Death Wobble - speedway tie rod may be suspect

I think the tierod is gonna flex a bit just due to the length compared to the thickness...especially in use as it hits bumps etc.
The steering arms are thin and will also flex a bit due to the Heims being mounted in single shear off the top or bottom of the steering arm. Might be worse again with a normal tierod end. Arm flex alone would account for some toe change as the wheels are pushed/pulled.

Millions of these setups (factory and aftermarket) have been in use over the years and only a small percentage have major issues.
I think its just the combo of parts you have.
Like mixing and matching engine components to put tolerances where you want them (even though all parts are supposedly the same)...your steering combo just happens to fall to the side where flex and natural stiffness is just poor enough to allow a little extra flex and the resulting death wobble.

I don't think theres much magic involved...if you get it you deal with it as required and move on...

Hambandys car runs a Speedway setup and works perfectly. We just bolted it on!

 

The flex is more fore to aft than up and down. That is why you can't see much of the movement from the video taken in front of the car.

 

I think the detailed stuff that Dick posted a few posts back explains it. I'm an engineer myself and we sometimes think the root cause is the one thing. I have found that most of the times it a combination of several as others have said. I bet $100 if I took my 32 truck which does not death wobble and slapped on a conduit piece for a tie rod, it would not wobble. Its not the one thing.

 

The post that never stops, to get so many looks you'd think there was an offer for free beer. Ok I took some more shots to go with Dog Patches Utube link. Yes you can see that the rod does flex. Lets examine what is happening in real time.

First the only way that you are going to have a force applied to the tires that generates an outward force is when you run in a state of toe out or again if you have an excessive caster angle creating a long trailing moment. Under most conditions the tires run down the road in a state of equilibrium and the resistance to each is balanced. If you have an unequal caster this will change the balance.

Since an I beam axle is a positive camber axle you don't run toe out, this exaggerated rotation scuffs the tire tread off on turns. So this gets us back to the geometry of the steering arms and the spindles.

Now CoolHand has brought up the angle that the tie rod end bolt addresses the steering arms and that is a valid point as this determines the angle of force applied on the rod. If you check the picture of the stock spindle you will notice that the end of the steering arm is machined and twisted to a slight angle corresponding with the king pin CL. This is similar to the CE steering arms in the later picture.

Now as the force applied to the tires by hitting a severe bump would be magnified by the angle of intersection with the bump and the caster angle. However the force would probably be absorbed more in the tires and dissipated. As long as the wheels where rolling straight ahead the caster would not be totally effected. On a turn however the bumped wheel would be forced right or left and in most cases force the corresponding wheel to rotate in conjunction with the bumped wheel and this would be felt in a jerk of the steering wheel, This would be termed bump steer and not the same.

Could this external force hitting both tires at the same time bend the tie rod , yes but the force would be excessive to the rod material construction and you would probably broken something else also. The original question is why does the tie rod bend under compression? It does because the force applied to it is not applied directly thru the center of the rod. The angle of the steering arms and the relation to the applied forces are a different angles and the tie rod bows to compensate for the off center forces. You could run a piece of electrical conduit for a tie rod if you balance the forces to act thru the center of the rod. In this instance the tie rods bow because the arms are applying a force off center of the tie rod as I stated before, not because the tube is too weak.

One thing I noticed in playing with a bunch of steering arms is that there may be a degree of difference in design between manufacturers parts. In the other corresponding pictures tests I made using Chassis Engineering steering arms seemed to have the tie rod bolt hole position at an angle so it rotated in an arc to maintain the ackerman angle as the steering arms rotated.

So now 12 pages later "Does Tudors tie rod bow under compression?" Yes. He not nuts.

Is the rod junk ? No,

What can be done, easy just change the angle that the external force applies to the tie rod thru the steering arms so that it goes thru the centerline of the tie rod..

In all the following pictures the axle is set at 11* king pin inclination and 7* caster.

 

Awesome! Well said.

 

so what is the proper way to set up the steering arms to get the through center of the tie rod., if you need to bend them, do they need to be the sam angle as the caster....

 

I was wondering about this myself, since the pivot points are still on center, whether it be a Heim or standard tie rod end. Also, even if there is some arc in the steering arm through its range of motion, and there was some amount of friction in the ends, it wouldn't seem to be all that relevant anyways, being that the arms are stationary when the problems occur.

 

Yeah, I think Dick was confused about which pieces I was talking about being misaligned.

You are right, that a heim or a tie rod end will "find center" and align the force with the long axis of the tube, provided that the end of the tube was tapped square to begin with.

It's like this:



That offset causes a bending moment in the tube, whether it is loaded in tension or compression (though the effect is most easily seen in compression).

I do not believe that the changing arm angles will have any effect on a self centering joint like a heim or tie rod end.

 

Nice graphic.

 

Thank you.

Have AutoCAD, will travel.

 

Please let me know what works I have same problem.

 

did you miss the preceding THIRTEEN pages....

 

I just redid the spindle bushings and kingpins on my gasser project, mine were pretty well worn and there was a lot of movement everywhere! Yeah, the drag link, tie rod, wheels, all moved around a lot before I installed new bushings in the spindles and reamed them to fit properly with the new kingpins. There is no movement at all now that I can see, and the tie rod and the new Speedway drag link have no flex in them at all that I can see. It seems like an accumulation of slight looseness in the kingpins, slight flex in the steering arms, slight looseness in the heims or ball joints, and the tie rod can move around quite a bit when pushing on the tires.
2L.

 

Damn good read.

 

Flathead 31, You better start a new link for this question. Now to start a firestorm, bending your steering arms is the start of problems. This is just another one of these "well they did it like that in the old days, it should work today philosophy". Didn't work correctly then, doesn't work correctly today. We are very lucky today that there are a number of companies that make good bolt on steering arms to overcome construction faults.

The question is can you bend the steering arms, Yes, but as soon as you bend the steering arms you are changing the geometry of the spindle steer. By lengthening or shortening the steering arm you effectively change the ratio of rotation on the spindle to the length of the steering box arm. This slows up or speeds up the degrees of spindle rotation based upon the distance the newly bent steering arms travels in relation to the steering box rotation distance. Shortening the steering arm distance to the king pin speeds up the rotation and the reverse is true, lengthening the arm slows the rotation. This can make your ride steer erratic based upon your steering wheel input and the fact that one side arm may be bent at a distance or angle different than the other side arm. In addition bending the steering arms can change the Ackerman effect on the tires and the toe out on turns principle to incorrect degrees of rotation, under turning or over turning the wheels. If you want to continue on with this just clip and repost as a new question and it can go on from there. This post has gotten pretty big.

 

i see thanks, last ? can doing this with the steering arms cause the wheel wobble when you hit a little bump in the road? with all new front end parts, wobble has been there scence day one of the first drive.....

 

I was looking at some pictures of your car I'd say you need to ditch the cowl steering since it's positioning puts the drag link geometry out of whack. It will cause bump steer which could explain the wobble alone, not to mention the extended steering arm that is undoubtedly flexing and compounding things. I also looked deeper into your previous posts and noticed that a lot of these guys already pointed this out a year ago.

 

thats true.... and thanks for the advice, but their are a few guy on here with the same setup and the same angle on the drag link, that seem to have no problems, here is one, iam not posting on this thread again, its a long one, but if need be i will start a new one, thanks.....

 

The car in the picture sits quite a bit lower than yours and appears to have a less severe angle to the drag link. It also looks like the steering arm on the spindle is straight or close to it and would have little or no flex in it. Suspension travel in this case can play a part as well. At low speeds, when you hit a bump, the drag link is trying to move the wheels because of the opposing angles between the drag link and radius rod, which are moving in two different arcs. When this happens, your extended steering arm is most likely rebounding some and the resulting bounce could account for the low speed wobble, which may be lessened at higher speeds do to the centrifugal force of the tires trying to resist it.

 

it would bee cool to see who owns this car and get some insite on it,btw i to re read the past post on this and i think the anwsers have been covered, as well...

 

I never have bought into the relationship between the intersection angle of the drag link and the radius rod / wishbone/ hairpin theory. I have seen far to many examples runninng around that contradict the theory. If you look back to previous posts on this thread you'll find I wrote regarding this idea and I think someone else might have also. The short story I have concluded is, search out a copy of The Bear Alignment Guide for track roadsters. It offers more info then you probably would care to know about diagnosing and adjusting steering, ride height issues and weight bias in big cars, ie. Indy track roadster, The suspension and steering of some of the early models it covers, such as cars from the late 20's and early 30's era use much of the same components we are dealing with today. My copy was published in '39 and as I've said before these guys and their European couterparts were running well over 150 mph at times on roads made of bricks and cobble stone at best. They dealt with many of the same issues we have today and it was all that difficult for them to correct an ill handling car. Look to the past were all their practical experience has already figured it out for you.

 

I'm not sure I follow you. When all three pivot points: steering arm, Pitman and radius arm intersect (or at least the closer the drag link end of the Pitman arm and radius rod axis are together), they move in basically the same arc and this is the ideal configuration for this type of suspension. Things, however change a little with parallel leafs and four bars where the best setup is to have the drag link more parallel to the ground. If you deviate from this some and there is minimal suspension movement, the vehicle may not be all that unruly. Also, if you are suggesting that flathead31coupe's steering setup is kosher, you must not have checked it out yet.

 

Now there is a book I wouldn't mind reading. I had no idea Bear would have written something like that. Thanks for the info

 

hey now dont hurt me too bad it was my first build, and thats what i wanted, anyway i can drive it the way it is, and have. because i know what to look for, and i could get a stabilizer, but that thats not the anwser, so ..iam now going with a box under the frame, and a shorter drag link, thats Parallel, to the radius rod, and level with the steering arm. we will see....

 

Sorry, I just thought 777's comment seemed a little out of place.

 

no harm done

 

Hey guys I am having the same exact problem hence my reason for checking this post. At low speed only, when hitting a bump or whatever my front end begins to wobble and turns violent unless I come to a complete stop or power out of it. I have the exact speedway tie rod that measures 42" and it also flexes by grabbing both tires and pushing and pulling. All the components are new and consist of split wishbones, superbell axle, spring mounted behind the axle and friction shocks. I have played with changing the toe which only seems to make it worse, 1/8" in seems to work best. My next step is to change the tie rod to something more rigid. However, does anyone know if too much caster could cause the problem? And how about adding a steering damper?

 

Here we go again. Center link front or rear? Cross steer or front to rear? Pictures help a lot too.

 

777,
I'd like to have a copy of that Bear book, any idea where to get it?
Or could I pay you to make a photocopy of the one yo have and mail it to me?
I have no idea whether you're speaking of a pamphlet or a full fledged book.
But I'm serious in wanting a copy or whatever.
Dave

 

Coast57, yes, too much caster can cause it, see post 84 for a list of possibilities.