Technical Question concerning heim joints *x2couple pics*

Setting up my rear leaf springs in my model A Tudor and I want to use heim joints but a little nervous even after reading the specs. First a little back ground.

I built my own model A frame, then I put a ford 9" with triangulated 4 link. Then I built my own semi elliptical leaf spring system. Now the 4 link takes all the abuse under both braking and acceleration, the springs only hold the car up.

So on to the set up, I have the spring shackle from the spring eye up to a bracket on the 9" housing as the other pivot end of the spring is bolted into the frame bracket that's welded solid.

Now my delimia, I want to mount the bottom of the shackle to the spring eye bushing (stock configuration) BUT I'd like to mount a heim joint to the housing and have to top of the shackle mount thru it.

Sounds doable... but 1 thing I'm trying to keep the upper shackle mount as small as possible. So after going thru QA1 catalog and looking at their chrome moly PCYMR7T heim joint, I like its size, 7/16" shaft and mounting hole. And it says it's good to over 17,000 pounds, after getting them they look awful small and got me nervous.

Now I figure the car to weight around 3000 pounds and when I figure that with 2 rear springs and 2 heim joints with a combined strength of over 34,000 my weight and usage shouldn't be an issue.

So my question is, am I really that safe with the weight to strength ratio? Am I over thinking this ? Or am I missing something ?

Thanks guys, I'm to that point where I have to figure this out to move on !!

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The shackles mount to heims, which are bolted to the rear housing? Sounds like you have too many parts. Weld some eyelets to the housing and slide the shackles through them.

 

I want to keep the upper mount as small as possible. With the "factory" style set up, I'll have as many parts as what I'm trying to do.

Heim vs factory style bushings I can loose at least 3/4" of width and almost 3/8" in diameter.

I'm concerned with weight and strength limits of the heim joints.

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Ok sorry, I just can’t picture it in my head. But good luck to you.

 

When I was building the rear suspension for my "Tub", I used Heim Joints. At that time, I found that Chrome-Moly joints are available that are rated at over twice the capacity of regular joints. I think I found them on a "Rock Crawler" site.

 

@alchemy no problem! I appreciate any responses.

I'll get some pics tomorrow, I don't have anything mocked up right now as I'm trying to figure out where I'm going here. I know my design is sound just want to make sure the parts are up to the job.

@tubman yes that's why I chose the chrome moly heims myself. I look at that 7/16" heim joint and think "how can it be that strong?"

But I guess I shouldn't be too surprised, the stock shackle bolts are 7/16" diameter and they are only grade 5.

Again maybe I'm just be too cautious...

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For strength you should be ok, but I do hear that the non serviceable Heims do get noisy (clicky on movement) after awhile as they loose the Teflon insert.

 

I have trouble visualizing your setup, but I don't think using 17k heims allows you a load of 34k.
EACH is still 17k. At 17k, they both fail.

 

I'd like to to see a picture or sketch to visualize your setup before making any suggestions.

 

On a technical point the rear shackles on a transverse leaf set up take substantialy more than the weight of the car because they are operating at a shallow angle. This multiples the load on the shackle bushes. On a high arch spring its even greater.

 

THIS

 

I realize you haven't yet posted a picture of your intended suspension design but I think I may understand why your rear suspension is so hard to visualize. At first I didn't understand why you would want or need a four-link when running parallel leaf springs (semi-elliptic) or why you would intend to mount a shackle to your rear end housing until it hit me ... I think you mistakenly said semi-elliptic when you actually mean quarter-elliptic. Instead of mounting the leaf springs solidly to the housing and the frame like pictured below, you are intending to mount a shackle system to the rear housing, allowing it to "float" while the four-link does the job of locating the housing. Again, just guessing here.

My other guess is you actually are running a four-link and true parallel leaf springs (semi-elliptic) and you are trying to design a "housing floater" similar to those used by drag cars that run both leaf springs and ladder bars or four-links. Again, just guessing with this one too. The bottom pic is a housing floater.

Knowing that Model A Ford don't have a lot of/any frame behind the rear end, I doubt you are running true semi-elliptical leaf parallel leaf springs and if you were, you wouldn't need any other type of locating device or any sort of shackle system on the housing but since this frame is homemade and your suspension is of your own design, without some clarification or pictures, it's kind of impossible for anyone to fully understand exactly what it is you are attempting here

 

My thought would be that even though the car weighs nowhere near 17,000 pounds I would assume that the shock load from hitting a bridge expansion joint or big ass pot hole at speed would be a lot higher than you expect.

If you’re so tight for room that you need a 1/4 of an inch just move your ladder bar/ four link mounts over a bit.

 

I have no ties to this company. However, while building my cars have found their catalog very useful and have purchased numerous items from them. They have a good selection of spherical bearings (Heim Joints) in various materials, sizes, race materials, etc to fit builders needs. https://midwestcontrol.com/shop/

 

@borntoloze you are correct, quarter elliptical, my auto correct and I didn't catch it.

I will get a sketch up later today!

Guys thank you !!

 

Here is a pic I found od my set up.

I'm wanting to remove the upper shackle mount on rear-end with the heim.

I'll remove the tube on the upper bracket and weld in a nut facing front to back and have the heim screw into that. So the heim will also be running front to back. Then the upper shackle will taper from spring eye to heim joint.

I will get a better pic of what I want to do but bot home now, but this pic will give a better idea..

 

Very interesting setup. Still not clear on what you are trying to accomplish, but looking forward to understanding as I will be using 1/4 ellipticals (front & rear) on my speedster build, and I’m not sure of the original geometry the builder of car I’m copying used for the rear. Some pics for comparison purposes.

 

Not sure where you'll end up, but do agree that needs to be changed.
I just think at best it is a rough ride.
But where are we gonna go? The movment needs to respect an arc.

 

I am assuming that you want to get some bind out of the current setup. As currently built it's more complicated than needed, and you have a lot of competing movement arcs. Many set ups use the quarter-elliptic springs as the lower bars for the triangulated 4-link. With soft bushings they seem to work fairly well.

 

If I’ve read it right I’d suggest you don’t want the link to attach to chassis and spring end of the shackle as that’ll bind up the spring.

If I’ve read it wrong and you’re just asking about using a Rose joint to connect spring to axle then we do that on OT race cars so if you use the right joint it’s been done before.

 

You need a johnny joint.

 

OK I got a couple more pics to look at.

From pics above you can see the set up.

Next pic is of just the upper shackle mount on rear axle. Second pic is what I am aiming to do.

I will cut just the upper rubber mount tube off of the bracket, leaving the entire bracket. At which point I would take the coupling nut and integrate it into the existing bracket and screw the heim into that.

As far as geometry I have no problems with binding. With the springs un hooked I can articulate the rear housing 4 or 5" by hand up and down side to side with no problem.

I don't have the strength to do it with shackles connected ,haha ! But when I had the car basically together standing on the rear or standing in either door opening and rocking the car I never had any feeling of a problem with binding, infact it felt really good. I was surprised how soft and smooth the suspension felt.

I know the design will work, it's the strength of the heim joint.

 

Use a Safety Factor of 10x on suspension components.

 

Have you looked at Johnny Joints?

 

Are you referring to mounting a heim to a common bolt like the Shackle Bolt.
This "common bolt" practice is often used on Race cars where the "through bolt" had a clevis head



Top view

 

50k miles over 23 years & none of my spherical rod ends are " clicky" or worn or loose or malfunctioning .

 

@Kerrynzl something like that BUT the clevis will actually be the shackle itself. The threaded end of the heim will screw into the housing bracket.

@redo32 , @X-cpe yes I have looked at Johnny joints, but if I can do the same thing with a heim joint because it's smaller and cheaper. This joint will only be holding the weight of the rear of the car. No braking or acceleration forces of any kind against it.

The heim will screwed into rear housing bracket, shackle will go on each side of heim and shackle bolt will go thru heim eye.

I'm just wondering IF According to their specs a 7/16 chrome moly heim is strong enough to hold the weight of the car and support the spring pressure.

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Here is another picture, this is the way the Heim joint will mount to the spring by way of the shackle. EXCEPT I will taper the top of the shackles to match the width of the heim.

 

I say nope, but don’t have any data to back it up.

 

Yeh, what could possibly happen?
Me thinks the cheapest route would be to spend more money!