Revisiting The “death Wobble”

And just in time for Halloween too !
Because the wobble will shake you to your Bones !

So as I understand many folks are still encountering and experiencing “death wobble” for perhaps their first or even fifteenth time.
I encountered it very many dark moons ago.
Long before it had a name or a remedy and ong before cameras were in fashion.
So in order to learn and understand I had someone else drive my Jeep while I crawled out onto the front bumper to literally get a first hand look at the phantom condition.
Hang on for dear life if you plan to ride a bumper to see the death wobble up close first hand .

Upon initiation the problem was manifest.
I saw the repetitive toe in / toe out cycling of the front tires while simultaneously the front suspension moves up/ down.
And yes during severe wobble the front tired do leave the ground
So yes again it is VERY scary when it becomes severe. And once your Jeep has it you need to shake it of soon for it will only return and with a vengance.

The Willys “split tie rod system” is highly susceptible to this toe in/ out cycling condition.
And eliminating the split tie rod system is a near fool proof way to prevent the toe in/ out changes unless perhaps you have badly worn tre’s.
These Jeep’s certainly did not leave the factory with the death wobble.
The death wobble surfaces over time from normal wear and from tear.
The death wobble of the standard Willys with split tie rods can be cured by fixing the causes and contributors.
This is the list of causes and contributors to the Death Wobble encountered with a standard Willys system are ………

Unbalanced tires
Bent wheels
Wheel bearing play
King pin bearing play
Bad tre’s
Bad bell crank bearing
Loose drag link sockets
Play inside the Ross gearbox

Steering dampers are a temporary patch not a repair.
Changing to 1 piece tie rods with good tre’s are also a sure cure.
One piece tie rods can be added to the single or better yet the double knuckle arms.

Here is my 1953 with fully standard steering system with having double knuckle system plus button head knuckle studs.

 

Did it disappear like a ghost or into the Matrix?

 

I’d like to add my $.02 here, having worked at a shop where one of our primary jobs was to cure death wobble. A few points…

Worn out parts are rarely, if ever the cause of the wobble. Yes they allow the wobble to be worse than it otherwise would be, but something else is causing the chain reaction to begin and sustain.

When you approach and pass 7° caster, the chances of DW increase greatly. Think: wobbly shopping cart wheel. They have a ton of caster, and that wobble is death wobble. It’s the resonating frequency of that wheel’s size and weight.

The number one cause we found is tire imbalance, out of roundness, wheel imperfections, or warped rotors/drums. A tire that has been perfectly balanced statically (on one plane) could still be extremely out of balance dynamically (on two planes, or diagonally). This diagonal imbalance forces the tire to want to spin on a plane that isn’t parallel to the hub. When the perfect speed is reached, the resonating frequency is ideal, and death wobble appears.

I’ll try to get to the rest later if I get time…

 

I still experience this on occasion.. I have tried everything but new tires or getting them rebalanced.

 

Soooo, in how many early Jeeps is 7 degrees of caster a problem? I have yet to see one with that much. I would agree tire/wheel/balance imperfections are probably the number one initiating factor, especially so on modern linked suspensions. But so too is Willys' genius 2 piece tie rod arrangement that provides that initiation potential EVERY time the suspension moves. Ken hit most of the high points but the spring/shackle bushings/u-bolts are also contributing factors once DW is initiated.

 

Some very helpful information in this thread.

I am not sure about the difference between cause and effect but rebuilding the steering is one of the first things I do when putting an old Jeep back into serviceable shape, right after rebuilding the brakes.

My thought is all of these things need to be put right.

I agree that the singe tie rod conversion is one of the best upgrades for the system, but the stock split tie rod system works fine if it is put in good order. When I was tending to the steering on my 47 I happened to have a military surplus front axle which has heavy duty tie rods, so I just swapped that axle under the Jeep, I rebuilt the bell crank, drag link, and Ross box. I used nearly perfect M38 wheels, mounted and balanced new tires, and new shocks. I checked alignment using the method Ken showed in an older thread. I doubt I have driven this Jeep over 40 MPH, but it steers fine and I have experienced no sign of wobble.

I don't like using a "stabilizer". I have found those on just about every old Jeep I have owned and that gets tossed when I rebuild the system.

 

The CJ5 in my avatar picture has two hole knuckles (both sides), but still has the split tie rods. It is a low mileage Jeep and drives fine the way it is, but I plan to convert to a single tie rod and will do the stud conversion on the knuckles next time I service the king pin bearings.

 

Just throwing this out there, In 1976 bought a 76' K5 Blazer new, and it came from the factory with a "steering stabilizer". After 50-60K miles, it got death wobble, replaced the stabilizer and no more wobble.

 

a stabilizer just masks the wobble, doesn't fix it. if there's wobbling, something is loose/worn out or unbalanced.

 

I have no doubt the stabilizers do help reduce DW and they are on every "new" Wrangler from the factory. They DO NOT prevent it. My JK developed DW with only 30k on the odometer with the factory wheels and tires. I replaced the track bar bushing and heim joint along with a Currie drag link and tie rod and that did cure it. That said, absolutely no excuse for that at that mileage in a nearly new vehicle. POS it was-from day one.

 

I saw someone in a pretty new looking jeep gladiator (the jeep truck) hit a bump and go full on death wobble as they slowed down to the side of the freeway. I only caught a glimpse of her face, but she didn't look happy

 

I never had the DW issue with the BFG KM3's 7.50-16's until I recently moved to Firestone 700-16 NDCC's, which I assume is exacerbating the underlying issue.

Items of note:
1. I replaced the front springs about six month ago back to OEM because the PO had removed one from each of the front leafs for the rears, he said due to weight of spare tire.
2. The front u bolt threads cross threaded when I was removing to replace springs, in a pinch since no OEM on hand, I used universal u bolts to same measurements from O'Reillys. One thread cross threaded near bottoming out, so that is suspect. Also there is one OEM ubolt that is different than the other 3 to account for the Dana 27 front transfer case flange it mates to, I now have that on hand but need to order the other 3 OEM style.
3. I installed a Tightsteer early on as the rest of the Ross was rebuilt but still loose, may need a new sector with the John Deere pins. The TS helped out, I know it's a BandAid but it does help until I can find a new steering shaft and replace the sector shaft with a beefier one, completing the steering box rebuild.
4. The PO rebuilt the steering/Ross box, not sure of the brand/quality, I would like to move to single tie rod setup, Herm will build me one with the OEM specs vs the Saginaw he normally offers
5. My death wobble seems to occur with the wheel turned and uneven ground. If I stop it goes away and may not reappear until I again turn on uneven ground. I also adjusted the wheel turn stops back in since I no longer run a 7.5 tire, maybe I have them turned in too much which contributes to the DW?It usually comes on from a dead stop with wheels turned and the ground is uneven, like backing out of the gravel driveway or a turning at a stop and the ground is uneven/pothole or a dip.

6. I will have another alignment shop check behind the last for alignment and for wheel balance just to rule that out. I did notice the Firestones seemed to balance out with far less weights than the previous BFG KM3's. I took that as a sign the less weight of the tire 30lbs vs 54lbs of BFG attributed to that and perhaps higher quality control? Iunno, just a thought.

7. I have Nolathane shackle insert kits enroute

 

New Ford 250-550 trucks have steering stabilizers from the factory. They've had a recall to replace them with heavier duty units.

 

Death wobble normally occurs while traveling at road speed, after hitting a bump. I'm not sure what you've got going on while backing up out of a driveway.

 

Speaking with my mechanical engineering hat on. Everything is a spring and everything has mass. As a result, everything has some resonant frequency. All it takes is a small cyclic force near the resonant frequency to make it oscillate uncontrollably.

Just like your suspension, your steering is a classic mass/spring/damper system. It's just much stiffer.

There are four basic ways to tune these systems:

1. Change the stiffness of the "spring". A stiffer spring raises the resonant frequency of the system. In this case, things like switching to a single tie rod, having more resistance in the steering box, having stiff suspension bushings, higher tire pressure, ...etc raise the resonant frequency. It may be possible to raise frequency high enough that normal road inputs don't excite it.
2. Change the Mass. A larger mass attached to the spring has a lower resonant frequency. For example, adding large, heavy wheels my bring the frequency down to where it now gets excited when it didn't before. A Jeep that was fine with 31 inch tires may have death wobble with 35 inch tires. Other than tires/wheels, there isn't much you can change here.
3. Change the damping of the system. To those saying a stabilizer is bad, you are wrong. This is one of the proper ways to tune a mass/spring/damper system. Try driving a car with no shocks on it! A properly tuned damper can completely prevent the resonance of the system while having little effect on slower frequency stuff like turning the steering wheel. Sometimes the engineering freedom of the rest of the system isn't enough to prevent death wobble in all situations. In cases like that, a damper is exactly the correct solution (like the Blazer example from Ollie2009).
4. Reducing the inputs that excite the resonant frequency of the system. There is a lot here. This is where true wheels, true rotors, balanced tires, smaller tires (for less leverage), no slop in the system, not having too much caster, ...etc. all come into play.

In real life, tuning the system usually involves a little bit of all the above.

Let me reiterate. Do not be against steering stabilizers. Do you hate your shock absorbers? Are your shocks "masking" your bouncy suspension?

If you care, Here's the math for the most basic mass/spring/damper system: https://en.wikipedia.org/wiki/Mass-spring-damper_model

This is not true. My '69 has a fully stock Ross split tie-rod system with no stabilizer and has never had death wobble. My CJ-2 had fresh Saginaw steering with a one-piece tie rod and would occasionally get death wobble. This would imply that a one-piece tie-rod is not a surefire cure. It will likely help, but as noted above, sometimes the solution is complex.

 

We experienced this condition on a brand new 84 CJ7 with factory spoke wheels and Goodyear Tracker tires.
Customer stated it first happened to them at around 600 miles. We drove this vehicle over 100 miles.
Couldn't duplicate condition and alignment, balance, wheels, tires, shocks, steering, suspension etc. gone over with fine tooth comb.
Finally found a set of RR tracks that crossed a paved road at a 45* angle where it would happen every time.
It would erupt every time going east bound over the tracks at 50mph; not once going west bound.
Huh ?
We swapped another set of tires and wheels off another new CJ7.
Problem still occurred, no change.
I'll spare you the frustration of hours spent, and parts swapped chasing this condition.
On a lark, we swapped both front factory shocks from another new CJ7.
Nothing appeared wrong with the shocks we removed. Both felt the same while compressing and extending by hand.
But to my knowledge, it never happened again after swapping the shocks.

 

Well I also stated that the one piece tie rod must be used with good TRE’s to be effective. I’m just saying that it typically one of the most reliable effective cures.

TRE slop can allow the toe in/ out cycling.
Yes good stabilizers can be a remedy but it is also true that no known factory stabilizer ever existed.
And like I said these Jeeps likely never had wobble when they left the factory.

True yes all the steering slop is not the cause. But that is exactly what allows the resonating imbalance to become manifest. The trigger is the imbalance such as segmented highway bumps and imbalanced rolling mass.
And yes the suspension also has an influence.

I’m saying that in large part the wobble scared the crack outta me to actually see up front what was going down.
Specifically the Extremely Bad Vibes were visually apparent.
Death Wobble is the perfect description !
If not stopped, the complete steering system can be trashed.

 

my 2000 F250 doesn't have a stabilizer, pretty sure it didn't have one from the factory either