Technical The search for a cure-Death Wobble SOLVED!

Man, you ain't lying. It's too early for me to comprehend. I'll need to wait til, at least, after lunch.

 

I know the difference .
The triangulation pertains to articulation ,not positioning , IMO
Wobble can be caused by any number of or combination of conditions on a solid front axle vehicle , " solve" one cause & another may take its place . If OEM engineers can't solve it , always & permanently in all cases , all we can do is try . For those of you that say ," Oh I solved it " that's great , for your circumstances , if you have the holy grail of repair for everyone's problem , you should be very wealthy as selling the secret formula would be worth a fortune !

 

It's just a theory of mine. I think it makes sense, but I have been told that I work a little different to most folk.....

 

I'll take a look at it. Never really thought much about it. I basically use the same formula on ever 35-36 I build. 57-59 Ford rear or 55-57 Chevy rear with a 235 70-15 tire The fronts all get the dropped CE 46" I beam axle with a disc brake kit and the 15x5 Wheel Vintiques with about 2-1/2" of offset. I try and center the wheel.

Now I am curious.

 

I tried those needle bearing on my truck.
Let us know how they work for you when you look at them in a few years

 

I bought a standard set of king pins and bushings. just in case.

 

Hello,

Any wobble is too much. Why fight the steering wheel while cruising down the road? I would first check the round specs of the tire. "get all tires trued" The amount of tires that are not round is amazing. Someone was asleep at the wheel, in the factories. But, that amount of rubber on the ground will show you how much it needed to shave to get a round tire. Now, balancing and check the wobble.

If you are at a tire place to balance, have them spin the rim and tire and see if the metal edges go wobble or not. If so, you need new rims. Some people will “fight to the death” to get those round, but it is not fun nor does it always work. It is easier to get new rims and start the process over. But, at least your tires are round.

Now, if all else fails, have an expert front end alignment guy go over everything. In my first 40 Ford Sedan Delivery, I had to get the tires shaved first. I though I lost about a 100 miles of rubber on the floor. But, afterwards the balancing and shaving worked. The 1940 Flathead Sedan Delivery ran fine for 1000's of miles of coastal cruising.


Jnaki

The second 1940 Ford Sedan Delivery with a 327 had more front end problems than the old Flathead powered one I had in high school. The first thing the alignment guy said was to get the tires shaved with the steel rims in place. So, I did and again, 100s of miles of rubber was on the floor after all of the tires got shaved to “round.” Then a bubble balance to get the sedan delivery back on the road. It drove smoothly and there was no shake. Then about 6o miles later, close to home, the wobble started again. We even had installed new shocks and it felt fine.


By this time, we had our own expert alignment service tech that had completely fixed the Impala, the first 40 Flathead Sedan Delivery, the 65 El Camino and now, sitting in his huge new alignment shop in the OC was our latest problem handling hot rod. A 327 powered 1940 Ford Sedan Delivery. He took it for several days and did almost everything he did on the other cars we owned. Lines drawn on the floor, measurements galore from front to back and side/side, each individual reading on his machines and calibration tools, etc.

It looked like a doctor with all of his tools splayed out on a nice blue shop drop cloth, along side his chalk and measurement devices. Since he had a new shop, he did have some new equipment. But, he did rely on his training in the old school ways and for the last thing he tried, was to balance the wheels and tires using an old “on the car” motor set up balancing machine.

The one thing he told me to do before I got to his shop, was to get the tires trued and round. Most people just don’t want to think that their tires are NOT round, so they skip this part of the fix.

Then, the expert went to work doing his magic. After the long days, he told me the sedan delivery was fine and come back to his shop for a test drive. It rolled on the smooth streets in slow speeds and on the open highways past his shop at speed. No wobbles, shimmy motions or jerky handling. It drove like a sports car grabbing the road around corners and like a real car driving down the road with no external forces allowing the sedan delivery to sway or not. No, damper was necessary as the whole Ford front end was set up correctly, it just needed the fine tune by someone that had the expert skills to make it work.

NO steering damper is necessary if the alignment and necessary new parts are installed/adjusted correctly. But it all started with correcting the not true or round tires, radials or even bias ply. They were new, but not round.

The expert front end alignment/wheel/tire/chassis repair guy's advice was to enjoy driving such a cool hot rod and that try to avoid going over pot holes or huge dips at speed. One well placed hole in the street does wonders for the tire alignment and sometimes balance… Well noted and for the next several years, he checked everything and it was the best handling hot rod we had driven. My wife liked it so much that somedays, I was alone at home looking at her 62 Corvair and she was out doing errands or visiting friends in the 40 Ford Sedan Delivery.

Most home builders have the techniques and knowledge, but someone who does it for a living just has those extra things that we normally don’t do or have the skills to get it done correctly. YRMV.

 

twenty8 - I worked on all areas of the front end when I had the problem. So because there was more than one possible cause I figured I would eliminate them all while I had the car apart so I cannot point to one specific thing as THE problem or THE solution.

2old2Fast - I am not sure who your are addressing with the comment about the cure all? What I am reading and what is offered up in my case is the things that worked for me. At no point do I suggest it is the cure all for anybody else's problem. Simply suggestions of things Roothawg might take a look at that he may not have considered.

 

Need new everything to be sure, Kingpins and bushings, steering rod ends, 3 to 6 deg. of caster, lower front tire pressure say 21lbs, new steering box, solid mounting for the steering box, 1/8 in toe in. fix all of these things and you'll be set for a while til the next wobble happens, add a steering stabilizer and it'll be fixed even if the parts and pieces are old and loose. Auto parts stores sell a steering stabilizer kit for 50's Ford pickups that work well, ugly but gets the job done.

 

Try checking your caster at both ends of the axle. I fought a death wobble for a couple of months. Everything was tight, the axles were square to the chassis centerline, etc. No adjustments were making any difference. I bought an angle finder with a digital readout and checked things again and the caster on one side was 1.5 degrees more than the other, which was hard to detect on my old craftsman dial angle finder. Apparently, the wishbone had been high centered on one side, because there was a slight bend in it affecting the caster angle. Once I fixed that, the car never had a problem. My guess is that when the car would hit a certain type of bump, the axle would kind of gallop.

 

THAT is a good angle (pardon the pun) that I have never heard before!

 

As fare as the toe in. IF YOU JACK THE TRUCK UP AND SCRIBE A LINE ON THE CENTER OF EACH FRONT TREAD YOU CAN MEASURE TOE VERY ACCURATELY.
I've got a set of those toe in bars that came with a set of turn tables that even have a pair of matched tape measures to check both in front and in the rear of the axle at he same time and that is fine for a guy setting up dirt track cars or working by yourself but scribing a line on the tread and measuring from line to line with a helper who can hold the other end of the tape to the exact spot on the line each time is going to be more accurate in the long run. Scribing the line compensates for any wheel runout or tire side runout. You do not need to waste a frigging bunch of time making something that may or may not be as accurate as what you can do with a pencil and tape measure.

Tire balance, the tires really need to be spun up on the truck to see if anything in the wheel, tire, hubcap drum/rotor-hub assembly is out of balance.

Anything loose has to be corrected, that should be done without question. Why would one leave anything loose?

 

The problem, sometimes, is you cannot get to the center of the tire with a tape, so you have to measure lower on the tire ! Can give an inaccurate reading…..sometimes!






Bones

 

With todays cheap lasers you can rig up two parallel lines pretty easily how ever far out from the fenders you need. Somebody did a tech on this

 

Lasers! Where's the tradition in that? I'd much rather crawl around on the dirty floor with my 60 year old trammel bar and some tape measures.

Maybe the tenth time I adjusted my toe, I got a little smarter. I wrote down the amount of toe adjustment I got from a certain amount of tie rod turn. Like if I turned it a quarter turn I got 1/32 of adjustment (probably not accurate, just an example, I'd have to go look at my notes). At 18 TPI, you do the math.

 

Another thought: I just pulled my spindles off my sedan to do a brake change. They had been on there for 10,000 miles, with fresh kingpins back then. I found a few specks of brass from the bushings had stuck to the kingpin, and caused scraped ridges in the bushings. On the sides where pressure of the spindle sat from weight on the wheels. I had greased them every year, about every thousand miles. But I didn't jack up each wheel to take the pressure off as I greased. I will be doing that from now on.

Maybe the OPs needle bearing kingpins won't have this problem.

 

Its usually the top taper tha gets worn. I've put a large washer under the perch pin and that would tighten it up . JMO

 

That is usually the case, a combination effect of causes.

Agreed......

 

Did you make up your own tie rod and drag link?
If so, were the tubes cut with a saw and checked for squareness?

I've had my cross steer front end mis-adjusted every which way and only had death wobble once when I totally mis-read my tape and had over an inch of toe in.

I recently came up with a theory on why I've not had more trouble. When I made up my links, I cut then on my bandsaw and then true up the ends on a lathe. I believe that any slight amount of out of square to the thread centerline causes distortion and stress of the link when the rod end jam nuts are tightened. When you hit a bump this stress gets turned into the oscillations mentioned before. Just my opinion.

Gary

 

Ok, death wobble! I have been dealing with this for sixty years, for the first part of that I just lived with it, went slow, missed bumps hit the brakes , mostly on farm trucks! Straight axles are straight axles , wether they are on a truck, car, hot rod or t-bucket! They all have to live with the same physics!
About twenty five years ago we took delivery on three identical trucks, they came off the assembly line , 1,2,3! After they were in service a short time one truck, I will call truck #1 started the wobble when it hit the railroad tracks in the center of town! It came it to my shop as an unsafe truck!
I started by checking to see if anything was loose….nope! So I took it to our go to truck front end shop and they checked it over….perfect, nothing loose and proper alignment! So…..I thought it must be the tires! I bring in truck #2 , switch tires and wheels…..the problem stays with trunk #1! I take truck # 2 to the front end shop , it checks out with the exact same alignment as truck #1!
Well, what now I thought? So I go to the oldest guy in the front end shop and he gave me two wedges to put under the springs to tilt the axle, changing the castor 1 1/2 degrees!
Success! No more wobble! So I go back to the front end shop and tell the old guy I tilted the axle to give it 1 1/2 more degrees! He jumps on me and says I put it in backwards! But it fixed the truck, it is still in there today!
My point is everything can be correct or as correct as possible and some vehicles may still wobble! These were factory systems, not a hot rod! Sometimes you just cannot find the smoking gun on this problem! So you just have to change something a little and castor is the easiest! Cambor not so much!
Since that time I have “ fixed” many “ unfixable “ straight axles by adding or subtracting the castor to maybe one degree out of specs!
Just my experiences.





Bones

 

You always need a straight shot from wheel to wheel, and ideally it should be as close to 3 and 9 o'clock as possible to be accurate. But that's also often impossible unless you have an offset device that allows you to put it at 3 and 9, yet drop down to miss anything that's directly in the way.
I've got a setup I built from angle iron that offsets the angle iron down about 6" but still allows the ends to contact the wheels at 3 and 9. The angle iron is two pieces, so easy to clamp them together with vise grips once I've got it spread out against the wheels. Don't need anything fancy, just something that's sturdy and works.

 

And the irony is you are typing it on one of these new fangled computers, the internet is a fad!

 

Chris: As a reminder, you may come across times that Toe-Out is the answer.

I have built a few cars that 1/16" - 3/16" of toe-out cured my issues. As we know, there are so many variables in the components, tires, caster, chassis rake, wheel off-sets that following the preconceived rules of alignment doesn't always apply.

 

Boneyard51 mentioned that in a pm. I may very well try it.

 

Generally , toe out will make a car wander , albeit perhaps barely , but wander just the same.

 

Which brings us nicely back around to too much positive scrub radius (wheels too far out).
Think about it. You can have 1/8" static toe-in dialled into your alignment, but the forces created by too much positive scrub can cancel it out (or even get into toe-out) through component flex/wear.
I hope a light bulb has just gone on..........

 

Toe-out is needed to counteract "camber thrust" caused by having negative camber. ( think of 2 cone shaped wheels driving towards each other)
Most hotrodders are risking "death wobble" the moment they bolt on smaller diameter wider wheels.
This increases the scrub radius (so the wheel has a tendency to toe-out when it hits a bump)
Then they increase caster to counteract this.
The problem with this is it becomes easier for a lightweight vehicle to lift than to straighten the steering.
Once the wheel travels through the bump the caster snaps the wheel back and usually "over corrects" to the other side (starting oscillations back and forth)

A heavier vehicle is less prone to death wobble than a light vehicle.
Start with adding more back-spacing to the front wheels, and backing off the caster a bit.

All the advice of "more caster" is adding to the problem.

ALSO check the rear wheels for run-out (the wobble could be transferred down the chassis and the caster is correcting it)
A good example of this is death wobble in a fuel-altered after a burnout.[they bounce from side to side on the slicks ,and have a huge amount of caster]

 

I should get some shop time this weekend. I am curious about the scrub deal…..I’ll take some pics.

 

FWD cars have a lot of negative scrub radius.
This reduces "Torque Steering" on corners.


If you look at the positive scrub radius example, You can see how smaller modern wheels will increase the positive scrub radius [And old vintage wheels are ideal]
Unfortunately King pin inclination is not adjustable, but wheel offset is.