Technical Question concerning heim joints *x2couple pics*

It is only vertical loads of a shackle, all lateral loads are controlled by a triangulated 4-link.
He wants the Heim for articulation so the 1/4 elliptic spring stays in phase with the frame

Any minor lateral movement [Arcing due to trigonometry] will be absorbed in the rubber spring eyes

 

In your drawing the weight of the car will put a bending load on the threaded shank of the rod end. It will be trying to bend the eye downwards. The load should be a straight pull of push in line with the shank. Turn the nut you have welded to your bracket vertical so the rod end shank is vertical.

 

It appears that the weight of the car is totally supported by the ' heim' joint shank in shear , not tensile as was intended. IMO

 

@2OLD2FAST yes, I get what your saying, that's why I decided to run the heim straight up and down instead. The nut will be welded in a vertical position instead of a horizontal.

Thank you for your feed back.

Thank you all for your replies, thoughts and suggestions!!

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Barring extraneous factors, shear strength equals tensile strength. But we're dealing with a bending moment here.

 

I must be missing something,
Shouldn't the front spring be solid to the frame?
Whats holding the leaf pack together?
Wouldn't a longer spring would solve a lot of problems?

 

@Joe H
They are quarter elliptical spring setup. There is a spring eye inside the frame bracket that mounts one end of the spring with the shackle on the other end.

I built all the spring setup myself, here is the link and construction. It will show how it works.

https://www.jalopyjournal.com/forum/threads/built-my-own-quarter-elliptical-springs.1115374/


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So the chassis just rests on the springs? What holds the spring and chassis together when you hit a big dip or hump in the road, the shocks?
Just asking, I have no experience with this.

 

I would think that gusseting between the side of the frame. & The top of the spring " pocket" would be in order ?

 

@2OLD2FAST you are correct! I will actually gusset from spring pocket to either side of frame or to upper crossmember. I'm building a trans mount right now, once that's done the frame will be blown apart and all the welding will be finished, gussets and supports will be added and welded in. Right now most of the tube xmembers, battery box brackets etc are just tacked in. Easier to weld if I can flip the frame over to do the complete welds.

Also note that you can't really see it in the pics the frame bracket spring bolt is also in line with the lower 4 bar front bolt also.

@Joe H rhe easiet way I know how to explain it. Imagine that the spring is full length, now mount one end to a solid bracket on the frame, now you can just pivot the spring up and down but now Imagine that where the center bolt is we mount a bracket so the center can't move up and down.

Now we have the spring captured both in the middle and on one end. This makes the other end our flexible part of the spring or the weight bearing end. Basically that's what I did BUT the I shortened the static or the captured end of the spring, the new "middle" of the spring is being held by the end of the bracket and will rest against the big bolt that screws down thru the bracket which will allow me to adjust ride height just by screwing the bolt up or down.

Hope that makes since !

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Tensile stress and shear stress are calculated identically. There might be conventional adjustments due to the extraneous factors I mentioned e.g. stress risers at sharp edges etc.

 

[/Quoting Thought shear was about 60% of tensile ??

This should be interesting.

 

@lostone , you have not outlined exactly why you want to do this setup. I am genuinely interested in the reasoning.

 

Thanks for the explanation, hope it all works out for you.

 

@twenty8 , several reasons, 1- the Heiman would be a smaller foot print around the axle, giving me more room and clearance.
2- it would be a small pivot on the top of the shackle vs a wide 3" bolt/shackle setup. Think of it as the shackle being an "H" right now and trying the pivot that "H", now with a Heim joint my "H" becomes a triangle, with the Heim being at the top of that triangle. Easier, smoother pivot and flex. And I hope a better ride and I'm always up for thinking outside the box just to see how it works !

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You know, you've got a point. I missed that the nut puts the heim in tension, reducing the shear capacity by that amount.

If a bolt etc. isn't carrying any tensile stress, its shear strength is equal to its tensile strength. If a bolt is torqued to a given tensile stress, its tensile capacity, and therefore its shear capacity, is reduced accordingly. But we're not torquing the nut to any significant proportion of the heim's tensile strength; we're just tightening it down to keep the heim from moving. I don't think much shear strength would be lost.

(Of course in the classic structural bolt fixing's case we're relying on clamping force increasing the friction between different components, so that actual shear never even becomes an issue. That also needs to be considered, but it probably isn't a factor here.)

I still say that the likely failure mode here isn't going to be a shear failure between the nut and the rearend, but the heim bending on the ball side of the nut. If that happens repeatedly the heim would give way through fatigue. It'd probably hold up a while before that happens, so a bent heim would be a useful warning, but if the heim is going to bend it'll likely bend right away.

All this becomes moot with the solutions suggested by @Kerrynzl and @gimpyshotrods: simpler, cleaner, and entirely as compact as the OP's proposal.

 

Here is something to think about; As the suspension goes through it's travel the spring eye at the shackle end will change position as the spring flattens out (gets longer or shorter) and/or travels in an arc. This will produce a side load (shear) on the rod end shank with the nut welded in the vertical position even with the shackle. Even if the shackle is vertical at static ride height it's not going to stay that way during travel. The rear axle controlled by the 4 link may also rotate and/or travel in its own arc either further side loading the rod end shank or possibly cancel out some of the load produced by the spring eye movement. Will the pivoting shackle accommodate this with no side load on the rod end shank?

 

@tomcat11 @Ned Ludd these are things I have pondered, over and over.

But I always come back to the thought of the many many cars have been built with leaf springs and they have shackles with bolts 7/16 and smaller. Even the old cars with shorter springs and small 5/16 shackle bolts in them and survived for over half a century and many of them old ones did it on roads much worse than my car will ever see.

Those small bolts held up fine, now I don't claim to understand the dynamics or mechanics behind bolt vs size vs shear etc, just good Ole fashioned brain strain and trying to determine what works by previous cars before me.

Another thing I ponder, how many cars have been driven daily with ladder bar system under them. Now I understand I'm looking at using a smaller heim but I'm not putting this heim joint thru as much stress, side load, twist etc that the heim joint on a ladder bar will ever see.

Again no college degree just trying to sort thru the things I've seen done, things I've seen worked and didn't work.

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@lostone I think the difference is with a traditional leaf spring, the spring eye has large bushings with steel sleeves distributing the load across the entire shank of the bolt (7/16") while the rubber bushings dampen a lot of the shock. It is configured in double shear and the mount on the frame or subframe is usually quite substantial. Not sure what car would have 5/16" shackle bolts. The spring is absorbing most of the axle rotational force.

With your configuration the forces from the spring and axle will be focused onto a very small cross section of the 7/16" shank and only in single shear.

The minimum rod end shank diameter for a ladder bar is probably 3/4". I have seen some with 1" shanks. With materials being the same, the difference in strength between a 7/16" shank and a 3/4" shank is massive!

 

It's fun to note how misleading terms like daily driver can be ; the wife & I have a DD , it's a 2009 with 37K miles on it , obviously that's not many mikes for a DD . Our T got on the road in 2002 , it's far from what could be termed a DD yet it has 51K miles on it & hasn't been driven for 3 years .
With that said , the T has a ladder bar/ watts link / coil over rear suspension that works fine & hasn't exhibited any problems @ MY DD mileage .
As for spherical rod end strength , first year on the road , I bumped a " road hazard" with a front tire , 1/2" joint shank bent at the begining of the threaded portion of the shank ,bent about 3o* , after removal I put it in the vice & with a pry bar through the eye , snapped the head off....they arent very strong in shear OR I got a defective one .

 

Never let it be said that I am incapable of admitting that I was wrong. I owe @2OLD2FAST an apology.

I was confusing stress and strength. I think it was because my background is in heavy masonry structures, where shear is generally due to distributed loads on one side of a void (i.e. more chisel and less scissors) and materials don't have much by way of plastic ranges.

For the sorts of situations we encounter, shear strength is indeed derived from tensile strength via a factor of adjustment, which varies according to the material. In terms of stress yield strength to tensile yield strength, @2OLD2FAST's factor of 0.6 seems to be spot-on.

Mea culpa. I stand corrected.

(But I still think a bending failure is more likely here.)

 

I will say it again, just put a little long spring in with a slider under the axle. No need for any type of shackle or joint. The spring will rest on the slider and the slider will move forwards and backwards as needed without any stress or concerns.

 

@Joe H I thought about exactly that when I first started laying out the spring system.

I considered it but turned away for 2 reasons, 1- I thought the 2 springs were too close together and 2- I figured it would be a rougher ride due to the fact of no bushings to help absorb the bumps BUT now I'm lower the number of bushings anyway if I go to an upper heim joint anyway..

Still haven't decided anything yet, but it's one of those decisions I'm going to have to make soon...

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