Double dip tube axle on hairpins with quarter ellipticals...

Sorry, but me too.

 

An oil tanker flexes as well, that doesn't mean you should use it for white water rafting.

Yes, hairpins do flex. I understand that. However, their primary function is north/south location of the axle. Not absorbing road.

 

Maybe when you guys are done being afraid you can elaborate?

 

My '32 had a complete Dave Gale ch***is under it with front and rear quarter eliptics suspension. It rode extremely well, more like an A arm suspension rather than straight axle. And, a bunch of miles were put on it with NO issues whatever. The front was set up like your picture except it had just one radius rod on top of the axle running rearward. The shackle mounts were welded to the bottom of the tube axle and the springs ran inside the frame rails so they were 98% undetectable. The steering was Honda Civic rack and pinion with a special Borgeson slip joint for the movement. Damn, did it not only ride good but it sat the frame 3" off the pavement. Oh, no panhard bar needed. No right to left or left to right deflection. I guess it still rides good as the guy I sold it to sold it last year at the GG Charlotte runfor over $40 large.

 

Things that don't flex break suddenly without warning and often in a catestrophic manner. Flex is needed. Managing flex is the key.

 

No, one of their purposes is locating... the other is absorbing some force... by flexing.

 

When you talk about structural member under forces, you talk about deflection in "X" direction, deflection in "Y" direction, and twist along the length of the member. It is Ok to have any two of these defections at one time on a member. It is when you observe all three deflections that you will see failure.

Looking at any straight axle suspension. you will always have deflection in the "Y" ( up and down) direction due to the m*** of the car on the axle. You will see deflection in the "X" (front to back) direction during driving and braking due to road forces. With the hairpins on a tube axle you will be introducing the twist during any travel of the suspension. Guess what you have now created a situation where all three deflections are present. You have created the "perfect storm". At this point, failure is determined entirely upon the duty cycle or fatigue cycle for the part to fail.

Now this is purly ****ytical, in the real world you may never see a failure under these conditions. But it was science and engineering built upon ****ytical design and thought that put men on the moon and in space.

Its your car and your life.

 

This new product from Posies does address allowing the axle to tilt left and right.
http://www.posiesrodsandcustoms.com/category/posies-product-releases/

 

I'm running the same wavy tube axle on my truck/modified/pil-o-parts with split bones. I made spacers to fit in the tube and welded them in, my bones fit perfect over the tube, so far no problems...

 

Pick up the new/last month Rod & Custom one of the cover cars has pretty much exactly what you want to run. I believe he's using shackles, maybe the shackles are an extra measure against bind or something, I could see the springs and the hairpins moving on slightly different arcs which may cause a binding action if hardmounted. I read once somewhere that a quarterelliptical should only go without shackles if being used as a locating member, ie. the lower part of a four bar.

 

This is my point though.... "It's your car and your life".

If this is so awful, explain why every single T bucket hasn't killed it's owner yet?

I was kinda hoping a bunch of people who have personal experience with tube/pin combos would reply.

 

I've seen many instances where an engineer says,"It won't work," but somehow it does. Actually several folks here (IBB41, IRS30)have said they did it and it worked. I'd go for it, but drive it on some back roads to test it.

 

I think that's a bigger concearn than the hairpin and tube axle combo cauing the apocolypse.

Oh, and one other reason I would like to do a front end as such... because it's a challenge, and everyone says it can't.

 

You can't compare the suspension of a 1400lb bucket to to a 2800lb or more coupe/sedan. That 1400lb difference stresses the axles completely different. That 1400lb's cause less deflection in "Y" due to less weight and less deflection in "X" due to reduced braking/road forces. The twisting forces still remain the same based on the amount of suspension travel no matter the weight of the vehicle.

Do you put the same springs under a "T" as you would a full-fendered coupe? No, why not? If you need stronger springs under a car because of additional weight, where does that additional weight end up? On the axle! The axle will deflect different based on the m*** or forces applied to it, period, plain and simple. The forces observed by an axle under a T bucket are entirely different than the forces that the same axle will observe under a coupe or sedan.

A T-bucket can get away with it because the axle is stressed less in "X" and "Y" while keeping the same amount of twist. How is that for an answer. Remember it is the combination of all the forces that is the axle killer.

Everyone can tell you what to do and what not to do, but in the end you make the decision based on what works and your knowledge. The difference is that some people listen and some know more than others.

 

here is a pic of what i started with...i need to take some updated pics

 

The only thing I could see maybe happening, is that as the springs flex it might want to rotate the axle, which is solid mounted by the front of the hair pin. When the springs flex they get longer and shorter, which something has to give to compensate for the movement. In the drawing the shackles would provide this as long as they don't bind against the axle.

 

Richard D,

Engineering is a great field to work in. Did you know that you can pick up a 2500lb car with a 3/8-16 grade 5 bolt? From an entirely imperical approach the bolt tensile strength is such that you can do it, doesn't mean that any engineer worth a dam will tell you to do it, and I highly doubt you will find one to let you do it. Engineers will tell you it will fail but you can do it, I wouldn't try it. when engineers tell some one that it won't work or shouldn't work listen. Engineers are trained to take in consideration something called SAFETY. But then again sometimes people know better than engineers and just don't listen.

 

I agree with this allthough my bucket weighs 1840 lbs with 960 of it on the front axle and 880 on the rear.

 

1) Still waiting for an explaination of who T buckets haven't been killing people for 40 years.

2) You're ***uming this is going on some "1400 pound sedan". If you re-read you'll notice something... I never mentioned what it's going into.

FYI: It's a short ch***is "modified" setup running a 34' Ford pickup cab. No box, no fenders, etc. Weight? I'd bet it will be damn close to 1800-1900 pounds. That's it.

So in response, yes, I can compare it to a 1400 pound t-bucket.

3) Someone once said something very impressive: No matter what you know, someone knows more.

You can give me an engineering opinion, and that's gravy, but it's completely differing not only from the experiences of those who have responded that ARE running a simlar setup, and those who have been running it for the last 40 years.

Thanks for the replies though still!

4) "But then again sometimes people know better than engineers and just don't listen."

Sarcasm will get you nowhere.

 

IBB41,

If you really want to test the twist theory, go out to the shop and draw a long straight line on the top of the axle while the car is sitting on a level surface. Now jack one side up until the other just begins to lift off the groung. Now using a level, string, and and some help run the string directly up form the front or rear of the axle and observe how much that axle has twisted due to the suspension travel.

You will see a twist. The amount of twist will vary depending on the type and strength of your frame. So now you can see the deflection in the "Y" direction due to the weight of the car on the axle and the twist due to suspension travel. Well this is only two of the forces we are talking about. The third comes in only dynamically when the car is being driven, it happens only during driving and stopping.

 

The exact words from a suspension tech that I spoke to about this today?

"Yes, what these guys are saying is true in the terms of the physics involved, but in the real world driving situations it's damn near moot considering that you're driving a hot rod with a few inches of travel and not a baja racer with 2 feet of travel".

Engineers may be able to talk engineering, but I'll take word from a hot rod builder that specializes in this stuff first...

 

it's not about if the thing under stress will flex, it's will it flex enough.. there's a difference. if a tube starts to flex and hits it's limits.. the force goes to the welds.. the joints.. everything else.. it has to go somewhere.. just find a place in the system that will give enough to take whatever you throw at it.

 

First off I am not being sarchastic, it is just the truth that some people know more than others, while some just don't listen. I have never proclaimed to know more than everyone else. I am just a Hot rod builder who happens to be an Mechanical Engineer.

This guy or suspension spe******t take a paycheck from the company you are buying stuff from. If the company doesn't sell stuff, he and others are out of a job. Of course he will tell you it will work and he is right. It will work. It will also work for a long time. But it will also fail at some point, not today, not tomorrow, not next year, who knows when. Everything that undergoes repeated cyclical motions will fail from fatigue failure. The situation of forces you have placed that axle in will accelerate the fatigue failure, thats all.

You can do what you want, you came here and asked for advise and I replied. Thats all. I gave you my engineering opinion. Listen, don't listen I don't care. Again, it is you car and your life.


I am out, done with it.

 

I was kinda hoping a bunch of people who have personal experience with tube/pin combos would reply.[/QUOTE]

Did you not read my post earlier?

 

Again with the ***umptions. I clearly stated earlier in the thread that I'm not buying anything. I build my own stuff. See, I happen to be a professional welder/fabricator. So this idea that someone told me this or that to make money is BS... especially considering that the first thing I said was that I DO NOT plan to buy anything, but would like to talk some shop if he had a minute.

And again, that makes sense on paper, but where's the failure of all the T-Buckets?

 

Yes I did... and your post single handedly made me come to the conclusion that this is possible. Which is why I'm going to do it.

Any pics of that setup?

 

MPLS...did you check out the Dave Gale setup that someone else mentioned?
It's cool and neat.

Working off that hidden 3 point setup, you could make it a 4 point...still mount the 1/4 E's without using shackles as the lower locators and run an exposed single link on either side...kinda like half a 4 bar setup on each side.

That would get tongues wagging as people tried to figure out how come the axle doesn't flop with only single links per side AND twist on the axle would become a dead issue.
For all intents and purposes...the setup IS a 4 bar so there is no real axle twist as the suspension cycles. With well designed spring mounts I don't see why you would need a Panhard but its easy enough to add if it made you feel better about things.

That's the style of suspension I'd look at because its safe enough and unusual at the same time.
You wouldn't need to run a R&P like Dave Gale did either...

 

I would probably run the shackles as you already have 2 points on the axle keeping it swinging in one plane...if you add the spring as a 3rd pivot poit it must also follow the arc of the fixed hairpins....but as a spring flexes it tends to change length slightly therefore creating a binding situation. Harlan from down near Paso was on here years ago and designed a front setup pretty much just like yours and he ran into what I am describing. He decided to elongate the holes in the brackets for the springs as he ran no shackles...grade 8 bolts and he drove the piss out of it. (He also designed his own intake that a bunch of people said would never work....proved them all wrong on that also)
OOOOR I would probably just use the spring as a lower link....I did that on a lightweight vehicle I built...triangulated the upper bars and ran it. Rode nice...oh yea, that was on the rear.

 

Yeah, I'm trying to find pics. I think that makes a lot of sense though.

A 4 link, using the springs as the lower 2 of the 4. Seems like it would definitely be something you don't see every day. I want the front to be odd like the rear end.

 

That was my other main concearn.

If the springs are, say, 18" long to axle they will sweing a tight arc.

The hairpins on the other hand will swing a shallow arc.... which is a recipe for bind as the arc difference would be enormous.

If the shackles were setup right they would be in tension at rest and compensate for arc difference in travel, right?