Suspension Bind

[TriodeLuvr]

You can see by the photo, I would have to really chop up the body to clearance them...

Mine is also channeled, but the front heim is attached to a bracket under the frame. To clear the body, the top rod is straight. Maybe yours is too low to the ground to use a bracket under the frame. Hard to tell from the photo.

Jack

 

[bobs66440]

It looks like your misalignment spacers are installed backwards. The small end should be at the heim end.

Those aren't misalignment spacers. That's the ball in the rod end. The only spacers I have are the two washers on either side of the rod end.

 

[bobs66440]

Couple things I see.

1 - you may need some "misalignment" spacers on the front mount, that will allow that heim to twist a lot more. If you disconnect the rear bolts, and twist that joint, you will probably see its hitting very early in the rotation.

2 - those hiems bolted like that on the rear probably only move side to side, which is what the panhard bar will prevent,so they probably won't be any different then the clevises. They do sell clevises with 1/2 holes, they just cost a bunch more, I picked up one up at speedway, for $19!

http://www.speedwaymotors.com/AFCO-10491-Steel-Clevis-5-8-18-RH-Male-1-2-Hole-3-8-Slot,23917.html

Those rodends, might be another option to give you a bit of movement in the rear. Though you will get the single sheer argument again.


Oh yeah, that front mount will make a great spot for a step!

1- I agree about the front mount, but when I was building it I made sure it had plenty of movement available for what it's doing. During the design/build process I have cycled the suspension through it's full range of travel many times. The way I have it designed, the front rod can only twist about 15 degrees in either direction, but in reality as it goes through the full travel with coilovers disconnected, it only turns maybe 5 degrees. And with everything connected, at ride level and loaded (because it doesn't articulate much due to the bind, and the suspension travel is only maybe 2-3 inches anyway because it's such a light car with relatively stiff suspension) it probably only moves 1-2 degrees.

2- I'm not sure what you mean about the side to side thing. The heims don't move side to side or restrict side to side movement of the axle. But I'll check out those clevises. They definitely look better than the heims.

Using that mount as a step mount was in the design plan all along. But after I had the car all together, I rigged up a step to test and it turned out that the body is low enough that it was actually easier and less awkward to just step in over the side, lol.

 

[bobs66440]

1 - you may need some "misalignment" spacers on the front mount, that will allow that heim to twist a lot more. If you disconnect the rear bolts, and twist that joint, you will probably see its hitting very early in the rotation.

Even at this extreme angle (which it would never reach) the heims do not bind.



BTW, this is with just one bolt disconnected from one rear radius rod. Totally frees it up. It makes me think about a 3-bar design for the rear...hmmm.

 

[bobs66440]

Mine is also channeled, but the front heim is attached to a bracket under the frame. To clear the body, the top rod is straight. Maybe yours is too low to the ground to use a bracket under the frame. Hard to tell from the photo.

Jack

Yes, I had those same brackets but I would have had to extend them down 2" more to clear the body. Mine is channeled the same as yours, but the kick up in the frame is 2'' longer to lower the car, so that's the difference.

 

[bobs66440]

I've always heard that these cars have limited suspension travel. I wonder if the limited travel is due to the hairpins and tube axles more than anything else.

I have 4 bars on both ends of my car and it has plenty of travel. I can drive over curbs and speed bumps at an angle with no trouble.

Really not trying to "stir the pot", just wondering.

No worries. There's no doubt, the 4-bar is a superior design.

 

[Mike J]

Even at this extreme angle (which it would never reach) the heims do not bind.



BTW, this is with just one bolt disconnected from one rear radius rod. Totally frees it up. It makes me think about a 3-bar design for the rear...hmmm.

Wouldn't you still need 4 bars (links) 2 bottom and 1 pan hard and 1 for stopping rear end twist? Just thinking out loud

 

[Keeper]

Cool, looks like you have plenty of movement without any spacers. If you have your bucket twisted that far, you have other things to worry about....lol

To clarify the heim comment, with the two of them bolted on the axle they way they are, they cannot twist at all, only allow the axle to move side to side. Not an issue, just an observation.

 

[Hackerbilt]

You flipped my lid with all that rear twist...until I read you had one bolt removed!!! Holy crap!!! Hahaha

One thing about using a hairpin or ladder bar only on one side...I have READ (no real world experience) on both 4x4 vehicle and Hot Rod sites, that doing that can lead to unusual handling, acceleration and braking, due to only one side of the axle applying rotational torque into the chassis. Basicly the car can torque steer in braking and in acceleration.

NOW...I've read that in a couple of very different locations and it seems to make sense...but as I said, I have NO real world experience to say if its true or not.
Just mentioning it to create discussion about the potential.

 

[fluidfloyd]

Even at this extreme angle (which it would never reach) the heims do not bind.



BTW, this is with just one bolt disconnected from one rear radius rod. Totally frees it up. It makes me think about a 3-bar design for the rear...hmmm.

Bob,

Just a few points I would like to make about ladder bar/radius rod/ hairpin types of suspension. The first point is that everyone of those designs needs to be thought of as an anti roll bar. The housing is the tube and the radius rods are the arms. It is considered to be a one piece rigid assembly with the housing doing the twisting as loads applied to the arms. If you will look at your suspension from the rear view you can see that the hairpins are no longer in the same plain. The front pivot points are at different heights while the rear axle center line is about the same height right to left. This has to be caused by something either bending (hairpins) or twisting (rear housing). The frame appears to be stiff in the torsional axis as it should be. That is why Henry Ford angled the radius rods an intersecting angle and let everything roll at that point without any bind. The design you and many others have can cause unwanted and excessive torsional stresses on the axle housings. The worst housings to use in this design are the iron center section with press in steel tubes. These housings are usually just plug welded 3-4 places to hold each tube in. High driveline torque and sticky tires can and do spin the tubes in these type of housings. The shorter the radius rod the high housing stress.

As to the arm designs... The Ford OEM radius rods are at the best 66 years old. A lot of years to take on internal corrosion or rust. Minimal grade steels of the day and questionable cross sectional shape and strength depending of the applied power. Hairpins are probably a better choice just due to age. However I do think that under extreme loading they might well be "S" bowing to some degree. As long as you don't exceed the yield strength of either the arm or the housing everything will return to it's original position as the load decreases.

For these and other reasons I prefer a fully articulating system of some kink. A 4 bar is not bad. A triangulated 4 bar is even better but can be tough to package in some types of T- buckets. As in any of the above mentioned systems with the exception of the triangulated 4 bar you will need to run some type of centering devise such as a panard bar or a watts linkage. One other thought...If you build up a hairpin system that is stiff enough to resist any twisting or bending then I believe you will start seeing chassis twist. These types of cars are usually just parallel frame rails and several cross tubes with little or no X or K members. They also have very little vertical section to help resist that twisting effect. I firmly belief you need a very rigid and stiff frame and a fully articulated suspension. I realize these are not road racing cars but the public streets and highways are not always a smooth surface. Littered with pot holes, surface patches, dips and bumps they can and do cause your suspension to work pretty hard.

I hope this has been of some help to you and others. I am about to under take a very similar problem in a vintage sports car project. This will be a long term project but at some point the customers will let me talk about it. I will keep you posted when that time come. Take care and good luck.

George

 

[GAB]

This pic is of a 4 bar front and rear with all of the springing hooked up. There is little attempt to twist the frame since each wheel is free to move in a vertical direction independent of the other one on that axle.



O.K. you say that you would like to free the suspension up but just can't live without the hairpins looks. Try this for an idea for creating a 3 bar.



Anyone figure out what this is all about?

 

[bobs66440]

Anyone figure out what this is all about?

Yes, I thought about having some type of slider or even like a shock absorber/spring setup on one bar to allow it to free up. But it could get really complicated, and as mentioned, it's probably not that critical considering the small amount of suspension travel we have.

Wouldn't you still need 4 bars (links) 2 bottom and 1 pan hard and 1 for stopping rear end twist? Just thinking out loud

I think that's what Hackerbilt is referring to and I agree.

You flipped my lid with all that rear twist...until I read you had one bolt removed!!! Holy crap!!! Hahaha

One thing about using a hairpin or ladder bar only on one side...I have READ (no real world experience) on both 4x4 vehicle and Hot Rod sites, that doing that can lead to unusual handling, acceleration and braking, due to only one side of the axle applying rotational torque into the chassis. Basicly the car can torque steer in braking and in acceleration.

NOW...I've read that in a couple of very different locations and it seems to make sense...but as I said, I have NO real world experience to say if its true or not.
Just mentioning it to create discussion about the potential.

I don't have any experience either, but it sounds about right. A friend of mine mentioned maybe having one rod on each side on the bottom and one on the top of the differential going straight forward to a crossmember. That would make it super easy to adjust pinion angle. And it would be symmetrical and you could use a normal panhard bar like I have now. That seems like it would work...Or even two bars going from the top of the diff triangulated out in a vee shape to the frame. I've seen that before.

 

[bobs66440]

Bob,

Just a few points I would like to make about ladder bar/radius rod/ hairpin types of suspension. The first point is that everyone of those designs needs to be thought of as an anti roll bar. The housing is the tube and the radius rods are the arms. It is considered to be a one piece rigid assembly with the housing doing the twisting as loads applied to the arms. If you will look at your suspension from the rear view you can see that the hairpins are no longer in the same plain. The front pivot points are at different heights while the rear axle center line is about the same height right to left. This has to be caused by something either bending (hairpins) or twisting (rear housing). The frame appears to be stiff in the torsional axis as it should be. That is why Henry Ford angled the radius rods an intersecting angle and let everything roll at that point without any bind. The design you and many others have can cause unwanted and excessive torsional stresses on the axle housings. The worst housings to use in this design are the iron center section with press in steel tubes. These housings are usually just plug welded 3-4 places to hold each tube in. High driveline torque and sticky tires can and do spin the tubes in these type of housings. The shorter the radius rod the high housing stress.

As to the arm designs... The Ford OEM radius rods are at the best 66 years old. A lot of years to take on internal corrosion or rust. Minimal grade steels of the day and questionable cross sectional shape and strength depending of the applied power. Hairpins are probably a better choice just due to age. However I do think that under extreme loading they might well be "S" bowing to some degree. As long as you don't exceed the yield strength of either the arm or the housing everything will return to it's original position as the load decreases.

For these and other reasons I prefer a fully articulating system of some kink. A 4 bar is not bad. A triangulated 4 bar is even better but can be tough to package in some types of T- buckets. As in any of the above mentioned systems with the exception of the triangulated 4 bar you will need to run some type of centering devise such as a panard bar or a watts linkage. One other thought...If you build up a hairpin system that is stiff enough to resist any twisting or bending then I believe you will start seeing chassis twist. These types of cars are usually just parallel frame rails and several cross tubes with little or no X or K members. They also have very little vertical section to help resist that twisting effect. I firmly belief you need a very rigid and stiff frame and a fully articulated suspension. I realize these are not road racing cars but the public streets and highways are not always a smooth surface. Littered with pot holes, surface patches, dips and bumps they can and do cause your suspension to work pretty hard.

I hope this has been of some help to you and others. I am about to under take a very similar problem in a vintage sports car project. This will be a long term project but at some point the customers will let me talk about it. I will keep you posted when that time come. Take care and good luck.

George

Thanks for the detailed info! I'm still learning and I enjoy learning about the science and physics behind all these designs. I used to race dirt karts, road race karts, SCCA, etc. and we would stay up all night brainstorming the next new revolutionary breakthrough design for everything, ha ha! Of course, we didn't know that everything had already been thought of at some point, but it was fun anyway, lol!

 

[TriodeLuvr]

I'm just going to throw one fly in this ointment... If in fact the radius rods under discussion do - in practice - act as sway bars, conversion to four-bar or its equivalent at all four corners of the vehicle will result in increased body roll. Body roll is generally detrimental to handling in corners, and it's not the direction I would personally want to go with this type of vehicle. I suspect it would take quite a bit of suspension tuning and customization - probably including softer springs and actual sway bars - to achieve better real-world handling and "driveability" from a four-bar system.

Jack

 

[bobs66440]

I think fluidfloyd is 100% correct, but there are varying degrees of the actual mechanics of it depending on the design. He says that the housing is the tube and the radius rods are the arms of the "anti roll bar" and that the housing does the twisting. In my case, or in the case of cars running relatively flimsy radius rods, I don't think the axle is twisting much if at all. I think the radius rods are flexing. Now, if you are running super rigid triangulated or heavily gusseted radius rods or ladder bars, then I believe the axle will twist or the frame will flex as he said, or a combination of all of the above.

Regarding body roll, I think because these cars are so light, you wouldn't see much more body roll with a 4-bar. There just isn't that much mass to overcome the front and rear springs that most guys use. But a 4-bar would allow you to fine tune the ride as you mention. I haven't driven mine yet (I have 140lb springs in the rear), but I read a lot of complaints about a stiff ride. A sway bar would allow you to use a softer spring for ride quality, but maintain handling. Best of both worlds.

Installing a sway bar wouldn't be too difficult. You could get away with one just in the rear.

 

[TriodeLuvr]

I think fluidfloyd is 100% correct, but there are varying degrees of the actual mechanics of it depending on the design. He says that the housing is the tube and the radius rods are the arms of the "anti roll bar" and that the housing does the twisting. In my case, or in the case of cars running relatively flimsy radius rods, I don't think the axle is twisting much if at all. I think the radius rods are flexing.

It's my opinion also that the radius rods in these cars are much too flexible per unit of length to act as sway bars.

Now, if you are running super rigid triangulated or heavily gusseted radius rods or ladder bars, then I believe the axle will twist or the frame will flex as he said, or a combination of all of the above.

If the radius rods are really so stiff that there's little or no flex, I believe the combination of bars and axle will act as if both wheels are tied together. IOW, when one wheel is pushed up by a bump in the road, the other wheel will move up as well (exactly what would happen with a very stiff sway bar). I have no small difficulty with the concept that the rear axle will twist before that happens, especially given the minimal amount of weight in the rear of these vehicles.

Regarding body roll, I think because these cars are so light, you wouldn't see much more body roll with a 4-bar. There just isn't that much mass to overcome the front and rear springs that most guys use. But a 4-bar would allow you to fine tune the ride as you mention. I haven't driven mine yet (I have 140lb springs in the rear), but I read a lot of complaints about a stiff ride.

I agree, and this is why I don't think there's any significant benefit to the four-bar. Springs and shocks simply don't offer the compliance that would be required in order to use a more independent suspension with greater travel capability.

A sway bar would allow you to use a softer spring for ride quality, but maintain handling. Best of both worlds.

Installing a sway bar wouldn't be too difficult. You could get away with one just in the rear.

THAT would be an interesting ride. Four-bar still might not provide significant benefit though, depending on how stiff the sway bars are. A stiff sway bar won't allow the type of "differential" movement between same-end wheels that takes advantage of the four-bar design. It only allows untensioned travel when the wheels are moving up and down simultaneously, and for that, radius rods work just as well. The only exception I can think of to that would be a situation in which the springs are so soft and and "simultaneous" suspension travel so great that radius rods would cause a significant change in pinion angle.

Jack

 

[fluidfloyd]

Thanks for the detailed info! I'm still learning and I enjoy learning about the science and physics behind all these designs. I used to race dirt karts, road race karts, SCCA, etc. and we would stay up all night brainstorming the next new revolutionary breakthrough design for everything, ha ha! Of course, we didn't know that everything had already been thought of at some point, but it was fun anyway, lol!

My Pleasure Sir!

 

[fluidfloyd]

It's my opinion also that the radius rods in these cars are much too flexible per unit of length to act as sway bars.

Jack,

I tend to believe you're correct. Just by the fact that the housing tube is around 3.0" in diameter means you a have a very stiff section. Not having a car here I have assumed some numbers and calculated the rate on such a suspension. This was also assuming the 3.0" tube ran straight through and did not factor in the differential cross sectional area change.

48" long x 3.0 OD x .188 wall tube.
36" long radius rods that are 48" apart.
This gives us a torsion bar rated at 702 in lbs.

I to think you would bend or flex radius rods depending on their tube size, parallel or verticl spacing and any spreader/stiffener tubes or gussets.

If the radius rods are really so stiff that there's little or no flex, I believe the combination of bars and axle will act as if both wheels are tied together. IOW, when one wheel is pushed up by a bump in the road, the other wheel will move up as well (exactly what would happen with a very stiff sway bar). I have no small difficulty with the concept that the rear axle will twist before that happens, especially given the minimal amount of weight in the rear of these vehicles.

I agree, and this is why I don't think there's any significant benefit to the four-bar. Springs and shocks simply don't offer the compliance that would be required in order to use a more independent suspension with greater travel capability.

I agree with you as to the wheels/rear housing trying to stay together as it moves up and down. However I do think it will twist under hard leaning or turning loads. When one wheel hits a pot hole or a road bump I think the sudden impact loads can be off the chart. I think that the chassis absorb a lot of those sudden loads by deflecting or flexing. There's not much tubing in these cars to resist these types of forces. Everything is a trade off. I've thought about this for a number of years and still haven't made a final decision as to what I want to do. One thing I do know, Diameter and Double Shear are my friends.

THAT would be an interesting ride. Four-bar still might not provide significant benefit though, depending on how stiff the sway bars are. A stiff sway bar won't allow the type of "differential" movement between same-end wheels that takes advantage of the four-bar design. It only allows untensioned travel when the wheels are moving up and down simultaneously, and for that, radius rods work just as well. The only exception I can think of to that would be a situation in which the springs are so soft and and "simultaneous" suspension travel so great that radius rods would cause a significant change in pinion angle.

I wouldn't even run an anti roll bar in on either end of these cars. I just don't think they are necessary in such light cats. If I was running an engine that Screaming built then I would probably reverse that decision. The front axle/radius rods would be the anti-roll system. If needed I would then add a rear system too.

George

Jack