Technical The search for a cure-Death Wobble SOLVED!

"Billy's" are the shock of choice with rally cars. Being a Mono-tube there is more piston area so they don't "heat fade"
Whatever you do ....make sure the outer tube doesn't get any dents.

The reason too much caster is an issue , is because the lightweight nature of the vehicle.
The caster will find it easier to lift the suspension than to straighten the steering [made worse with too much scrub]
Add to that scenario, when one side lifts the shackle angle allows the axle to shift over to the opposite side [to a point of load equilibrium between the 2 sides]
This is also fed back through the cross steer also causing the steering to steer the opposite direction. [back'n'forth, back'n'forth etc etc]

Eliminate the axle sideways shift and you have won this battle .

 

I haven't driven mine, but on the shackle/shock mount deal? I just couldn't. Not only did I have clearance issues it just didn't "feel" right. Its axle travel that needs damping, not really spring travel. I made shock mounts out of heavy wall DOM and threaded weld bungs like for 4 link bars. I don't know how far along you are and I should look closer at your pics but here's what I did...

 

I’ll attempt to upload a video. If it works you will see the latest version of the death wobble. I am on vacation in a couple of weeks. I’d like to try and remedy this. You can see the speedo as it goes through the range. At 45 it starts to plane out.

 

That wobble is a tire/wheel/balance issue.

 

That is not the “ death wobble” that most folks are talking about. Death wobble is way more violent than that. What you have is a slight tire balance or out of round problem!






Bones

 

Deth Wobble you wouldn’t be able to make out the steering wheel or the dash! Certainly wouldn’t be able to video it! Lol

 

Don't listen to them, that totally is "deth wobbel"tm

 

It may be but the DW I experience is much more violent and I can't drive it out, rather I brake and slow till it stops...

Attempting a drive out just increases the shaking to the point that it feels like parts are gonna fly...

My situation is probably due to front bias ply tire issues...I know for a fact one tire has a slight side ways shift in it...it could also be the spring hitting the frame, steering box or some other mechanical issue...

I have balanced the tires with beads, weights and a damper which keep it relatively absent...I intend to replace the fronts soon...I hope that makes a huge difference...we'll see...

 

You had said, way back at the beginning of this thread, that you were getting the tire balance checked. Are they straight and balanced?

Do you have some spares with less offset you can try?

Are you going to change out the shackles for the Speedway ones with the long stud for the shock mount?

And I do think that spring is too long to not have a panhard bar on it. Either get a shorter main leaf, or a panhard bar.

 

Any time you have a wobble at an exact speed, it is directly related to the rotation of the tires, wheels and brake drum! Easily fixed, by finding out what is out of order.
This is what Roothawg indicates he has.
I f you are going down the road and hit a bump and your vehile starts shaking violently, and your steering wheel goes crazy and it doesn’t stop shaking the whole car until you almost stop, and you are in danger of losing control of the vehicle, you have just experienced “ death wobble” ! Not everyone has experienced this straight axle phenomenon! When you do…..you will not forget it! What Root Hawg is filming is not “ Death Wobble” !






Bones

 

I'm not so sure...it could be a much more passive form of it...

 

Every thing is relative! Root Hawgs problem does not approach the Death wobbles I have experienced. The true “ Death Wobble” is extremely violent and requires the driver to attempt to stop it as quickly as possible, to avoid damage to the vehicle and loss of control! If you ever experienced true Death Wobble, you would understand that it cannot be vidieod by the driver.
I have seen people that have experienced Death Wobble and refuse to ever drive that vehicle again! Put it up for sale, the next day!
Root Hawg’s steering wheel is moving maybe 3/4 of an inch back and forth! Totally in control. Irritating , but not life treating !





Bones

 

I have experienced the real deal you speak of...

Front end issues are difficult to diagnose...I understand that Death used in describing Roots front end shimmy is overstating a much more passive movement...as you say it's in a different league...annoying just the same...the other thing we don't know is what are his wheels actually doing...

Even though most of my death wobble experiences were at speeds below 30 mph stopped by quickly braking to a much lower speed...I had a couple at around 50mph when I hit a potential rim bending pothole pounding the tire/rim...that was equally violent in wobble...I don't believe I drove out of that either and it's really worrisome whenever it happens...

I agree regarding the damper they help bandage but are not a cure for the actual problem...

 

There have been hundreds of pages written about this problem. Many are helpful, some are not.
Ford issued service notes about this back in the day.
Literally EVERY part of the front end plays its part. Major things like wheel balance and tire pressure are easy to sort, so start there.
Than do a careful inspection for worn or loose components - check everything and put it right.
Caster, camber, king pin angle and toe in are all factors that need checking. Do not forget wheel bearings and king pins
If wheel offsets or diameters have been changed treat these with suspicion, may change toe requirement.
Remember two or three small faults can multiply into a big wobble.
That turned into more words than intended - I have worked through a couple of these, can be time consuming and frustrating but the is always a logical solution.

 

Keep in mind, this is way better now. Changing the steering box and the other things I did improved the wobble by 80%. This is what is left with a stabilizer.

I have experienced true death wobble. The Fly has it BAD under deceleration. People in the stands can see it.

I do think it may be a balance issue. I plan on jacking it and removing the tires over vacation in a couple weeks. I just don't get off in time to make it to the tire shop during working hours.

 

Hey Root, do you have another pair of wheels you can swap over to see if the problem stays or follows

 

While you have those wheels off, hold an indicator up to the hub and spin it. Check for concentricity.

 

I’ll have to look around. I don’t think so. Spindle mounts are all I have left….
I have a set of the same 15x5’s but no tires for them at the moment. They are still boxed up.

 

No, different pattern. It’s a 4.5” pattern.
Dad’s stuff is all Ford early pattern or Chevy pattern…..trying to think who might have a set of loaners.

 

I just finished working a wobble out of my newest build, a '31 roadster on '32 rails and can add just one more thing to this post: don't overlook the obvious...and don't assume anything. As was stated in Garpo's post, two or three small faults can combine into one big wobble.

One other thing I learned on my own car was that the common aftermarket dropped steering arms can play a big part in causing this problem. There is a huge amount of leverage created by the deep drop, enough to cause the thin-ish arms to flex slightly, and as mentioned before it just doesn't take much.

In the process of doing mine I switched to the Chassis Engineering style dropped steering arms which are much beefier and make the drop in two shorter stages rather than one long one. Pete & Jakes carries these and I highly recommend them.

 

I'm trying to remember what arm I used. I think it may be the CE arm.

 

Years ago I had the wobble bad enough to break my Rad core from the lower tank...3 times before I ironed it all out. Shaved my bias tires, that helped. Took to alignment shop, that helped, installed steering stabilizer, that helped. But the biggest culprit was my brake drums were out of balance. Made myself a balancer, balanced them with weights I made, and it solved all my issues. Rides nice with no vibration.

 

interesting. This has aftermarket discs on the front.

 

Don't cross the discs off the list until you have checked them. Spin a few times and mark where it stops - should be random.
Disc conversions usually move the wheel center line away from the king pin. May need to experiment to find ideal toe in setting.

 

I have vacation starting this weekend. I plan on pulling the front wheels back off and throwing a dial indicator on the rotors. I’ll take the wheels back to the tire shop and verify balance.

 

If this is with a stabilizer , you got trouble ! Mine is/was worn/ cupped front tire(s) , steering damper cures it completely ! ( but its a band aid. LOL
Here's how I look at it ; damper & install = $20 .
New set of front tires = $250.
Easy choice for me ....

 

It has all new parts. I am hoping they find a broken belt or maybe a weight that was thrown.

 

Speaking of which..............wife had a blowout on her OT daily. I pulled two wheels off and had new tires mounted for the winter. All looked good until Friday, she was freaking out on the drive home. I took the car for a spin and holey chit! Never heard such a racket. Limped it back home only to find out it had chucked 3 out of 5 lug bolts on the left front. Right side was hand tight. Pulled the wheels and BOTH were missing the brand new weights, found several Oz. of stick ons in the driveway. Darn thing tried to shake its self to death.

 

Ok. Time for an update. Been on vacation this week so I spent the day troubleshooting ye olde wobble of death.

Mama Root and I headed out early this morning to tackle this craziness. On the way to the shop I walked beside the truck and looked at the front tires while she idled along about 10 mph. I could see the front tires hunting back and forth, so I figured it was a toe in alignment.

I started with the low hanging fruit. I put it up on the lift and started looking at the basics. I started with checking the toe in. I noticed that the pass side was kinda kicked out rather than in. I thought for sure that would fix the issue. Better, but no bueno.

I ended up breaking all of the tie rods down and starting over. I started with 1/16” toe and experimented with up to 1/2”. The problem goes away with excessive toe, but obviously that won’t be sustainable.

I took the tires and dropped them off at the local franchise tire shop. They told me they had to rebalance, so I was excited thinking this was the ticket…no bueno. They installed a stupid amount of weight. I’m not feeling it. It sort of feels like it has humps in it at low speed. At 35-40 it’s most noticeable.

I am beginning to think the actual tires may be out of round. They are some cheap Chinese radials I mail ordered. I don’t have time to mess with it, but I may try and get new tires since it seems to be a consistent at 35-40 mph.

It’s better, but still not to my liking. I had to give up for the day. I had to put it all together, because I have to haul the Grand Marshal in our local parade tomorrow. Don’t wanna disappoint the man…..

I did throw a set of 2” blocks in the rear to get rid of that pesky gap between the fender and tire. Probably not the best time, but after being on the lift 25 times today, I figured oh well it s a freaking shop truck.
I have driven a straight axle since the 70’s and have never had an issue like this. It’s super frustrating.