Technical Violent front end shaking

Is your tie rod in front of the axle, or behind it?

How much weight is on the front axle?

What size are your front tires, and how much pressure are you running in them?

What size are the front rims, and what is the backspacing?

What are you running for front brakes (brake offset)?

What are you running for links to the front axle, and what angle are the at? Do they run up to the frame from the axle, or down as they go towards the axle?

What is your steering setup?

How about some pictures?

 

I did see his post, but "I" cannot explain why. Normally, a "tight anything" on steering, like a king pin, will cause dramatic wander on a straight uncrowned road.

I even wondered, if he accidently bent the tie rod with the jack, but I doubt that.

Another thing from reading your post; we sometimes are not all talking about the same types of wobble. There is another poster up page one, and his description hints more towards a tire balance problem. People whom have never driven a car with death wobble, can easily think they have, due to tire hop, odd balance issues at higher speeds, etc.

If we read all the older threads here, some oldtimers recalled " just living with DW",and having the balls to "drive through it". Meaning, this being a very low speed event, and contrary to our first instinct of braking, they nail it, which rapidly turns the wheels/tires into gyroscopes, which kill the oscillations. (yikes).

as backyarders, we have the gift of modern, fast, info on the net that reaches out to people like Dick and Kerry. These guys were/are circle track or road course drivers/builders. They had the option of peeking at their competitors cars, or learning about everything they could, that would give them the racers edge.


I hope someday to see Ford caster explained. I looked up in an old MOTORs Manual, to see that Ford I beam specs for alignment checking damage/etc, was 4.5 to 9 degrees, I think the chart was 35-up? Anyways, most USA cars were on independent suspension around then, but the ones that still had a beam were 1 to 2 degree, and only one car at 3 degree. Why is Ford so much?

One of the last D.W. threads with Dick online, he suggested using the minimal figure
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I found out on my truck ('38 Ford with stock front end) that wheel offset had a huge effect on handling. Midsize GM discs on front, was running 15" steel rims from an S10 Blazer, swapped for '80s Impala 15" rimswith less offset, steering effort was greatly reduced and handling became much more predictable when I hit a pothole or railroad crossing. One thing worth remembering if you're running a bit of a rake or big and little tires--raising the rear or lowering the front has the effect of tilting kingpin inclination forward, reducing caster. Raising the front or lowering the rear has the effect of tilting kingpin inclination backward, increasing caster.

 

To clear up terminology...
Some readers might see the KPI spec in manuals and get confused.

KPI is not anything to do with caster setting specs.

KPI is the angle of the king pin when viewed at the axle, but standing in front of it.; or.. looking directly at the back of the axle.

as you know, ("positive") caster angle is seen by standing on the side of the front axle, seeing the tilt leaning towards the rear of car

 

F&J, top or bottom? "seeing the tilt leaning towards the rear of the car"

 

My tires were out of round so I had them trued and rebalanced .No more wobble I already had installed a steering dampner.

 

1956 i had a 34 cutdown that would get the death wobble, i would just drive it with one tire off the road on the dirt, stopped it every time, SIMPLE.

 

Try driving a car with the shock absorbers removed. You can get the same initial up and down movement that can transfer from back to front and corner to corner similar to the way the steering does in a death wobble. I will disagree that the damper is designed to reduce shock. The only way you would get sideways shock on the draglink would be in a collision. The damper is designed to dampen harmonics just like the crankshaft damper on an engine.

 

please explain in which direction "sideways"on the draglink. Hitting the link broadside, or trying to compress it?

If you do mean compression shock on a draglink, then yes, there is shock applied to compress it. That is why the early types of draglink ends as well as pre-1935 Ford tie rod ends have springs...to lessen the impacts.

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The bad thing about internet researching, is that you can find a site that backs up a persons belief, but the next site backs up an opposite belief.

Here is a quick copy/paste:
Shock to the Steering System

• Road hazards such as a blowout or an impact with debris can create a violent reaction in the steering wheel. Steering stabilizers prevent this jerking action. By absorbing the impact of unexpected jerking, the stabilizers will also prolong the life of ball joints and other components in the steering system. Much like regular shocks that absorb sudden impact on the suspension, steering stabilizers absorb sudden impact on the steering system.
• ------------------------------------------------------------------------------------------------------------
• I don't know why my text is showing "dots" below...ignore those
• 
  Can we also talk about those spring dampers on the older drag links and some tie rod ends? I ran across a very interesting front end design from a 1934 Cad/LaS chassis; This is either the first or maybe second year for the new independent front suspension on this brand.
• 
  
• Very odd setup, almost a half breed type of steering linkage design. It still uses a side steer box poking through the frame like old beam axles had, pitman arm still pointing down, but they reversed the worm direction, and had the drag link run angled inwards up to the center of the large front suspension crossmember.
• 
  
• the draglink then connects to a 1-to-1 ratio L pivot lever, to convert the side steer, to become a cross steer, by having twin short tie rods to each wheel. The point about damper springs... this drag link does still have the old spring setup on each end, but the twin tie rods instead have modern style conventional unsprung, non adjustable/sealed ends. So the designers still felt the need to have something to diminish road shocks to the steering box and steering wheel.

 

Wow..........a simple picture to start , I-beam,6 to 8 pos Caster, and regular tires ???????? Should work
fine!

 

Okay I had the 34 to the alignment man and he said the toe was way out. I took it out and hit the bumps that caused it initially and everything seemed fine. I will have to drive it for a while until I feel safe again. He also told me that the drivers side rim was slightly bent but he did not seem to think it was part of the cause. I also had him balance the tires while it was at the shop. I am going to drive all weekend and will update for you all. Thnaks!

 

GLAD YOU FIGURED IT OUT! I THINK THAT IS WHAT I NEED TOO?

 

Well I thought it was ok. Went out today and I just knew it was
not gonna be the end of it. I went over the RR tracks where this first happened and it did it again. So in review: the front end was aligned by a professional, he said the left front rim was slightly bent, there is some play in the 56 For steering box. But I have drove this car for a year and a half with none of this happening. What happened. Please advise. I will be putting up some pics soon.

 

Got better pics? Pic from squatting in front of one wheel, to show us the imaginary centerline of king pin, as that line intersects the pavement. I see discs, and those push the tire centerline outwards from the KP line....which degrades the proper "scrub radius".

If scrub is off, combined with unfriendly Caster setting...can be a problem.


did he give the current caster setting if he had it on the alignment rack?

If not, take a pic that shows how far the axle is tilted back at the top if possible.
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I will see if he had the caster number and I will take the pics you need tomorrow . This rally has me bummed out to say the least. I'm kind of scared.

 

I never have said on hamb on why I read all the death wobble threads for more info...

in the late 50s I started building car models, and somehow got hooked on early type hot rods. That's all I dreamed of...a hot rod. Turned 20 years old and found a 50s full fender roadster for sale in town and had to find a way to own it.

The hoodlum tough guy owner much older than me, let me give 200 deposit and the other 600 in 2 weeks..

He took me for a wild ride through the worst bumpy city streets and I hung on grinning. He drove it to my house when I paid up. The first thing I did was bolt on a pair of 6" deep dish mag wheels on the front. I snuck it down the road with no registration....and 100 feet later I hit a diagonal bump from a buried cross culvert.. I thought my life was ending, no idea what was happening. Hit the brakes and it got worse till it finally came to a stop.

I did toss the mags, but it would still do it once in a while, as I must have bent something. Over 6 months it got so bad, I drove it for the last time when crawling over a soft bump at 25mph, it went berserk and shook the hood top off, one door upper hinge unhooked, and was hanging, and the windshield frame fell out of the windshield posts and fell on me.

All I ever dreamed of went to shit, and back then, nobody could help me figure it out. I've tried to learn more since then.,,,and I still don't know enough IMO

one thing Dick never wavered on was refusing to use a damper as a band aid, because there IS still something wrong. I feel the same way.

I think he was OK if a car got fixed first, then add one for shock damping. That may be the only way you will feel safe now?

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Others have wondered what changed in the time you had been driving it ok.. Me too..

Just my feelings with not enough info, but I think your car was a borderline problem child, and something finally changed enough to get the wobble.

^ I don't drive with worn steering since my early days. If your car came to me, I'd do this: Disconnect the drag link from the pitman. Now go lock to lock on the box, to find half-way true dead center. That is a machined high spot on the worm gear. The freeplay can only be properly set at that center, and that must be centered when the front wheels are 100% dead ahead.

if you cannot rid the free play at the true worm dead center, I think you will find slop at the outer brass bushing behind the pitman arm, That causes the sector shaft to rock front to back during free play.

You should be able to see that slop right now with all connected, and weight on the tires. Rock the steering wheel back and forth, but only in the free play, to see it better.


the other odd thing is that you first said about a brake hanging up. That got my attention also. Others might chime in about if that could be something involved in this? I wondered if it would affect a marginal setup in a bad way?
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I'll put my two cents in here since I built the frontend. The car was setup with 6 degrees castor and everything was either new or tight. I would suggest you have the Gemmer box adjusted. There are a number of excellent threads on here how to do it as that would be the logical item to have somewhat loosened over the last 1500 miles because it is the only "used" item in the entire front end. The car is (was) running Firestone 16" bias which are not the most forgiving tires on earth but should be fine as I checked them for round and balance while they were here and were just fine. The geometry on the frontend is dead on so I would eliminate the Ackerman and castor/camber stuff except if you may have really hit something hard, like a curb or street plate that may have bent the axle, (not as uncommon as you think) giving unequal camber from left to right. This will give you the described condition. Many times alignment shops skip this on straight axle cars as they assume the axle is right. Also toe in should be 3/16" on this car. Many alignment shops set them to shallow as they are used to alignment specs on modern cars which use way less toe in than the oldies. This will also cause the problem.

Wish you were closer, I could probably sort it out pretty easy. Glad to see you're getting miles on the car. As a side note, we had the car to around eighty on 895 which is a combination of straights and sweeping curves and it handled really nice so whatever this is it's something new so that's where I would start looking, on the things that may have changed a bit.

 

Koz, I don't know you, but you as the builder will most likely be offended with anything I say at this point.
Before I start...., the last pics; my impression was that I saw the bones tucked in a bit and thought"this is not a typical poser build" "someone was thinking".

We can't establish that from what is shown so far. I see discs, and to the best of my knowledge, discs will trash the scrub radius. Scrub radius is a very major ingredient in wobble in my opinion. See Kerrys post early in this thread.

My point is, that if a front end has something wrong right from the start on design, we are looking for a compromise to side step that. I agree something has changed enough to go over the line to DW

just some bits that don't mean much, but tire balance really does not contribute in making a good build get to a death wobble, nor is it a factor in cars that do have geometry issues and do wobble. Most DW comes in/starts at such slow speeds, that the tire would need to be measured in pounds off, rather than ounces off.

and on topic of speed, the fact it did 80 has nothing to do with DW. Like was said earlier, brave souls can accelerate as they feel it coming on, and drive right out of a wobble. I don't have the nerve.

 

Have been this road myself. After years of use my 32 decided to shake its head at times, usually after hitting a pot hole.
Back in the 30s Ford issued a service note about this. Every part of the front end can be part of the problem. Tire size- offset- pressure - balance - wheel bearings-king pins- steering joints-shock absorbers along with all the alignment stuff. On my car I went right through the front end, fixed a couple of very minor faults (wear) and followed up with a very careful setting of toe in. Problem gone.
None of the things I fixed could really be pointed at as the cause, more an accumulation of several small faults causing a big shake.
The only answer is to systematically work through the front end, and ensure everything is 100% where it should be.
Garpo

 

Finally ! The voice of reason , systematic diagnostics instead of blind spectulation , great post !!
dave

 

I agree 100% on everything being suspect, not just one thing. However, the
Ford bulletin didn't need to address the mix and match parts, split bones, incorrect scrub radius, draglink angle, etc, that we deal with. Everything is not where it should be on this car, because it's a modified rod.

So, are you saying all the others posters here should not post anything ? Is the car fixed yet?, does he know what to try? or how to set things? Maybe you didn't mean it but that's how it sounds to me.
Dick Spadaro was the systematic voice of reason on these things. He went to college to be a school teacher. He learned the front end issues from his hobbies of race cars and old time rods, even giving seminars at big shows, and people like myself with ASE certification on front ends, received tons of knowledge that simply cannot be had by just being a certified mechanic, like the "alignment shop guy" down the street.

The OP's car just went to a front end shop and they missed something. I have no clue if they checked caster, camber, or "toe out at turns". All basic things that show up easily on a rack. Most people don't realize that "toe out at turns" is actually a test of proper Ackerman, and can even detect one side being off, which indicates a bent arm. Most people don't realize a car going straight with 1/8 to 3/16 toe in, immediately goes to "toe out" as the car starts to turn. All part of geometry..and physics.
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Could you post a picture of the front spring setup? [Crossleaf showing shackle angles]

Now to add to the confusion...............Check the rear suspension condition including shocks
I'll explain why.

Front caster is "height correcting" so when turning a corner there is lift on the inside wheel and the opposite on the outside wheel.
If you had a car and let air out of one rear tyre [lowering that side] the steering will pull to the opposite side. [oval track people see this with weight jacking]

This can best be observed in a drag car like an Altered with solid rear suspension and lots of caster.
When they do a burnout and suddenly shut off the throttle the torque reaction [or sudden lack of] causes the car to rock on the soft rear slicks.
The rocking of tha chassis causes the front caster to wobble the steering. Under full throttle the torque reaction only loads up one side and is quite manageable.
So give your rear end a quick check over, you might have an issue at the wrong end

And please post a picture of the front spring setup

 

No offense taken on any of the above F&J! Death Wobble is a problem for everyone from the Ford factory to home builders. When I discussed driving the car I wanted to note that the car ran not only at high speeds but through most other road conditions. I use 895 here for that reason, (including rail track crossings). The car was also driven by the licensed Pa. inspection mechanic in a somewhat spirited manner. This little sucker ran nicely. This is something that has changed since the car was built. All I wanted to put on the table is that the geometry of this car was of a somewhat typical Ford build. The car had some serious rust problems so we elected to remove the front clip, (including the knee action), and replace it with a front end more typical of a '34 Ford or something as the owner wanted to run open wheel.

The first thing I would do is start front to rear and check every single component for damage, frame, mounts, 'bones, rear end hangers, everything. In particular check all connections as DW will rip a car to pieces. There's a lot of good information in this post. This should not be too hard to find. If Joe wants, I have loads of construction pics of the front end.

 

I agree 100%

 

I barely drive the car to 50 and have not hit anything hard so we can eliminate that. It does happen and happen when I go over a particular set of RR tracks here in town and not going very fast. Thanks to Koz I have had a fun car and just hope to figure this all out soon. You guys have given a lot of info, can somebody just refine it for me? I will check all the components front and rear to start.

 

Several have asked for certain pic views, take those outside from different viewpoints.

In the meantime, you mentioned "free play" at the steering wheel. Koz and many others have said freeplay needs to be looked at, and must be repaired.

I did post how to check the box to know if bushings are good/bad, and how to tell if the box is really properly centered to the "straight ahead position". As far as complex adjustments of play in the box, the worm play rarely needs readjustment. That would show up as the steering wheel/and inner steering shaft, is moving up or down. In other words, the steering wheel moves up towards you, or down.

You cannot set the sector shaft adjusting screw until the worm gear is at true center of the worm itself. You cannot set the sector adjustment if the sector bushings are worn. In cases of abnormal wear in a box, there always is a possibility of the worm being worn at the true center position, but you can't tell until you try to set the freeplay.

If the worm is bad, you won't be able to feel the high spot as you turn the adjuster in, and keep checking the steering wheel drag a half turn either way. If the worm is good, you will feel a slight friction, as you move the steering wheel from 1/2 turn off, back through the true center. This friction test is with steering disconnected or the front wheels off the ground.

If there is no point at which this friction happens, the worm is worn.

I'm not saying box play is the only culprit, but if there is play in the steering or suspension, it must be eliminated.
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