Death Wobble - speedway tie rod may be suspect

Not to muddy the waters on the issue, but if the stronger tie-rod doesn't fix it look into the pre-load on the king pins. The death wobble is a big problem with early Jeeps, and it was bad in my '48 CJ2A. Proper adjustment of the king pins fixed it. The procedure I was giving for setting up the king pins was to disconnect the tie rods and use a sping scale (like a fishing scale) to pull the spindle. For the Jeep axles you wanted to get close to 12 lbs of resistance before the spindle would turn. So it was an interative process of swapping shims till the resistance was right.

 

wow - they are supposed to be that stiff to turn???

 

it's behind...and I don't really want your blower..just get that bad boy fixed so you can go to the Redneck Rumble.

 

Tudor: 12 lbs was the number I was given by an old school Jeep guru. That was 12 lbs pulling from the steering arm where the outer tie rod will drop in. Not sure if that is 100% applicable to hot rods vs. a 4x4 axle, but could at least be a starting point. It worked in my case and the steering wasn't noticable harder to turn afterward.

 

To get a preload adjustment you need to have 2 opposing bearing surfaces that you can adjust tighter to each other. Some 4x4's have that due to needing to have the axle pass thru the area where a full kingpin would pass. Thus they OFTEN use an upper and lower king pin with a bearing on the upper and a bushing on the bottom. (Not all 4x4's use this system)

With an early Ford and the OEM slip fit, full length pin per side...how you gonna adjust it to add or subtract preload?

 

Ok here is my take on this. First of all there is no way you can bend a tie rod or bow it significantly enough using a 6" steering arm as a lever under compression by hand. I took a tie rod off the shelf to see how difficult it was and its not easy. You are looking at the wrong end of the horse. Are you sure that you are not just seeing this rise and fall as the king pin inclination rotation angle changes the steering arm position . I would also caution you against using heim ends for linkage connections , they are fine on race cars that have high maintenance and little mileage but on a street car even if they look goofy, a tie rod end is a better choice. Now if you are getting a severe shimmy at low speed it is usually due to excessive or unequal caster between front tires.

Now there are a number of other things to take into consideration but excessive caster creates a trail angle that continually wants to correct itself to maintain a straight ahead rolling motion. With excessive caster any deflection of the caster angle causes the spindle to rotate quickly back to straight ahead so fast that the spindle swings thru the centerline and initiates a caster trail action in the opposite spindle that wants to also return to center thus the excessive shimmy. Because both wheels want to return to center, they are fighting each other and the only way to rid this energy is to slow to a stop to loose the wobble in your case. With your car on the ground take a simple bubble gauge protractor from the hardware store and place it on top of the king pin flat and perpendicular to the axle ,write down the angle that you read. It should be between 4 and 7 degrees of inclination rearward and even on both sides. Any more than that creates problems you should favor to the lesser number. Because you say that you only run 10lbs air in skinny tires leads me to believe that this low air pressure is masking some alignment issue.

My next suggestion is similar to other posts, that being you have something else loose, in most cases that is the king pin bushings, jack the car up and grab the tire and rock the wheel and tire between the 12 and 6 oclock position, you should have a slight wiggle from the wheel bearing clearance but this should be minimum. You should pay close attention to the movement of the upper and lower spindle boss on the king pin . If this is sloppy this will also cause issues with shimmy as the excessive clearance on the bushing allows the spindle to continually change pitch , which changes the contact tire patch and effects the actual caster trail of the tire. So now you have two things to check.

Third is this shimmy instigated by a defective tire? If you have changed them side to side you only initiated the shimmy from the opposite side , you need to completely change the tire to another borrowed set. While your car is jacked up slowly rotate the tire faster and faster and eye the tread surface to a stationary point and do the same to the side wall. This will give you an idea if the tire carcass is defective. While it spins mark the tire when it stops at its low point then respin the tire and see where it stops a couple of times. If it stops randomly its in pretty close static balance , if it continually stops on the low side then there is a balance problem.

Now for right now the last factor to check is the toe in of the car, this should be no more than 1/8" to the center. Your spindles are machined for positive camber and that means that they run at true 0 with toe in. When checking toe in I usually recommend that you first disconnect the tie rod and position both hubs so that they are at a right angle to the axle. By doing this you can assure that the wheels are correctly pointed straight ahead. With the wheels straight ahead, you now can reset your tie rod to straight ahead and adjust to the correct 1/8" toe in.

Before you go any further try this and report back your results.

 

Dick is most likely on the mark. When I built my last hiboy I put 10deg caster in it for some stupid "excellent" reason I can't even remember. Maybe better wheel return. Anyway, as soon as I put it back to 7deg. it stopped.

 

The tie rod is not bowing signifigantly. I could see it flexing or bowing when I applied pressure to the wheels. I had the radiator off and had my face right in front of it. It was bowing. I have since replaced the radiator and I can not see the center of the tie rod any more. You could not possibly see it bow from this vantage point even if it was moving alot. If you can't see the center of your tie rod I am sure you can't imagine it is moving.

I have measured that I have 7 degrees of caster with an angle finder.

"Are you sure that you are not just seeing this rise and fall as the king pin inclination rotation angle changes the steering arm position ." - I am just putting pressure on the tires, there isn't any movement about the axis of the king pin to speak of.

I can't feel any shimmy or wiggle in the king pins. The passenger side has a slight slight slight slight slight click when I move it with my hands at the 6 and 12 position. The driver side has none.

I changed the tires for another set with different wheels with no change in the problem. It is possible I have two sets of bad tires. I don't know which side sets it off. Just a good bump or change in the pavement surface.

I have set my toe with toe plates and have 1/8" toe in. Typicallly I make sure the car is going straight by driving it in straight, then check the toe, then make adjustments.

 

Wednesday morning, Now more questions. Do you have 7* at static and equal on both sides? Remember the caster gains as the wishbone rotates under bump compression. So with a small load and soft springs you could go to 10* based upon your control arm radius. Rollout a couple degrees of caster and go for a test ride.

Now toe plates will give you toe -in or out but they will not tell you if the spindles are square to the axle. In some instances especially where you have replaced some components it is easy to achieve a misalignment when reinstalling parts. If the spindles are not square to the axle you can have the correct toe-i/out but have one tire leading the other as you have created a parallelogram measurement rather than a rectangular measurement. When the leading tire wants to return to center the other side becomes misaligned and fights to return to its happy center setting of a shimmy. Re check the square of the spindles. The same can happen if you have replaced or loosened the spring or it fits loosely in the spring pocket, if the axle has rotated slightly it will place one wheel slightly ahead of the other.

 

Will do - Thanks Dick. Hopefully all will be back together tonight or tomorrow.

 

This might be your problem. A couple of new bushings are cheap, it's just the three hours of labor to R&R.

Or, as Spadaro said, heim joints belong on the track. I think a new set of regular tapered tie rod ends and some forged steering arms (not flat plate) would eliminate a possible source of wiggle room.

Have you checked the bolts that hold the arms to the spindle? We had a bolt in a blind holed steering arm come loose once going down the interstate. Got kinda wiggly in the frontend, and made a scraping noise as the head rubbed the brake rotor. I think arms with through-bolts are safer.

 

that sounds crazy, have you tried putting youy toe to about3/16 ti 1/4 toe out,you don't give enough information, good luck, hotrod frank34

 

set toe out to 3/16 to 1/4

 

attn: Hot rod Frank your solution will grind a set of tires off in a hurry. Toe out on a positive camber spindle will produce a scrub as it drags the tire down the road sideways. It does a real good job of tensioning the king pin resistance as the tires try to pull them selves away from center.

 

Agree with Dick on toe out. Only thing I ever put toe out on was oval track cars. Helps them on "turn in".
Dave

 

well I just got back from one hell of a ride - the hot rod is back. No more death wobble. I stiffened the tie rod, set the toe to 3/16" in and put some spacers between the spring mount and the spring to make sure it wasn't bottoming out on the cross member. All is well. Any speed, any surface. Even the turmultuous GA back roads that are half repaired ready for paving didn't set it off. Thanks for all your help.

On a side note - my buddy who has the same speedway tie rod and drag link says he can flex his tie rod when he pulls on the wheels. Same exact thing. He says it slightly bows in the middle. His has not been driven on or damaged in any way.

Thanks for all the input from everyone. HAMMER DOWN!

 

Congrats! That's such a good feeling, eh?

What do you mean you "stiffened the tie rod"?

 

I welded a long piece of 1/2" and 1/2" angle iron to the tie rod. I think I need to get a good one from you. The new toe setting puts the angle pointing forward and you can see it.

 

That's great news!

 

I was sitting in my shop contemplating the Speedway tie rod on my latest build
which is not driveable yet.
I followed this whole thread and like most, found it difficult to believe that Tudor
could actually bow his tie rod by pulling on both tires at once.
He may be much stronger than me though!
I thought of one thing that I didn't see(?) mentioned that might explain the bowing.
It occurs to me that a perfectly aligned setup would result in the compression load
being exactly down the centerline of the tie rod and it would not bow without a huge compression load.
However, if the load on the tie rod was even slightly oblique to the centerline of the
tie rod, one end would be ever so slightly higher than the other end of the tie rod,
which it seems could promote the bowing described.
In other words, perhaps the tie rod is running uphill 1 or 2 degrees, left to right side.
Does that make sense to anyone?
I know the symptoms seem to have gone away with your stiffener and toe adjust
but I would still like to understand the bowing.

 

"I followed this whole thread and like most, found it difficult to believe" ???

I don't understand how it's hard to believe.

The heims should pivot as necessary allow for the force to act directly through the axis of the tie rod even if they weren't aligned the force would have to go through the axis of the tie rod. It is a pin connection. Regardless, I can tell you the steering arms are well aligned.

Like I said below, I have a firend that has the same tie rod and his does the exact same thing and it's never been driven on. Do you find that hard to believe too?

 

I made a bad choice of words...I should have said I was amazed like many others that you were able to bow the tie rod by pulling on the tires. Not that you lied.
Try as I would, I could not make my tierod bow by pulling on the tires.
Maybe my example was poor. I'm only an engineer.

 

Bigwoody, I don't know either, maybe its just that you can't see the tie rod when you are pulling on the because its under the car behind the radiator or whatever. I assume your car is fenderless? I never noticed it until I had all that off and had it exposed. I was going over everything trying to find something that was loose etc. Also remember you have two 25" levers when you are putting tension on the tires. It still didn't take much force.

My buddy had another guy get under the car and look while he was pulling on the tires.

 

Yeah...engineers seem to be no help here.

 

Actually Coolhand at the begining of the thread had a pretty good "Engineering" handle on it. He knew all about the Moment of Inertia which is what the tie rod did not have enough of. The angle I welded on incresed it's moment of intertia.

What kind of engineer are you?

 

EE/ME see profile staff designer at Microtune,Inc. ... and you?

 

so..to get to the bottom of this.(if i understood you correctly).end all be all it was the POS tie rod?

 

I'ver been following this for several days and if I have things in the correct chronological ordeer in my head, Josh, didn't you beef up the tie rod and stll had the death wobble till you increased toe in to 3/16" and shimmed between the spring mount and the spring?
If so, it may not have been the tie rod.
Dave

 

Could you take some pics from several angles and post them?

Not worried about the bend bit, but it would be interesting to see how the front end is set up.

Not sure why the Death Wobble went away, but I wouldn't be surprised to hear that it came back.


Note that I'm not calling you stupid.

Some problems are so far off the wall that they defy logical explanation sometimes.

Note too, only sometimes....

 

I screwed up becuase I changed 3 things at one time before I drove it.

I think the flimsy tie rod was the major contributor.

Since stiffening the tie rod worked, I think you can conclude that this is why people have success curing or masking their wobble problem by installing a steering stabilizer to the tie rod. Even though it doesn't act in same direction as the deflection, the fact that it's bolted on to the tie rod keeps it from vibrating out of control to allow the whole front end to go into the harmonic wobble once installed.

Bigwoody, I am M.E.