Hot Rods Tranverse Springs Tech Info.

Well, I guess it all starts at the chassis contact point, with whatever system is being used to attach the spring to the chassis.
In the case of the front spring, it is necessary to achieve a caster angle which should be built into the cross member.
I suggest about 6 degrees but any rake of the chassis can steal that 6 degrees away from you.
I'm sure many a hot rodder has gotten his caster angle built into his cross member only to discover it has been lost later in the project when it has all the weight and tires fitted.
So stance needs to be considered very early in the project.
What should be don't when it comes to the rear cross member???

 

Yep,
But at least there’s 4 of them...........


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And the shackles are double sheer, unlike a lot of coil over mounts.


Phil

 

Eaton Detroit Springs is the best I've found with regards to 2nd leaf length. And honestly, with suspension components, it's not worth trying to save money by using cheap parts, especially if you intend to drive the thing. There was a comment above about stock springs with regard to looks and 2nd leaf length, and Eaton is the only manufacturer I've found that has near-as-makes-no-difference springs to the factory. Helps that they've been supplying OEMs and aftermarket for decades.

I don't know where I'm going with this...

Mike

 

All you gotta do is have one go and there goes your day.

 

Greatly depends on if the rear bar mounts are welded on the rear or what type your using.
Personally I won't start a chassis build without the wheels and tire to be run already here.

The "assembly" of axle and spring sets at the proper angles, caster & pinion.
The assembly moves back or forward to establish wheel base.
Drop the crossmembers on the spring pin, clamp crossmember to that spring set at that assembly angle and your established. Connect the front cm to the rear cm with rails. Doing it that way ride height is built in, stance is built in, and it works.

 

I don't know what Speedshifter's load bolts set-up looks like; but on track cars, they just made a hole in the top of the crossmember, welded a large nut on, screwed a bolt in to push on and preload the spring. On the right side, sometimes with a ratchet welded on the rear one for "on the fly" adjustment.

 

31Vicky, I like your process.
I assume that this would also eliminate/minimize any binding of the spring.
I suspect spring bind is quite easily built into a front end using radius rods other than stock configuration.
Probably more by accident and ignorance than intended of course.

 

It works well, but you do need everything there. Guessing at what might be or anticipating changes within a forever build time frame ,,, well that crystal ball might be a better way to do it.

I'll tell you for sure, building a car to set level is quite different than building a car to set at a rake. Throwing a rubber rake on a car that's been built set level causes differences & Some of those differences are problems

 

Rich B Yes, that is exactly what I was describing. The nuts welded to the cross member were 3/4" 10 TPI & were 18" apart. Did not post photo as my computer skills are horrible. Worked great for me.

 

Anytime you shorten a spring,,, either by cutting it, chopping coils or altering the effective lenthg - (like these stop bolts) you make the spring stiffer.
If that stop bolt is 7" away from the U bolt you've shortened the spring by 7 ".

A transverse spring is sort of like a double ended 1/4 elliptical.

 

Actually realised that I was wrong,.............there’s 8 of them......twice the strength........

 

Not much difference to the size of a center bolt head that largely resists sideways movement.
Then why are U bolts so large when compared to the size of shackle bolts???

 

Just amother one to ponder right?
Study it and you can see why ubolts need to be good sizes. Then let er rip on shackle bolts that appear to do a lot more work.
Most parallel leaf springs we see here run 9/16 bolts.

 

While I agree with your comment, really the centre bolt is just (in theory) holding the leaves together, with the U bolts stopping all movement of the spring pack.

 

I also wonder if the 3/8 shackle bolts were quite adequate for 85 hp early Fords, yet is something that has perhaps been overlooked as hp has increased over the years.
But then again, how often do you hear of them breaking ?

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From my limited knowledge of front or rear end failures, generally it has come down to poor installation or lack of knowledge rather than component failure.
However, one must wonder how these simple and basic components have been able to handle both additional HP and torque with some very heavy engine power plant weights to boot.
Maybe it is that our roads are better these days and less demanding...

 

Subscribed
Thanks everyone!

 

I see this thread as a forum to discuss and share information regarding transverse springs with a specific focus on our hot rods.
While most of us still use the original cross members as our mount point, many hot rodders over the years have come up with different takes on how to mount a transverse spring at its center point to the chassis.
Probably the earliest use of homemade mounts were born as the T bucket evolved and radius rods were split.

 

So here’s a question;
Why are U bolts always used as a pair ?
Why not use a single U bolt in the centre ? - The bottom plate could go over the centre bolt.
To my way of thinking, that would be less restriction on the spring pack, and allow it to work better.

 

As I expressed previously the size of U bolts in relationship to other suspension related components which appear to be lighter and exposed to a lot more stress than U bolts ponders my thoughts.
There can be quite a lot of metal found at the attachment point where the center part of a transverse spring meets the chassis.
Obviously the idea is to sandwich the spring between the supporting cross member and the compression plate by using the 4 U bolts and yet the principle still relies up the center bolt as a kind of key to ensure no possibility of position shift.
I am unsure whether it is something to do with the characteristics of spring steel that demands the sandwiching rather than a direct thru hole bolting method using the center bolt or similar.
The other thing that comes to mind is, are 4 bolts and a compression plate some how required to transfer the twist load that is generated during suspension movement and maintain a strong link between chassis and spring.
I assume in a boxed chassis hot rod the chassis is transferring anti twist resistance back to the spring.
I suspect that a single center bolt used to hold an entire contact between chassis to spring would firstly not be strong enough and secondly not provide enough stability in the connection.
A third consideration is that after speaking with an old black smith friend of mine who used to make springs, his comment was that the wrong stresses would fatigue the center bolt which was used for a different purpose and the holes thru which the center bolt passes in the spring steel will become a certain weak point and be vulnerable to cracking.
I really would like to be hearing from some of our serial experts who are usually present during discussions like this.
The first name that comes to mind is Ned Ludd.

 

Yes, I also thought that there would be more interest on this thread about such things......
BTT

 

You need the pin's head it does one job, you need the center bolt it does another job. First job they do is act as alignment tools for assembly, then they do the job again in service duty and again in disassembly.
One spring center bolt does 2 jobs and 3 shifts if you will and at the correct time.

Sometimes guys will put a spacer between the springs and crossmembers to get back some ride height. The spacer they make has a hole for the spring pin but they forget about adding the pin to the spacer for the crossmember. Spacers I make have the pin too.
I've seen the pinless spacers get a bunch of miles before they show symptoms of shifting, but they do shift eventually. So the job of the pin is small but very important. It gets the "assembly" of spring and axle centered and keeps it there. The clamping force of the unolts is great, the friction between the crossmember and spring/spacer is great as well.
The springs dynamics are equally powerful. Think of 2 equally matched powerful wrestlers, the Friction and the dynamics of the spring. They lock up and battle for superiority. We want the friction to win and control the spring, so by adding a tiny centering pin to fiction the wrestling match is no longer even and will always go to friction and keep the spring right where it supposed to be.

Assembling, well I couldn't imagine assembling a spring without the centering tool aka pin. Let alone trying to get the spring/axle assembly installed in the car with 5,7,10 loose leaves. So let's just bolt the spring together and make that part easier. Great,,, but now we have a bolt head right in the middle of the spring, so poke a hole in the crossmember. It will keep things together.

There is another problem with the springs hole. There should be no movement of the spring Near the hole because that's a prefect place to break. The Ubolts on either side of the hole create a zone in the center protecting that hole from seeing movement provided they are tight and fully compress that spring to full contact.

I love parts that perform more than one function.

 

My observations, from my perspective, thru my jaded view filters, and from my side of life say .....

that not many get past the catalog directions and order a spring. Put the stuff together off of the paint by numbers directions and roll with it.
Maybe some get further in and try to figure out why their stuff doesn't work.

I'd say most guys "know" their shackles should be at 45* but not many know why. Or that it's just a quick visual reffence check to show you that a stack of variables is correctly reconciled.

I'd also venture to say that not many know why their shackles may set at 50* instead of 45, or 40 instead of 45 or that shackles closer to 90 pose special problems to control.

I've seen some who reverse springs, re arch them, remove leaves to get lower ride height and can't figure out the spring get longer EYE to EYE when the free arch is lowered. I've yet to see a cataloge list the critical dimension of free arch height at installed (under preload tension) length.
We can have 101 different springs with EXACTLY the same EYE to EYE measurements, and everyone be made from a different length main leaf with a different arch height. For example at an extreme it's quite easy to have a pile of springs with 30" Eye to eye and have the arch height vary anywhere from 4" to 40', yet all will be in the "length 30" category.

There's a lot involved, it's like the spokes of a wheel.

Again, just my opinion and it may not be correct.

 

Love your opinion 31Vicky and it is so true.
As you say there is a lot more involved in springs than meets the eye.
Hence, this is what prompted me to start such a thread.
I am surprised at the lack of participation to date...
The silence is deafening.

 

I think the trick is to see a transverse leaf spring as if it were two completely separate quarter-elliptic springs, mounted heel to heel, as it were. If we then consider one of these quarter-elliptics in isolation, it's a simple cantilever beam problem. You have a beam with two supports close together and a load at its cantilever end. The greater the distance between the supports, the less the stresses at those points.

The first problem with a single central bolt alone is that the effective distance between the supports is effectively halved – in so far as the distance can be determined at all. It could work if we introduce ribs or frets on the underside of the crossmember to form positive fulcra for the spring to bear on. But now, what we're doing when we ultimately morph our two separate quarter-elliptics into a single siamesed spring is that we're making the springs share one support, so that each half will need its own second support, which at any given level of stress doubles the width of the support arrangement, making us need either a longer or a softer spring. Using two U-bolts means that our siamesed quarter-elliptics share both supports, but in reverse order: the end support of one quarter-elliptic is also the middle support of the other, and vice versa, and we don't need a ribbed mounting. It's simpler, more elegant, and doubtless considerably cheaper.

Not being able to see those siamesed but conceptually separate quarter-elliptics leads to all kinds of misconceptions about the geometry of transverse leaf springs. The suspension does not roll about the point where the spring bolts to the frame. If anything moves relative to anything else at that point, your suspension is at the point of failure. How the suspension does rotate in roll is somewhat more complicated than you'd think. I've explained it a few times in that past, e.g. here: https://www.jalopyjournal.com/forum/threads/anti-roll-bars-on-the-front-end.746645/#post-8307931 and here: https://www.jalopyjournal.com/forum/threads/i-beam-vs-ifs-pros-cons.470069/page-2#post-5250366. Going back through those threads I'm reminded that it's not only complex but also controversial.

But the point which comes out of that is that the importance of the angle of the spring shackles is that the shackles constitute a lateral-locating device. The minute you have another lateral-locating device, you really want to eliminate the lateral-locating action of the shackles as far as you can. The minute you have a Panhard bar (and a dead perch turns half the spring into a Panhard bar) or something less common like a Watts, WOB, or Mumford linkage, or even a triangulated 4-bar, you'll want the shackles as close as possible to tangential to the spring action, i.e. just off vertical, or the closest you can get to that without the spring eyes colliding with the perches etc.

I just had a thought. If the vertical distance between the roll centre defined by the lateral-locating device and the instant centre defined by the shackles is large, lateral forces can only be resolved by flexing the spring. In that case it might in theory be possible to use the spring as an anti-roll device, or even to induce positive banking. I know what's going to keep me awake tonight ...

 

Fiat 600 IFS, 1955-1969:

Note that the centre of the spring is bolted together but not bolted to anything else. This makes the spring deflect in a soft U in bump but in a much tighter S in roll, resulting in effective anti-roll action. Pretty much all the small rear-engined Fiats used this arrangement, and Fiat later adapted it to the rear of the front-wheel-drive 128.

Many subsequent transverse-leaf independent systems have used this dual-fulcrum principle. It's quite clear in the Corvette pics above.

 

Thanks Ned for expressing your slant on this topic.
Your comments have cleared a few question marks up for me.
Boy, I must have lived a sheltered life not to have ever noticed the S style transverse spring setup.
It is a very interesting concept.

 

Is there a right or not so right way of compressing a spring at its point of attachment to the chassis???
Is it better to use a one piece compression plate compared to what you see in the pic below?

 

Thanks to everyone who has posted, some interesting information here

Bobby