: more rear roll stiffness means oversteer tendencies, more front roll stiffness means more understeer tendencies.

So, if you move the springs outboard and keep your current rear bar and leave the front end alone, you should have more oversteer in the car. Whether or not this is too much is really up to you. If it is too much you can either go to a smaller rear bar, or a larger front bar to restore balance (possibly stiffer front springs, depending on what you want).

Since it has the effect of increasing the actual spring rate (you gave the springs more leverage over the chassis), you may also find that the rear is too stiff. (in theory).

I'm sure someone understands this better than me and can chime in, but the key concepts are:
-Consider the leverage that the chassis has on the springs (effective spring rate/roll stiffness)
-Consider the motion of the axle as it traverses the arc defined by the front spring section under load.

Thankyou Mr Polara!

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

Rear leaf spring toe-in is actually supposed to make the car "tighter" or less "loose" which means a softer/lower spring rate. Since you are moving the leaf springs outboard and increasing the spring stiffness in roll you can counter some of that with leaf spring toe-in. E bodies and late B bodies had the springs with toe-in.

How much difference are we talking between the front and rear? An inch on each side?

_________________
Joshua

We are talking about a max of 2" on each side .(outboard at the rear of the spring .....compared to the stock DeSoto spring

The front suspension I am using is late B....and the springs I plan on using are late B.

Time for a walk out to the pasture to measure my 78 Fury ........


The Desoto is 126" wheelbase with the engine set back 12" from the front axle centerline (stock).

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

Well...it turns out the 78 Furry has parallel springs as does the DeSoto.

The B leafs are longer 24/33" vs DeSoto 24/28"

However the amount I wish to move the spring outboard would make the spacing the same as the late B......on the rear

As I have less "room" to move the front hangers outboard I will end up with about 2-3 " toe - in (total) 43" front / 45 - 46 rear.


My Early A has parallel springs 24/34"

The early Dakota has parallel springs very similar to the late B ....but they are 3" longer.24/36"


A survey of GM products on hand shows no leafs with toe in/out.

My 69 Dart is too low to measure.....

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

http://www.afcoracing.com/tech_pages/leaf.shtml

Its all right here.

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....