Hot Rods Underslung front suspension

I am in need of a supplier that can help me put together a front end that will work with an underslung approach. I live in Spokane, WA, where Pohl Springs is HQ'ed and they are adept at coming up with 2 springs that will work....I just need someone who can put together the front end? I have been trying to get a front axle/frontend from a supplier out of Oklahoma....name deleted on purpose and have not been able to get a resolution and I need to get this done ASAP! This is picture of a frontend that would be very similar to what i need. Any suggestions/help would be greatly appreciated.

 

In case you didn't know, leaf springs are not designed to work upside-down. Best of luck with your project.

 

You want a plain straight axle? How about go to the Walmart of hot rod parts: Speedway Motors. Order up a "gasser" kit, even available complete with all the spindles and brakes if you like. Toss the regular springs and use your upside down springs.

 

You should really research " Underslung " chassis / suspension.
The chassis in the pictures you shared is not a good example of underslung suspension.
Those springs are not going to work very well.
The guys that pioneered it knew what they were doing!
You should strive for something more like these examples!

 

Looks like it would be very unforgiving. How much does it move if you jump on it? I know I'm not answering the op's question but I'm not understanding how this would work.

 

Consider scrub line. It looks like a strike, without a load or bump.

 

Well we most likely know that "supplier in Oklahoma quite well and if you sent that photo to them not getting much of an answer may say that they don't want to be involved in your mess. They drop and repair I beam axles but don't do anything tube axle wise. As Pete said, you need to hunt for a Tube "gasser" straight (no drop) axle from Speedway or another tube axle supplier. This axle can be ordered in several widths or a custom width and uses 51/54 Chevy car spindles. Normally a straight axle gasser (as in Jacked up 55 Chevy) axle Speedway Heavy Duty Gasser Straight Axles, Chevy Spindle (speedwaymotors.com)
Your spring will somewhat work but will be like a very worn out pickup spring or a spring that someone took too many leaves out of like the spring in my 48 where I removed a bunch of leaves to lower it with the intention of driving it to two events and then taking the truck apart and redoing the suspension but instead drove it for 15 years that way. A filthy mess because it was my daily driver for most of that time in all weather and on all roads. note that the "failed" spring has somewhat the arch you are looking for but the leaf stack is in the orientation that it has to be in. This is how your leaves need to be stacked even with the curve going the other way.


First study the photo and images of The American underslungs that Pete showed and study this link The American Underslung Speedster, pt. 2 — ClassicSpeedsters.com Take serious note that the springs are still in the same orinentation that they would be if they were under the frame. The frame is under the axle hence the Underslung concept but the spring is still working the same rather than being positined as is if you just flipped the chassis upside down.

This little T that I found on the net has it set up about as close to right as a hot rod underslung is going to be. take a close look at the orientation of the springs.

Bottom photo is a late 20's Chevy frame that I have for my boat tail roadster project. if you flipped the frame and then bolted the springs back on in the correct orientation that they were you could run it as an underslung frame as my dad said he and a buddy did in the 30's. You would have to take the front and engine support crossmember out and flip them to support the radiator. Then you have to run real tall wheels and tires.

 

Yep springs ain't gonna work upside down. Springs work by being compressed not by pulling apart.

This is one of those idea's there of someone who has no idea of spring movement or spring loading.

.

 

Ya could just flip the whole works over..

 

Have a good look at the photo that @WRMDOVR posted! The stack of leaves have been reversed.[It will work OK]

 

https://www.jalopyjournal.com/forum/threads/underslung-rods-thread.565759/


I like the rear setup. The front?
I really dig the car but I’m curious on how the front setup does

 

Ok. Cat amongst the pigeons time.

Question: Would his setup work using a mono-leaf spring ???
Answer: Yes, I think it would.....

Question: So, would it work if the shorter leaves were stacked in the concave side on a multi-leaf spring ???
Answer: Yes, I think it would..... (although it would take some doing to make it function correctly)

Now, take a closer look at his pic, especially the rear of the right hand spring (left side of the pic).
Looks like a reverse stacked leaf pack to me.......
Maybe the concept is sound. The actual execution would be a bit of a nightmare though.

The Jeep Cherokee 2WD front axle has to go though...........

Damn @Kerrynzl , you type too fast.........

 

My "one finger typing" was 17 minutes before your reply

 

Yep, I am super slow. But, in my defence, I was searching for a pic of a reverse pack spring. Not many pics of that on the googley machine...... No, honestly, that's what took me so long............

 

Nope, putting spring pack backwards won't make it work. You have no ability of the spring to flex under load, leaf springs absorb the load by becoming longer not shorter, in this configuration under load they would have to become shorter.

Look at every picture posted above, the spring and pack are designed and made to expand under load. The factory setups shown above wouldn't have went to all the trouble of the designs above if it was as easy as just turning the spring over.

There is no lower kit, oem, or aftermarket company that makes anything to either lower or from the factory that has an upside down spring on any make of vehicle even to this day for the simple fact it won't work as a spring is intended to function.

.

 

Expanding or Shortening linear length under load will only effect shackle angle.[this needs to be factored in the construction design]

As long as the main leaf is on top and the others are stacked underneath it doesn't matter if the leaves curve upwards or downwards.
The stacked leaves need to be under compression [not tension], so the exact opposite applies to cross-leaf or quarter elliptic springs where the centre-bolt is the point of chassis mounting.

I have reversed a leaf pack in the past [then flipped it] and measured the spring load in a press . The results were exactly the same lbs/in .

The spring rate stays exactly the same [lbs/in] it is only the spring load [shape] that is changed.

 

What about transverse springs, they are mounted like his?

 

The OP's picture of his spring set up might work, but with the arch of the spring, bump steer would be pretty scary. How would you keep the axle from moving forward or rearward going over a bump with only one wheel?
The more straight the main leaf would be, the better his underslung suspension would work. To straighten the main leaf, either the front or the rear spring mounting points (preferably both) need to be raised up. The more straight the main leaf on that setup, the less effect the bump steer is going have. With the rear spring having about the same arch in the main leaf, the rear axle will also be moving when one side encounters a bump the other side doesn't see. That car would be a nightmare to drive on a bumpy road, both axles could steer the car without any steering wheel input. With that in mind, if I ran a spring shop, I wouldn't supply springs either.

If the OP wants to do underslung springs, he needs to build the frame so the main leafs are fairly straight in their as driven condition.

 

But in a common transverse setup the ends of the spring are mounted to the axle, and the centre to the frame, so on a bump the spring is straightening/extending, and on rebound the spring is arcing/shortening. With the setup shown this process is reversed.

 

Roll steer only affects the rear axle because the rear wheels are always perpendicular to the axle.
The front end usually parallelograms itself [steering correction] unless bump steer hasn't been engineered out of a bad design.
I am not fond of high spring load suspension [deep arch leaf springs] because of this issue.

A better design for underslung deep arch springs would be to "float" the springs by having a shackle at both ends.
Then use a trailing/leading link to locate the axles, keeping the link as close to level as practical.
The leaf springs will still control rotational torque of the axles.

This ^^^ sort of arrangement was common in road racing where the regulations required original style springs.

 

early/mid 70's front springs on a 4 wheel drive Blazers

 

I put a little 1 person roadster together back in the 80s and underslung the front suspension using 36 chevy pickup front axle and springs. Reshuffled the spring leaves and included the original 36 shackles. I never got it on the road but a friend did and he drove the shit outta that little car. Ran a 235 Chevy in it.

 

Does this mean you stacked the shorter leaves on the concave side of the spring?

 

Guys, just because you put the spring pack on the inside of the main leaf doesn't fix the engineering problem of using the spring the opposite of how the leaf spring was engineered, as an example, let's replace the leaf spring with a coil spring, on an underslung frame you would be using a coil spring under tension instead of compression. (see what I mean?)

 

Someone better tell this guy it's not possible........





And here is a little something thanks to HAMBer @Johnny Sparkle

 

Ground clearance is a secondary issue, The American Underslungs had serously tall wheels and tires.
I'm not sure that I could get away with it with my frame and a straight tube axle and the 18 inch 30 something Chevy wire wheels I have. I can see wheeling into the Washington state patrol inspection station with the whole frame below the scrubline, That wouldn't go over well.

 

I'm late to this party. I'm also battling some insomnia, so take this for what it's worth.

Just because early cars seem very rudimentary by modern standards, that doesn't mean there was any shortage of engineering and R&D that went into making them. Early designers and engineers were bound by the same mathematical equations and laws of physics as their modern counterparts.

I mean... just because the pyramids might seem like little more than big piles of stone, the fact is, the only reason they endure today was because of the careful mathematics and understanding which developed over several millennia.

If factory underslung cars we're all built by placing the springs in a certain orientation, it's the result of careful understanding and years of trial and error.

I'm not going to eat anybody's hat or anything, but I'm going out on a limb here, and say that based on what I've observed over the course off my longrunning affliction with cars, no automaker that produced underslung cars ever mouthed the springs in the configuration the OP's car displays.

Another fine example of an American made underslung is the 1914 Norwalk Underslung Six.






And, as you can see, the springs are mounted with the load of the axle pushing up on the outside of the arch, just like a conventionally slung chassis.

Lets go ahead and overlook things like rotational torsion and whatnot and just focus on how the spring works under weight. When the load presses against the spring, correctly mounted springs spread the arch out lengthening the distance between the eyes, whereas in OP's configuration, the springs would be pinched inward, shortening the distance between the eyes. D'you see the problem there?

I mean... you can bolt anything to anything and it would "work", but only right up to the point where IF you have to make any quick corrections the springs would unload, you'd break traction, and go careening off into a ditch, telephone pole, or a family of six in a minivan or something. Hell... maybe all three.

Look all I'm saying is two things.

One: To quote a wise, spacefaring engineer from the future... "You cannae change the laws of physics, Captain"

And two: if OP's set up really worked, you'd see well more than just a few examples here and there on the internet.

Unlike what @anthony myrick usually says... I wouldn't drive it.

Night y'all. I'm gonna go try and sleep. I hope playing out scenarios in my head about the moments leading up to disaster with this kind of setup doesn't keep me awake any more than I already am tonight.

 

Spring steel elasticity works both ways . If the spring was mono-leaf and dead flat when static it would still arch upwards the same distance regardless of which way it was installed [and this whole thread would've died a natural death.]
If a multi-leaf spring was reversed it would behave like a softer mono-leaf UNLESS the spring stack was reversed. [the leaves "fan apart" and only the main leaf is load bearing]

A coil spring has the same stiffness under tension or compression, but there is engineering issues of holding it in the spring lands.
And to add to this , a torsion bar can be reversed [it is common to swap L to R torsions in race cars with splined bars]
A coil spring is just a coiled-up torsion bar.

Coils, Torsions, Leafs all have the same properties. The longer they are, the softer they are. The larger the cross section, the stiffer they are.

Is the OP's example good engineering ? probably not . I can see plenty of other issues there.
If I desired an underslung frame hotrod I would fabricate IFS

 

Two ways to make what you have there work much better is to use a flatter spring pack with the main leaf on the top and mount the axle on the top, i don't like the whole setup but that's just me and maybe a few others. JW

 

Not really much different than a de-arched/reverse arched spring. My bigger concern would be the scrub line issue......