How can I figure out why I have death wobble? (1 Viewer)

[bjp]

I have a 1993 with death wobble that I've tried to fix and it's still not fully gone. I'm sure there are many things I could blindly try if I had infinite money, but how can I figure out which one is actually likely to fix the issue?

I know this is a bit long, so to encourage responses: I'd be excited to send $50 to whomever first describes a diagnostic procedure which leads to diagnosing an issue that, when fixed, solves the problem. Just throwing out things it could be doesn't count unless accompanied by some test I can perform to confirm or deny whether that thing is actually the main problem before spending money and time addressing it.

When it started
I'm completely new to Land Cruisers and vehicle maintenance in general. I bought this LC in March with 163k miles and I've been baselining it ever since, so I've put less than 1k miles on it. I thought I had the minimum set of stuff done in September so I took it to an offroad picnic about an hour away by paved roads. Just before hitting dirt, I got my first death wobble around 30 mph. I thought "that was crazy", but the pavement was a little rough and I hadn't heard about death wobble before, so I did a bit of light offroading then started home. A fire forced me to take (paved) back roads for 23 miles and I got probably 8 or 9 wobbles. By the end, I was trying to intentionally trigger them to figure out what the trigger was, and I was trying various things to mitigate them instead of just braking hard, but I couldn't find any reliable patterns.

Behavior
The wobbles always started between ~20 and ~55 mph -- I took it carefully on the freeway on the way home after the wobbles on the back roads and got zero wobbles on 28 miles of freeway, then one more wobble on the 1.5 miles between the freeway and my house. The wobbles seem to be more likely to happen while on a slight curve (especially when the curve direction changes), when hitting small bumps (but larger bumps don't seem to do it), and when slightly braking, but even a combination of all these factors doesn't guarantee a wobble, and not all factors are necessary to produce a wobble. Again, I could never figure out when they would or wouldn't happen.

Initial investigation
When I got home, I found the jam nut of my front adjustable panhard rod completely disengaged, so I tightened that jam nut. I could grab the drag link or tie rod and rotate them on their axis by hand fairly easily, but I didn't feel any play. I jacked up each front wheel one at a time and tried to wiggle the wheel while grabbing at 12 and 6 and I didn't feel any play. I tried to wiggle while grabbing at 3 and 9 and did turn the wheels a bit, but didn't notice any play. I took off the mud guard of the driver front wheel and looked at the frame and panhard tower around the steering box and didn't see any cracks. I measured 30.15 PSI in front passenger tire and 30.65 PSI in front driver tire, and both wheels still had balancing weights attached (though I can't rule out some falling off). The two of four knuckle nuts I could easily access with my torque wrench were still torqued to at least 71 ft-lbs and the other two were "tight" (both sides).

After tightening the panhard jam nut, I took it back out on a 45mph street and got 2 more wobbles within 3 miles. A member of my offroad club diagnosed needing new rod ends.

Attempted fixes
I bought the Trail Gear Heavy Duty Steering Kit which includes a new drag link, tie rod, 4 rod ends, and a steering damper. I took off both rods, damper, and the steering box and had the steering box professionally rebuilt. The old steering damper was pretty much entirely done -- spring only, virtually no oil resistance. When reinstalling the steering box, I replaced the high pressure hose with Gates and the low pressure hoses with Gates from phhkit.com. I installed the new tie rod and used two aluminum angles to set 1/8" toe in at 37" wheel diameter, using two laser pointers to center the steering:

I installed the new drag link and tried to center the steering wheel as closely as possible using the two laser pointers on my alignment jig shown above. All crown nuts torqued to 67 ft-lbs plus whatever was needed to line up the cotter pin holes. The Trail Gear rods use jam nuts and do not have any indents to put a wrench on (!), so I tightened the tie rod jam nuts to TG's recommendation of 75-85 ft-lbs using a giant 14" set of vice grips and a giant adjustable wrench. I tightened the drag link jam nuts with just the wrench to "medium tight" because I knew I would need to adjust the steering wheel position a bit more. I did NOT install the new steering damper because one of the bolts was missing and Trail Gear has STILL today not delivered that missing bolt (they blame PROcomp, the steering damper manufacturer), but my understanding (which could definitely be wrong!) was that the steering damper just masks the issue and is never the root cause, so it seemed ok to leave it out initially. I also got my front wheels professionally balanced. Unrelated(?) to these fixes, I also installed a new Tom Woods DC front driveshaft.

Results
After these fixes, I drove a 38 mile loop including 23 miles of paved mountain roads like the ones that triggered so many wobbles. Zero wobbles. I did feel some "incipient shimmies" (vibrations like the ones that preceded death wobbles) which worried me a little, but I don't know the truck super well so I figured those may just be normal solid axle stuff. Given that I got 2 wobbles in 3 miles before the fixes, I thought for sure I would see wobbles in the big circuit if they were still a problem. The drag link did come loose from its jam nuts during the circuit because I hadn't done the final tightening yet, but even with the drag link working its way loose, still no wobbles. So, I considered the issue probably fixed and moved onto the next work.

Going to the picnic, I also had the AC shut off from overtemp while climbing a steep freeway grade on a hot day, so I did a bunch of cooling work next including replacing all of the heater hoses, replacing thermostat, replacing fan clutch with new 95F/6500cst-modded clutch, replacing radiator, and adding a temperature sensor to the upper radiator hose.

I went to do a short test drive to also re-set the drag link properly and...got a death wobble a short distance before my house. Well crap. I finished dialing in the drag link length and tightened the jam nuts to basically the gripping limit of the vice grips, then drove the same 38 mile loop. No death wobbles, but still a bunch of "incipient shimmies".

So, I don't really know what to do. I don't think tightening the drag link jam nuts should have made the difference between wobble and no wobble since I wasn't getting wobble on the big circuit even when the drag link was loose. But, it's also now apparently hard to actually reproduce the wobble. I feel like I can't take the LC on trips because I'll probably see wobble at some point since it was still present after all the fixes (not taking it on the trip I'm leaving for today because of this).

Configuration
When I bought the LC, it already had:

• 37" Cooper Discoverer STT Pro tires with most of their tread life remaining
• Method 105 beadlock wheels
• OME 419 Comp Coils in front, unknown OME coils in back, resulting in ~5" lift based on DeltaVS's panhard bolt method when lightly loaded (but still have front & rear bumpers + winch on front + full-size spare on back)
• Front sway bar removed
• 5.29 diff gears (net result from 37" tires + 5.29 gears = truck travels 92% as far as speedometer/odometer thinks it went, so slightly lower gearing than stock)
• Air locker front, Detroit locker rear

Not very many miles before the picnic, I installed new DeltaVS radius arms for a 4" lift. I tried to get before & after caster numbers, but no shop around here will measure alignment on beadlock wheels, and I gave up trying to measure the caster accurately.

I had recently removed all wheels (one at a time), deflated, carefully and progressively torqued all 120 beadlock bolts, reinflated, and reinstalled.

Both the previous owner and the one before that are members of my offroad group (I joined shortly after getting this truck). The previous owner had a bunch of stuff put on the truck (including air locker), but drove it only a few hundred miles over 2 years. The second-previous owner (an experienced amateur mechanic) said the front axle "is basically all new" -- he said he thought he did the rebuild at 13Xk, but based on CarFax, I don't think he owned it until 145k (he works on a lot of cars, so not surprising his memory may not be perfect).

Possible things to try
I can think of a number of things that hypothetically might address the issue:

1. New non-beadlock wheels + new smaller (35"?) tires
2. Knuckle rebuild, including new wheel bearings
3. Install steering damper
4. Add a front sway bar
5. Replace some of the front axle components (not sure which ones)

I'd be happy to do any of these to fix the issue, but doing all of them would be very expensive, especially when it seems like there's no guarantee that even doing all of these things would fix it. #2 seems like the leading candidate to address any wheel bearing problems, but it seems like the fact that there's no play in the wheels wiggling at 12 and 6 would suggest that the wheel bearings aren't the issue (plus, the wheel bearings were probably replaced 20k ago). #3 will probably "help", but if it were just hiding the underlying issue, that seems like it would actually make things worse by making the underlying problem harder to find. Could #4 actually affect death wobble? I'm not sure what I would be targeting in #5; are there any components that might be causing the wobble? #1 seems like the most likely solution (but I don't really know what I'm talking about yet), but $3k-$4k is awfully steep for "most likely". I want to get non-beadlock wheels eventually in any case, but I really like the Coopers and would like to keep 37s if I can figure out this death wobble issue.

Thanks for reading; thoughts?

 

[-Spike-]

Well, looks like it's time for me to pay the Piper, as they say. I started to have a slight DW few weeks ago and now it has become a predictable thing. I immediately thought of this thread and started to chuckle to myself when the steering wheel started to shake. Even though my panhard bushings are less than six month old and the front radius arms are less than one year old, I got DW .

I'll raise the front end today and check out the knuckle bearing pre-load as well as check the torque values on all front suspension hardware. It never ends......

and @bjp, just in case you never solved your issue, I didn't read the whole thread to find out if you did or not. (and nice job of getting your original post to show at the top of every page, neat trick )

Long story short (don't look ahead, just trust me, this is the short version), I have fought with death wobble a few times. Once it was a loose panhard bolt, once it was loose bearings (wheel and/or trunnion), once it was suspension bushings, once it was cracks around the frame by the panhard mount. I have come to know the 80 suspension pretty well. The last time I had the issue, none of the usual suspects were the problem. Tight suspension bolts, no play in wheel or trunnion bearings, new bushings, new tie rod ends, new shocks, knuckle studs torqued properly, rebuilt steering box (again), I added even more reinforcement around the frame panhard mount (everyone who wheels an 80 should inspect this area, cracks are common), I even went to extremes to make sure my wheels were perfectly centered on the axle hubs. Early in the process I also had my tires balanced at Discount Tire as usual, and trusted that they did it right. SPOILER ALERT: This turned out to be misplaced trust.

I had addressed everything that could be an issue. The only thing I hadn't done myself was balance the tires, but how hard could that be to do correctly? Discount does this all day long, they must know what they're doing. I did some research online and found that many people have had issues getting Toyota wheels balanced correctly. I'm not sure that it's a problem specifically to Toyota wheels, but 'Toyota' was one of my search terms, so I got stories about Toyotas. The problem came down to getting the wheel centered on the balancer. The way to verify there is a problem is to have a tire/wheel assembly balanced, then loosen the clamp nut on the tire machine shaft, rotate the wheel about 180 degrees on the shaft without letting the shaft rotate, re-tighten and re-test. If the machine now says it's out of balance, then it's very likely that the wheel hub wasn't properly centered, either during the original test or the re-test. There are tools that make centering the hub easier (Toyota has even put out one or more TSB's on the issue), which some shops use. Most don't, because they are expensive. They aren't really necessary, but they do make the job less reliant on the tech having the knowledge and making the effort required to do it right.

My life experience has convinced me that I can't trust anyone to do anything right (sometimes including myself, but that's a bunch of stories for other days- this is the short story, remember?). So, I bought a tire balancing machine (and got a tire changing machine in the deal), and a bunch of weights. At over $2k (for a cheap one, I should stress), it was a desperation purchase, but I couldn't think of any other way to get hands-on with a machine to do some testing and figure out exactly what the issue was. Besides, I do like me some tools.

Being a skeptic when it comes to, well, everything, but especially Chinese tools, I tested the machine by balancing a normal-size trailer tire, then I loosened the balancer shaft clamp nut, rotated the tire 180 degrees on the shaft, re-tightened it, and ran the machine again. It was still balanced, much to my relief. The 'cheap' machine actually did what it was supposed to do. So I moved on to one of my truck tires, which had just been balanced by Discount. It wasn't balanced. I marked the location of the weights necessary to balance the tire, rotated the tire, and ran it again. It came up with a whole different set of weights and locations. So, I was doing something wrong.

It turns out it is easy to screw up when balancing large tires. I have 37" Cooper STT Pro's mounted on Hutchinson beadlocks- a particularly heavy combination, around 150 pounds. My earlier research let me to believe that maybe I wasn't getting the wheel hub centered on the balancer shaft, so I thought about that. Big weight, hanging vertically on a shaft. Likely the mass was biased towards the bottom side. I loosened the shaft clamp nut, supported the weight of the tire on a floor jack, and re-tightened the clamp nut very firmly, forcing the hub adapter to wedge in as far as it would go in the wheel hub. I ran the machine, marked the required weights, rotated the tire on the shaft, retested, and got much better results- the retest indicated I needed very similar weights at the same locations as the first test, confirming that I was now getting the hub properly centered. I then removed Discount's weights, ran the machine, added the suggested weights to the tire and repeated the testing process a couple of times to make sure I could get consistent results on multiple runs.

After finding out how difficult and critical it is to center a very heavy wheel on the balancer shaft, I went a little OCD and polished the balancer hub adapters so they would slip into the wheel hub with as little friction as possible (thanks again @richardlillard1 for the use of your shop lathe). I balanced the rest of my tires and went for a test drive. No death wobble, problem solved. Lessons learned. Tools and skills obtained. Stupid amounts of money and time invested on what should have been a relatively easy problem- so business as usual for me.

Now, I'm not saying that all death wobble is due to bad tire balance, or that everyone needs to buy a tire balancer. However, tire balance should not be eliminated as the cause of death wobble just because you had the tires 'professionally' balanced. Those professionals are usually kids who usually work with tiny little tires, many of which would probably run down the road just fine without any balancing. And don't count on special balance equipment to be infallible- it doesn't matter what equipment is used if it's not used properly. Also, there is a difference between static and dynamic balancing, and most tire shops will perform a static balance on large tires, because it's easier and people are lazy and time is money and all that. Unfortunately, the bigger, wider, and heavier the tire is, the more critical it is to have it balanced side to side to keep it from wobbling, which is what a dynamic balance does. (On a side note, tire balancing beads and other methods of internal balancing do not balance the tire side to side either- been there, tried that. They work fine as long as the tire/wheel doesn't have major side to side imbalances, so you can read about lots of people who use them with no problem, and also lots of people who didn't have success. I have been both of those people at times.) If you are having trouble with death wobble (and really, even if you're not), get your tires dynamically balanced, even if you have to pay more. I have read about specialty 4x4 shops that charge $50 per tire for balancing large tires- and after doing the job myself and knowing that they might spend $10-20K on the machine and adapters, I can understand why they charge so much. And techs at 4x4 shops are more likely to know how to do the job right. If you want to be sure they are properly balanced, convince your tire pro to reposition the tire on the shaft and re-run the test. If they've done the job correctly, it should still be balanced. If it's not, you may have to suggest a few methods, such as pulling out the fancy wheel adapter the shop may have, or supporting the tire weight while tightening the clamp nut. Or just tightening the clamp nut more than usual. Be warned, they won't appreciate being told how to do their job.

Or, maybe you need a new tool in your shop.

 

[mudgudgeon]

Overall I find it odd that everyone says that the giant rotating masses on each wheel (tires) and the damper installed to reduce harmonic resonance induced by those giant rotating masses are not really causal. If I were to do it over again I'd START spending money to solve DW with known quality tires that have a nice round profile (installed with road force balancing). If that doesn't help you can always use them later so it's not a sunken cost. In my experience most of what I was chasing around in my suspension/steering components were symptoms of DW and not the cause, including the cracked frame, bent steering arms, bent radius arms,

There's more than one cause IMO.

I don’t think it is possible to say there's a single definitive cause.

For everyone who's eliminated the problem through balancing tires, there's many others who have not.

I think you are right that the heavy rotating mass of wheels and tires is a contributing factor. As is the flex in tire sidewalls, and the effects of inertia trying to correct a bounce in the tires.
Ever try to rotate a running 9" angle grinder, so the blade is rotating on a different axis? The inertia of the rotating blade needs definite effort to twist the grinder to a new position.

The cause, or trigger of death wobbles is a bump on the road, or something that causes the tires to shift out of the neutral, straight line position. A poorly balanced tire in your instance is probably creating enough wobble to cause the oscillation in the steering.
The flex in tire sidewall on hitting a bump bounces the tires/wheels back the other way. The tires/wheels then oscillate back and forth.

Any play, or looseness within the suspension and steering allows a greater uncontrolled bounce. Momentum takes over, and there's nothing to control it.

I've never noticed death wobbles occuring during a turn. It's always in a straight line when steering is in a neutral position, and there's no load or tension on joints in the steering and suspension. While turning, there is lateral load on all joints, so play is taken up in one direction.

The steering damper is absolutely not a cause. It's there to try to control bump steer. It is a reactive device, it attempts to control a bump/bounce that has already occured. IMO, the amount of wobble is not enough to really engage the damper, even for a brand new damper.
An inch of movement at the outer circumference of a tyre is going to translate to a fraction of an inch of movement at the track bar, rod ends, and damper. Even less at wheel and trunnion bearings. Even if the damper is able to control ¼ bounce at the track bar, you can still have looseness in rod ends, bearings etc that the damper is unable to have any effect on at all.

 

[toyotaboy80]

Might be apples to oranges but my 1985 pick up with nothing other than leaf springs and shocks connecting it to the frame, lifted, 35 12.5 15 bf km2's mounted on steel bead locks balanced with beads and also have run 35 12.5 15 AT's mounted balanced traditionally on steel wheels. It tracks dead straight, 1 finger on the wheel 75mph on the highway and 1 hand on the wheel tracking forest service roads at 30mph never fighting it. The steering wheel has never felt out of my control. Smooth as glass to drive.

Sometimes the simplest things are denied or over looked, and can cause headache. I cant see solid in spec rigs having such a mysterious problem. Theres gotta a be a fairly identifiable problem and solution.

 

[GeoRoss]

I had a bad case of death wobble a few years ago that was initiated by braking at speed. The cruiser had sat for a year. Balancing and rotating the cupped tires helped a bit, but didn't solve it. All suspension bits were torqued to spec and I couldn't detect any play in the wheel bearings. Before parking the cruiser I had no indication that the front discs were warped.

I did a full front axle rebuild, new birfs, bearings, drive flanges and front discs/pads. Problems solved even with the cupped tires. I am sure I could have done some more investigation instead of the parts cannon, but the axle seals needed to be replaced. Then I found the birfs a bit worn and that required new drive flanges. I don't know the exact cause of my problem, but the parts cannon solved my death wobble.

 

[alia176]

I had a bad case of death wobble a few years ago that was initiated by braking at speed. The cruiser had sat for a year. Balancing and rotating the cupped tires helped a bit, but didn't solve it. All suspension bits were torqued to spec and I couldn't detect any play in the wheel bearings. Before parking the cruiser I had no indication that the front discs were warped.

I did a full front axle rebuild, new birfs, bearings, drive flanges and front discs/pads. Problems solved even with the cupped tires. I am sure I could have done some more investigation instead of the parts cannon, but the axle seals needed to be replaced. Then I found the birfs a bit worn and that required new drive flanges. I don't know the exact cause of my problem, but the parts cannon solved my death wobble.

Thanks Ross for the feedback and I think your experience is going to be the rule, not the exception. I'll check everything because it has been a long time and see what I discover, if anything.

 

[jellis]

@-Spike- brings up a really good point about tire balancing, I also figured out the hard way that shops are CRAZY variable. I've had multiple shops tell me that my rims were bent, others that they're true as can be. This is including different Discount Tire locations across, say, Las Vegas in one single day as I limp my way to my destination attempting to get my rig driveable again.

The early model 80s utilized LUG-CENTRIC rims whereas late models are HUB-CENTRIC rims. Tire machines are designed for hub-centric mounting and require adapters to do proper lug-centric mounting. If you have lug-centric rims, make sure your tire shop has those adapters and uses them when performing your balancing. The first shop to tell me that my rims were bent didn't have those adapters and said it didn't matter and would come out the same either way--but obviously not. The last time my tires were balanced I made sure to have the tech specifically check for bent rims, he said they weren't which to me indicates he mounted the lug-centric rims in the machine properly, and lo-and-behold these tires have been a dream and cured my DW.

 

[mudgudgeon]

@-Spike- brings up a really good point about tire balancing, I also figured out the hard way that shops are CRAZY variable. I've had multiple shops tell me that my rims were bent, others that they're true as can be. This is including different Discount Tire locations across, say, Las Vegas in one single day as I limp my way to my destination attempting to get my rig driveable again.

The early model 80s utilized LUG-CENTRIC rims whereas late models are HUB-CENTRIC rims. Tire machines are designed for hub-centric mounting and require adapters to do proper lug-centric mounting. If you have lug-centric rims, make sure your tire shop has those adapters and uses them when performing your balancing. The first shop to tell me that my rims were bent didn't have those adapters and said it didn't matter and would come out the same either way--but obviously not. The last time my tires were balanced I made sure to have the tech specifically check for bent rims, he said they weren't which to me indicates he mounted the lug-centric rims in the machine properly, and lo-and-behold these tires have been a dream and cured my DW.

Is easy to mount lug-centric wheels off centre on the car too.
Take a little bit of care to get them seated nicely.
There's been more than once I've bolted wheels back on in a hurry and found them off centre and causing vibrations.

 

[alia176]

Back in the day, Discount Tires (DT) used to use "fingers" for all Toyota hub centric rims for balancing. I see now those fingers are gone and something else is being utilized for Toyotas. They work well as I have three Toyotas with balanced tires but I'm always curious what mechanical tech they're using now.

I'm guessing by now, all DTs are using the Hunter balancing machine with built in road force separate roller. Guess we don't have to pay extra for the road force balance anymore as they're done with each tire, at least at my local DTs. YMMV.

 

[-Spike-]

@-Spike- brings up a really good point about tire balancing, I also figured out the hard way that shops are CRAZY variable. I've had multiple shops tell me that my rims were bent, others that they're true as can be. This is including different Discount Tire locations across, say, Las Vegas in one single day as I limp my way to my destination attempting to get my rig driveable again.

The early model 80s utilized LUG-CENTRIC rims whereas late models are HUB-CENTRIC rims. Tire machines are designed for hub-centric mounting and require adapters to do proper lug-centric mounting. If you have lug-centric rims, make sure your tire shop has those adapters and uses them when performing your balancing. The first shop to tell me that my rims were bent didn't have those adapters and said it didn't matter and would come out the same either way--but obviously not. The last time my tires were balanced I made sure to have the tech specifically check for bent rims, he said they weren't which to me indicates he mounted the lug-centric rims in the machine properly, and lo-and-behold these tires have been a dream and cured my DW.

Just for the argument, the only functional difference between early and later 80 wheels is the type of lug nut they use. The hubs are the same size with the same design, so they are all 'hub centric'. The early wheels use acorn style lugnuts, which, if installed with care, can center the wheel on the lugs as well as the hub. What's interesting is that the 'better' method is the one Toyota (and most other car manufacturers) abandoned.

 

[toyotaboy80]

It costs more money to have the hub and lugs on the same center. I have aftermarket steel wheels that are lug centric. You can see the hub pulled out of center as you square it up on the lug nut. Probably the result of s***ty manufacturing tolerances and a out of square stamp. This isnt inherently a problem as long as the wheel is true to the lugs and it is balanced on the lugs.

For a machined aluminum lug centric wheel, I would imagine the hub is machined on the same center as the lugs as the tire mounting o.d. should be able to be balanced lug or hub centrically and produce the same result.

IMO Mounting the wheel with an anglular nut interface is superior to a flat face nut clamping the wheel. In any event the tire mounting OD has to be square to the method of location on the vehicle and it has to be balanced by what is square to the OD.

 

[toyotaboy80]

I wonder if the term "death wobble" is used properly in this thread.

As far as I understand, death wobble is there every single time on dead flat road accelerating up to speed and can be accelerated through. Induced by lack of caster. Bump induced wobbles or occasional wobbles or tire imbalance wobbles or tie rod wobbles or loose components wobble isnt death wobble. Those wobbles are your vehicle needs to be serviced or maintained wobble.

If all you did was pull out of your driveway and hit 3rd gear and it feels like the truck wants to pitch itself into the nearest sidewalk due to instability, thats death wobble.

Death wobble is the shopping cart front wheels flapping left to right as youre racing to get a jug of milk.

 

[mudgudgeon]

I wonder if the term "death wobble" is used properly in this thread.

As far as I understand, death wobble is there every single time on dead flat road accelerating up to speed and can be accelerated through. Induced by lack of caster. Bump induced wobbles or occasional wobbles or tire imbalance wobbles or tie rod wobbles or loose components wobble isnt death wobble. Those wobbles are your vehicle needs to be serviced or maintained wobble.

If all you did was pull out of your driveway and hit 3rd gear and it feels like the truck wants to pitch itself into the nearest sidewalk due to instability, thats death wobble.

Death wobble is the shopping cart front wheels flapping left to right as youre racing to get a jug of milk.

Same same.

Either occur for many of the same reasons.

Lack of caster in itself shouldn't cause death wobble

 

[alia176]

I agree with above, lack of caster isn't usually the cause of DW and neither are bumps. In my case, DW has become a predictable thing every time I drive the 80. I'll try to remember a video of it . Something is amiss in my front suspension, even though all bushings are newish and OEM. I bet my knuckle pre-load has drifted over time. Due to being part time, I don't visit this area much.

 

[jellis]

Hahaha if you can "drive thru" death wobble then I wouldn't call it death wobble!!! Sometimes you get lucky and can accelerate out of the "incipient shimmies" , but proper DW is so intense that your sphincter requires immediate cessation of motion!

Good point on MOUNTING the rim off-center, I'll pay attention to that moving forward! Definitely foreseeable with these massively heavy wheel/tire combos.

The change in late-model lug design coincides with the change to hub-centric rims. The lack of an angular contact surface on late model lugs means that, by definition, the lug cannot center the rim on the wheel without the lug nuts being obnoxiously tight in the rim bore. From an engineering/machining perspective, only one or the other can control the centeredness of the wheel but not both because the design would be over-constrained and couldn't be properly inspected. Functionally one or the other has to float otherwise there could be binding, especially when making hundreds of thousands of units.
Because of that, I always make sure that they use the fingers when balancing my tires on my certainly-crappy aftermarket steelies. Tolerances vary and stack between tire/rim/wheel/balancing machine, sometimes it might all align and work fine without the fingers but there is a 100% probability that sometimes it won't simply because nothing about my vehicle was designed to be mounted that way. I mean, they're mounting it hub-centric to balance (on a non hub-centric rim!) and then I'm mounting it lug-centric on my vehicle......as an engineer with some GD&T experience under my belt, it makes perfect sense that this could lead to repeatably inconsistent results. This is, in fact, a classic example of engineering error in machine design of assemblies--it's really important to conserve datums between different parts in an assembly.

This is an interesting read about some risks of swapping between designs:

What’s the Difference Between Lug-centric and Hub-centric Wheels?

There are two commonly used ways to fasten wheels to a hub: lug-centric and hub-centric. Learn how to tell them apart.

www.machinedesign.com

 

[bjp]

Just a note to everyone that my death wobble does appear to be solved long-term as I've done a number of trips since the main part of this thread without any death wobbles (though I do still shudder at occasional incipient shimmies). I decided I'm never going to have time to make the documentation and code as clear as I'd like to make it easy for other people to use, so here's the existing info on my sensors if anyone is interested:

GitHub - BenjaminPelletier/WobbleTracker: Death wobble measurement and characterization tools

Death wobble measurement and characterization tools - BenjaminPelletier/WobbleTracker

github.com

My life experience has convinced me that I can't trust anyone to do anything right (sometimes including myself, but that's a bunch of stories for other days- this is the short story, remember?). So, I bought a tire balancing machine (and got a tire changing machine in the deal), and a bunch of weights. At over $2k (for a cheap one, I should stress), it was a desperation purchase, but I couldn't think of any other way to get hands-on with a machine to do some testing and figure out exactly what the issue was. Besides, I do like me some tools.

I was actually very seriously looking at some $600-$800 dynamic tire balancers on Craig's list while trying to fix this issue -- your story is helpful and I'll remember it (and honestly, probably buy a balancer) if/when this problem comes up again. Just watching the guy at the tire place do the balancing made your story ring true to me

Bump induced wobbles or occasional wobbles or tire imbalance wobbles or tie rod wobbles or loose components wobble isnt death wobble.

Sigh, false. Here is a video of bump-induced death wobble.

 

[alia176]

Benjamin - your analysis for DW is just SICK. I love it.

 

[jellis]

Wow man, that is truly epic. Your sensor was on the neutral axis for the wheel (on top of the knuckle) yet it STILL experienced an 18g swing (+9 to -9), 11 times a second!!!! That is absolutely terrifying!!!! I guess that's one way to clear your tires...... =P

If you still have shimmies, I'm serious about just upgrading to the Dobinson's adjustable damper. Worked for me. Also, when you tighten it all the way up it sure makes heavy washboards at high speeds a way more relaxed experience.

 

[-Spike-]

Just a note to everyone that my death wobble does appear to be solved long-term as I've done a number of trips since the main part of this thread without any death wobbles (though I do still shudder at occasional incipient shimmies). I decided I'm never going to have time to make the documentation and code as clear as I'd like to make it easy for other people to use, so here's the existing info on my sensors if anyone is interested:

GitHub - BenjaminPelletier/WobbleTracker: Death wobble measurement and characterization tools

Death wobble measurement and characterization tools - BenjaminPelletier/WobbleTracker

github.com

I was actually very seriously looking at some $600-$800 dynamic tire balancers on Craig's list while trying to fix this issue -- your story is helpful and I'll remember it (and honestly, probably buy a balancer) if/when this problem comes up again. Just watching the guy at the tire place do the balancing made your story ring true to me



Sigh, false. Here is a video of bump-induced death wobble.

Nice recap and data, thanks!

 

[CJF]

I doubt my tires automagically become out of round and $hitty . Besides, they're less than 12 mos old and rotated and balanced frequently. Still, I'll rotate them to the rear as a quick check to see if the DW goes away. I'm doubting this will happen but one never knows.

Results?

 

[bjp]

Wow man, that is truly epic. Your sensor was on the neutral axis for the wheel (on top of the knuckle) yet it STILL experienced an 18g swing (+9 to -9), 11 times a second!!!! That is absolutely terrifying!!!! I guess that's one way to clear your tires...... =P

If you still have shimmies, I'm serious about just upgrading to the Dobinson's adjustable damper. Worked for me. Also, when you tighten it all the way up it sure makes heavy washboards at high speeds a way more relaxed experience.

Sounds good -- I'll keep that damper in mind Will probably take a bit of inertia to overcome $475, but we'll see.

Just to be clear, both acceleration (measured with accelerometers) and rotation (measured with gyros) are on that graph -- the two green spikes are multi-G spikes from driving over the two pieces of lumber, but then the wobble is observed most distinctly in the gyros (purple lines) which peak out at somewhere around 200 degrees/s. At 12.8 Hz, that's an amplitude of +/-2.5 degrees. The wobble is visible in the green acceleration line too, but amplitude is "only" +/-2.5 g's vertically give or take (5g swing). But still, it's qualitatively unmistakable