Death Wobble - speedway tie rod may be suspect

Bumps don't change the direction of the car AT ALL - it is rock steady

 

Yes, just found them, thanks.

Except for the panhard bracket being on the opposite side of the car from the usual it all looks pretty standard.

I got the impression your steering arms were short, but they appear to be about the same length as the SuperBell arms on my 32.


14" wheels fwiw.



Off the subject a bit, but it looks like your calipers are rotated downward a little further than usual.

If I remember right, flopping the caliper brackets left to right and vice versa will do that.

My 32 fwiw.




Is the car easy to steer on the road?

And real easy to 'steer' when jacked up and the wheels off the ground?


I believe there are tapered bushings available to accept a bolt to adapt Heim Joints to a standard Ford tapered tie rod end.

That would be an area of potential slop in the steering if no bushing.


Color me . . . still confused....

 

SOrry my pictures aren't better, I had to use my phone.

C9 the caliper brackets were different from yours, they were flat plate and identical. so swapping them shouldn't clock the calipers.

http://www.speedwaymotors.com/Speedway-Complete-5-1-2-Inch-Disc-Brake-Kit-for-Early-Ford,1997.html

The steering effort is normal and feels good. The heims are all new racing Aurora heims with the dust covers added this time. These are much better than the original ones I had provided by speedway. Opinion/fact (cheap shot? not really) They were about 50 each and there isn't any play in them. The steering is very tight all the way up to the steering wheel.

Sorry this is so confusing. I am also trying to respond to everyone's comments to eliminate thoughts that cause further skeptiscism.

 

The steering set up you show in your pics is pretty much the same as mine except I'm using tie rod ends instead of heim joints.
The other major difference between your whole front end and mine is that my panhard bar is anchored to the frame on the driver's side and attaches to the pass. side bat wing. Dunno if this would matter.
But what do I know! My car is still under construction and has never been driven! It could come out slick as greased owl shit or it might be undriveable!
Just pointing out a setup difference. Mine was a rolling chassis and body setup from Brookville with a Pete and Jake's chassis. They have a bracket welded to the frame on the left side for panhard bar when you get the frame, either as a bare frame or as a rolling chassis.
Might it be that having opposing pivots foir the drag link with a fixed vertical pivot height on the left @ the pitman arm and the panhard bar having a fixed vertical height on the right side could induce some sort of wobble when the car heels over a bit in a turn or moves up or down on one side as in hitting a one wheel bump or pothole?
Dave

On edit: The frame bracket for panhard bar is at a length that puts the bar paralell with the drag link.

 

Dave it could be. I didn't come accross the fact that the genreal consensus was to mount the pan hard rod to the same side as the steering box until after I had done it all. I do know it doesn't bump steer and it worked well for a while. In theory the panhard rod should simply locate the axle and it should act the same moutned on either side. The axle would move in the same arc with the arm acting on it from either side.

 

Couple years back, we had a discussion on which side of the frame the panhard bar bracket should go on.

I've always read, heard and been told that it should be on the same side as the steering box.

Seems that the consensus from several was, it didn't make any difference.

And a few had them mounted to the passenger side.

Even so, I still put mine on the steering box side, front and rear.

 

ok here it goes..stupid question for me..
but its in an effort to learn, so thats a good thing..

does it matter pan hard on rear axle set up..frame anchor on drivers side..pan hard front axle ..drivers side also?..does it make any difference?
is this the "norm"

last Q...should you run one up front always?..or is this just a preference thing?

 

I remember that thread! You nailed the summarization. I had already installed mine and thought I'd just see how it performed. No bump steer.

Von, good questions. Looking forward to hearing what people think. I will tell you my rear PH bar is fixed to the frame on the passenger side as well. It tracks excellent under power and rides nice.

 

I was told to fix the pan hard on the rear to the drivers side of the frame due to torque/rotational loads on hard acceleration,and cornering, to aid in the planting of the rear end...fact? or BS?..it made sense..when i looked at it..but i have nothing but that "opinion" from some one else to back it up..think it came from some dirt track dude, and how they set up their rear ends.

sorry Tudor..i dont want to send your thread out to the dumpster for the questions on the pan hard...so i hope this thread doesnt get off on ,,well.. another tangent.
alot of good info here..and all i can say is i hope i dont have any of these issues to deal with when it comes time to roll in my A

 

no problem - it doesn't really matter Everything is just mixing in the bowl. It's a great discussion.

 

The one thing to try to remember is to keep the pan hard bar as parallel to the ground as possible. That way sideways movement from suspension travel will be limited. If you have it at an angle it will have a tendency move the axle to the side the lower mounting point is on which in turn will move the body to the other side. This can cause undesireable handling.

If they are parallel to the ground it really won't have any affect on the handling.



BloodyKnuckles

 

definetly..that same dirt tracker guy imparted that info to me also..he said best to set up the rear pan hard after you load the car how its going to be going down the road 90% of the time..ride height, axle possition, interior amenities (load)..or at least a best guess..that way its parallel to the ground in the way the car is going to set, as used/driven.

im sure that goes the same for the front panhard

 

it your 1937/41 steering arms from speedway? been problem with this before as not 7 deg it little bigger than 7 deg possible play slightly feel wobble when steering maybe not

 

The holes in the steering arms are not beveled like a stock steering arm. The are drilled straight through. The bolts are holding the heims very tightly and they fit without much slop. You can't feel any slop in them. I have had someone wiggle the wheel while the car is on the ground looking for slop. Nice 32 in the avatar man.

 

My total front end is from Speedway motors and a Mr. Roadster products. I have never had any problems and the set up bolted right in. Its all stainless and currently I have close to 3000 miles on good and bad roads and never any problems at all and center link is not giving in any manner to give wobble or tire shake.

 

Excellent thread, some really good comments, gives me plenty to think about, as I am in the middle of setting up the steering and suspension on a solid axle blown gasser street project. Axle, springs, tie rod came out of an old Ford truck. Drag link is 35" long and is on order from Speedway, so will check it out closely for quality and strength when it arrives. I prefer ball joint ends on my tie rods and drag links and stick with them on all my rigs. Yes, I can fab up most anything I need here in my own shop, but my time is limited, and raw materials here in Hawaii is mostly not available and is expensive to ship in from the mainland. Buying prefabbed parts that meet my specs saves me time and money and speeds up the progress of my projects. I have yet to receive a part from Speedway that was not completely acceptable. If this drag link is not acceptable, I'll send it back (although they say the "custom" links are not returnable) and fab my own. Or I could whack off the ends and use them on a piece of larger OD tubing to stiffen it up if needed.

I've set up the caster on this axle at 7*, and the toein at 1/8", it's a rear tie-rod setup, front cross steer. The springs are set dead flat, so I am hoping side-to-side movement will be nil or close to nil, and hope I will not need a PH bar. Will see how it handles once it's on the road. I've had some serious speed wobbles in the past and for me it always came down to looseness somewhere in the system, worn ball joints, incorrect alignment, stuff like that.

Never thought about the tie rod/drag link flexing, so will be aware of that now, interesting to think about how/what that could be about.

Like others have commented, it is difficult to visualize how that can happen, but apparently it can, so I need to be aware of it.

Lots of good comments here, took my time and read through the whole thread.

BTW, I am a mechanical engineer, retired, with over 40 years experience designing, building and operating custom farm equipment in Hawaii for the sugar and pineapple industries. Hot rodded motorcycles, cars and trucks are only a hobby, but a life long passion. A lot of the practical lessons I've learned from my farm equipment projects are applicable to these projects. I've also learned that the Chinese are just as capable of building quality parts and equipment as are the Japanese, the Europeans and the Americans. I've had some seriously crappy American made stuff in the past, so I just cannot condemn anyone's products based on where it is made. So far, Speedway has come through for me.

Aloha,
2Loose Willy

 

Wow I didn't think that this would generate this interest. Hey, Tudor look what you started. 777 I'm not beating you up, I'm jealous you've got a surface plate. Ok in between packing boxes and answering the phone I took some time to try and make a visual to see why this tie rod is getting the bows. Well by now most have figured out that the only way to bow a rod is with a force applied off center line of the rod. To replicate Tudors situation I tried to quickly duplicate his parts, I didn't have one of those steel steering arms so I just made one out of a firing strip for demonstration. Don't beat me up on this I have other things to do during the day.

The first step was to analyze what actually is happening as the spindle turns on the axle. I have a demo axle for a brake display so I just used parts to examine what happens to a stock spindle steering arm. I mounted a spindle at zero caster and rotated it thru a swing and then at 7* pos caster and rotated it to see what happened at the steering arm. See picture 1 and 2. If you examine the axis line drawn on the spindle vs the steering arm tie rod hole you will notice they stay very parallel and I think this is where the bow of the tie rod can now be explained. Meaning the force on the tie rod arms generated at the spindles seems to be on that lateral axis, horizontal and parallel to the axle centerline.

Now going to pictures 3 and 4 I have tried to duplicate the straight steering arms Tudor has on his car. Now by comparing the swing of the steering arms you can see that the straight arms tend to trail off downward as the spindle rotates. The effect that I perceive is that the force applied to the straight arm tie rod is directed in downward angle and circular motion and deflects away from the axle center line however there is a reactionary force that wants the tie rod to return closer to the axle center line and the fight between the two forces is neutralized as the bar bows and finds a happy medium. (Added 8/22) Thinking about this again, this bow could also be caused by the decreasing span distance as the tie rod arms locating holes converged during rotation and shortened the span of the the tie rod measurement mount distance. If the static measurement was 42" and the rotational measurement decreased to 41 7/8 where did the .125 distance go? Nowhere it just bowed the rod to make it fit.

Pictures 4 and 5 represent the stock spindle swing to the left a 7* caster and the relationship of the steering arm to the center line of the axle , you can observe that the axle does not exhibit a severe drop as the holes representing the tie rod bolts stay parallel to the axle center line and the resultant forces are not as great and do not deflect the tie rod.

I think Tudor and can solve his bowing problem by simply bending the tie rod arm bolt ends so they are more parallel to the axle center line.

777 I think you have almost the same problem but the wheel forces that you are experiencing are greater than Tudors due to your excessive caster angle and I think the whole thing turns into a math vectors problem. You have to downsize of that caster number.

In both of your cases its not the tie rod its the engineering angles that are creating the problem all you are doing is overcoming the situation by adding more mass to the part with increased size and sidewall. 777 I'm not in favor of running so much caster on a street car, I run 10-12* on the race car because its used to jack weight when turning and place it on the edge of the tires for better turning. The forces are also directed of the top of the spindle not the bottom so the forces are closer to the axle center line not further away.

There are a bunch of guys with ME degrees out here that might want to jump in, I slept thru physics, this is the best I can due to explain why your tie rods bow. How does it go "That my story and I'm sticking to it". How about some of you smart guys piping up I'm willing to learn something also.

Sorry could not figure out to insert pictures in text, numbering is left to right, pictures 7 and 8 just extra

 

I hope that somewhere in this thread Josh finds the solution to his problem. I know that this has been one of the most interesting and instructional threads yet on front end geometry on straight axles, which aren't nearly as simple as some would have you believe
Dick, your treatise on squaring a chassis and the axles and spindles has got to be the most comprehensive, complete and understanable write up on this important subject I have ever read. I printed it out to add to my private library of tech articles worthy of keeping on hand for future reference. Thanks.
Dave

 

I've been thinking about how a rod with heim ends could be loaded off axis enough to induce a bending moment, since the balls should always self center to apply the load along the axis of the tube.

However, if the ends of the tube are tapped crooked (IE the tap wasn't run into the tube parallel to its long axis), the heims will align the applied force to an axis parallel to, but offset from, the long axis of the tube.

While the moment induced would be a small percentage of the total, given a large enough initial force, the bending moment created could be large enough to cause deflection like the OP is seeing.

It could also just be as simple as the tube being right on the edge of strong enough for the slenderness ratio in play, which makes it want to fail in buckling (which happens at a total load far below what would normally be required to fail the part otherwise). If the tube is wanting to buckle, it will randomly deflect when loaded, even if loaded exactly on its neutral axis.

The latter reason is why I suggested he sleeve the tube he already had, as that would easily rule out stiffness as the culprit (if the death wobble happened with the fat tie rod, then its caused by something else).

It was a cheap and easy test to help him rule out one possible cause.

 

I've been thinking for an hour after reading Dicks last post. I have changed my opinion completely about a tierod flex contributing to wobble. I think Tudor and 777 are way ahead of most people like me.

Trying to keep this short... In 1971 at age 20 I bought my dream car, a fendered 30 mopar roadster that had parellel leaf mid 30s "wavy" tube axle. The seller gave me a wild ride on bad city streets with no problems. I get the car home and put on Keystone wheels with more offset. I did not get 1000 yards down the road to hit a cross culvert paved 'bump" with both front wheels...and my first death wobble.

Hotrodding was all but gone here in 71, and streetrodding had yet to start, so I was on my own trying to fix it. The original steel wheels were put on, but the wobble came back slowly. One thing I KNOW I did was to tighten those old style adjustable "spring & screw" drag link ends. That made it 100 times worse! So, now I'll bet by not having any "spring flex" in that drag link, the tierod MUST have been flexing more???

I never could fix that car and bought a parts car chassis to put it back to stock-restored.

Late 70s I built a twin to that car from scratch at the Tyrods club in Ct. I knew I wanted cross steer to maybe eliminate any chance of wobble. I cross steered the stock Mopar I beam with a 605 PS box. None of the guys there could find a correct right side tierod end with the "second hole" for a cross steer link....So, one member said Bronco used a solid rod with a spare hole. That Bronco rod was overkill in looks, as it was solid forged, maybe 1-1/8" dia...but that car never even twitched over culvert bumps. I did not set the caster at Tyrods, but drove it to a former clubmembers auto repair shop for the alignment.

So, now the way I am thinking is, that if you have maybe too much caster or too much of something else and conditions are "good" for a wobble to start, then a weak tirod lets it go nuts???

 

...and if the tierod is really flexing a LOT during wobble, then by adding a steering damper which is clamped very close to the center of the rod...does that damper prevent the massive flex in a tierod?

So we think the damper absorbs wobble, but it actually is bracing the tierod?

 

Or possibly, it's added weight is also dampening the rods tendency to oscillate up and down?

 

And one more thing.to add

I notice (and im sure it may have been brought up before)
But those flat steering arms..dont have any ackerman bult into them..they come off almost straight from the king pin..straight back...if you were to run an imaginary line or a string line thru the center of the king pin and the center of where your tie rod bolts into them..that line would end up pointing at your rear wheel..that is not good ackerman from what i have been taught..
that imaginary line or true string line should intersect back toward the center of your rear axle..
having no ackerman or reverse ackerman can also cause wobble and very poor handeling..of a straight axle car.

 

Ok purely informational stuff here. My front end is exposed really well and it has standard tie rod ends - not heims. I realized I have the same Speedway tie rod kit that Josh does, so we decided to do some observations. I got to say the tie rod flexes. I have the same one on my 32 truck and I have never had any death wobbles.

http://www.youtube.com/watch?v=A2L4Tc_VSTs
http://www.youtube.com/watch?v=OJirORzA2EI
http://www.youtube.com/watch?v=VjqlNoWV-PQ








And for all the flex haters

 

so is it the fact that speedway stuff ain't good or has Josh been taking my Bruce Lee strength pills?
I might have to hit the garage and flex my rod...or see if my rod flexes...or see if speedway sold me a rod that flexes.... that sounds better...

BTW, Nice Ass Josh!

 

Looking from here, the whole tie rod is coming up evenly due to motion at the tie rod end.

Optical illusion I'd say.



Many thanks for going to the trouble to set it up, film it and put it on You-Tube.

 

2nd movie sure looks clear enough to see some flex. It also looks like the steering arms do a little flex also.

We need a undercar camera on a car that has death wobble I'd be willing to bet the rod flexes in inches, not fractions.

 

Well, that "optical illusion" is allowing him to induce toe-in and toe-out by pulling and pushing on the leading edge of the tire, so it must be a real duzy.

 

Don't Ya just love it when A plan comes togather?

 

I would attribute that to a loose component in the front end.

Dog Patch would be able to tell us there.


Along these same lines, I held a straight edge up to the screen and I don't see flex, just the whole tie-rod going up and down.

As noted, it's tough to tell from here.