How can I figure out why I have death wobble?

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bjp

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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:
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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?
 
Delta VS

Delta VS

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A. Will trade you stuff for those wheels when it's time for them to go

B. Have you grabbed the top of the tire when all four are on the ground and pushed/pulled hard (when standing next to vehicle) to see if you can feel movement wheel bearings/knuckle bearings? Easy/quick way to see if things are loose there (sounds unlikely with all the stuff you've done though). would help if I read every word...
 
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gummycarbs

gummycarbs

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Grab the FSM, climb under there, and check the torque on every fastener related to suspension and steering. Inspect the rubber bushings while you're there.

Get your alignment professionally checked to see what your caster is.

Which Tom Woods drive shaft did you get, and is your pinion angle correct for it?
 
jpoole

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I only skimmed but didn't see mention of you testing by moving tires, in this case moving fronts to back, to see what impact that has. While you may have insufficient caster, looseness in the system, etc. that are important factors you may also have out of round/balance tires/wheels that are causing the initiation of the vibes/wobble. If you haven't tried it it can also be an easy and free way to learn more before you try other options.
 
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bjp

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Find a real alignment shop.
Beadlocks have zero to do with alignment. :rolleyes:
My experience with DW is, its a caster or tire issue.

Real alignment shop (for 4x4s) wants $140 to adjust the one axis (toe) that can be adjusted on the 80s; do you think there might be something wrong with my method (pictured)? The standard fiducial device most alignment shops use can't be attached to the beadlock ring. I've been to multiple shops and they say the same thing.

Grab the FSM, climb under there, and check the torque on every fastener related to suspension and steering. Inspect the rubber bushings while you're there.

Get your alignment professionally checked to see what your caster is.

Which Tom Woods drive shaft did you get, and is your pinion angle correct for it?

Rubber bushings on radius arms are brand new, panhard bushings seem maybe ok? (I don't have enough experience to judge; see below) Radius arm fasteners are torqued to spec. Lug nuts torqued to spec under partial load; will retorque with wheels completely off the ground. Panhard jam nut torqued as much as I can reasonably torque it. Knuckle nuts seem torqued to spec per original message, drag link and tie rod jam nuts torqued appropriately per original message. Are there any other fasteners that could affect death wobble?
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The only place that says they can measure my caster wants $140 to do it (they don't measure without an alignment). The standard fiducial most shops use won't attach to beadlock rings apparently (multiple shops have said that). So, would love to measure caster, haven't been able to yet. But, I'd be surprised if it's very far off since the DeltaVS arms.

Got the standard Toyota double cardan driveshaft from Tom Woods; can dig up the measurements I provided if useful. Pinion angle should be reasonably close; see picture for qualitative idea.
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B

bjp

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I only skimmed but didn't see mention of you testing by moving tires, in this case moving fronts to back, to see what impact that has. While you may have insufficient caster, looseness in the system, etc. that are important factors you may also have out of round/balance tires/wheels that are causing the initiation of the vibes/wobble. If you haven't tried it it can also be an easy and free way to learn more before you try other options.

Makes sense; will try (haven't tried that yet).
 
flyingmonkey

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I also spent a looong time chasing death wobble on my rig. Very similar setup; lifted, same tire and size, etc... Did a lot of the same things you have done; rod ends, knuckle rebuilds, alignments, bushings, etc.

What it came/comes down to for me is those tires become unbalanced pretty quickly. Immediately after they are balanced, no wobble. Drive around a few weeks (sometimes months since it's not my daily) and wobble will start to creep in, it gets progressively worse over time. If I let it go too long before rebalancing the wobble can feel like the vehicle is going to fall apart. There are certain potholes along some of my common routes that I use as "test" holes to see if I need to take it in for rebalancing.

I'm switching tire/wheel combo soon, so hopefully that will help me out. But for now, I just hit one of my test potholes every now and then to see what's up.
 
T

toyotaboy80

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Draw a line vertically through the king pin centers. That determines your caster angle. You NEED positive caster to maintain knuckle stability. Positive is when the angle is raked backwards. 4° should be plenty in a static position.
 
A

aktundra

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I think most will agree, that there is no single source of DW. I have 44” tires mounted on 15” wheels. So there is a certain amount of play simply in the sidewalls.

I’ve replaced all the wear parts associated with the front end, keep everything torqued to spec, spin balanced tires with lead (rather than beads), I’ve even shaved the tires. I think I’ve done all that can be done. After I drive a few miles and get the tires warmed up, I’ve got not problems. But on cold tires I will almost always get DW, decelerating, through 40-45 mph. Outside this speed range, accelerating, warm tires, no problem.

I realize my tires, are extreme & none of this is necessarily applicable to more practical modifications. However I can attest that there is no single cause of DW. Just work through components one at a time, with some consolation that most of this work involves wear items and will have to be done sooner or later anyway.
 
baldilocks

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^^^^^ This….. I’ve had 80’s lifted from 2” up to nearly 6”. I can tell you that with 5” lift and a pinion angle that’s perfect for a DC shaft you are castor angle deficient. The 4” delta arms on a 5” lift only serve to prove my point. Currently mine sits at about 5”-5.5” lift. With the old 4” lift castor plates my DC shaft was aligned perfectly but my castor angle was .5 and .8 positive. After installing delta 6” arms my castor is 5* plus (I like it that way) but my pinion is down to low to run the dc shaft perfectly smooth above 40-45mph (doesn’t matter as my rig is part time). Extra castor angle is desirable with taller lifts and larger tires. Put a steel ruler and a digital angle finder across the tops of your upper trunnion cap bolts taking into consideration the angle of the floor the rig is parked on to get an idea of what your castor angle is.

I corrected DW on my dodge 3/4 ton 4x4 by replacing the junky shocks Les Schwab installed years ago with Bilstein 5100’s. Almost ten years and 125k miles later no episodes of death wabble.

A year ago I drove through a pothole with my cruiser at about 35 mph and the front end went into convulsions out of the blue for the first time. Come to find out the front right shock was toast. Was a bit of a surprise bc the shocks were only 3 years old.

How old are the shocks? What is the date of manufacture on the tire side wall?
 
mudgudgeon

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You haven't said you opened hubs and checked wheel bearings.

I'd retorque bearings, preload bearings to 30lb on the inner nut, rotate hub a few times, recheck torque before adding locking tab washer and outer lock nut.
Even if you think a PO, or mechanic has done them recently, I would 100% say check them. Costs nothing, and if they aren't set right, the can have play in very short order. As in weeks!
What you describe happening on a slight bend suggests bearings might not be 100% dialed in.

Also, your panhard rod looks to have aftermarket poly bushes. Poly bushes can be very short lived.
Change them out for OEM press in rubber bushings.

I also think your caster could be marginal. 5" lift with arms for 4" lift means your caster is gonna be nearly 2⁰ lower than ideal straight up.

Agree with comments above. It won't be one single thing that causes wobbles, more typically a combo of a few things being out of spec, or having some play.
 
T

toyotaboy80

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Does positive rake level the third member with the ground or point it more upward, toward the truck?

From stock, more positive caster will tilt the pinion flange toward the ground. Likewise, more upward pinion angle will decrease positive caster.

On an 80 series axle I am not sure what the stock relationship is between factory pinion and factory caster angle is.

Roughly speaking if one knew the stock flange angle and stock caster angle they could extrapolate one or the other.

A 1985 truck axle with leaf springs has a 4° pinion flange towards the floorboard and resuts in a 4 degree positive caster angle.
 
mudgudgeon

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On an 80 series axle I am not sure what the stock relationship is between factory pinion and factory caster angle is.

Roughly speaking if one knew the stock flange angle and stock caster angle they could extrapolate one or the other.

In stock configuration, the 80 pinion points up toward the transfer case.

You are correct the pinion flange angle can be used to determine the approximate caster angle. Only problem there is the driveshaft is in the way.

There can be as much a 2⁰ variation in caster from the factory, so measuring from the pinion flange is gonna give you an approximate caster
 
baldilocks

baldilocks

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Does positive rake level the third member with the ground or point it more upward, toward the truck?
I took angle measurements with a digital angle finder. These are “close” numbers, close enough for the girls we go with anyway.

Across the upper trunnion cap bolts I got 5* left and 5.5* right. The companion flange is 85* or 95* depending on which way apply the angle finder so the pinion companion flange is 5* up from being 90* to the floor. This is with 5” to 5.5” of front lift and Delta 6” arms.

Yes, rotating the axle housing back so the pinion is closer to the floor increases castor angle. Also from these measurements we learn that the there is approximately 10* separating the knuckles from the companion flange using an imaginary line drawn down through both trunnion bearings.

The photos show my lift height for comparison and driveline to pinion angle for comparison purposes and shows why I said a few days ago that the OP’s rig probably has low castor numbers for the lift height. More castor and toe in will help keep the beast under control.

0CC69AB6 B755 41AE AAF2 AC0E94552E01
82094108 416E 487F 99AE 5D6819BEBC1E
 
alia176

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Another vote for checking the panhard rod bushings. Remove the panhard rod, stick it on a vice. If you don't have a vice, stand on it, then use a long screwdriver or a long rod through the center hole, yank it this way and that way to see if the bushing cracks open up. It's an easy fix to replace, then see what happens. Your radius arm bushings are new so you're GTG there.

In my experience, loose hubs or bearings don't cause DW by and large. DW causes the steering wheel to violently rotate back N forth, while your front wheels are doing the violent side to side dance. It's scary chit, no lie. Loose wheel bearings will cause your steering to be a little wondering side to side while driving and maybe some uneven tire wear. I've been guilty of not checking my WB tightness and was able to easily move the wheel side to side/up and down.

Out of balanced tires are just annoying at specific speeds and I've been dealing with this during the entire 80 ownership. Sometimes they get it right, other times, it's crappily balanced :bang:. Never have I had DW due to out of balanced or out of round tires. Ever.

Bad caster will cause your steering on the road to be twitchy, if too low of a number, like 1deg or 1.5deg, etc.

Bad toe # will cause your wheels to grab ruts easier and pull to one side or the other.

Loose knuckles, hmm, that's an interesting one. Would loose cone washers on the bottom of the knuckles contribute to DW? 🤔

Good luck amigo and a great post detailing the problem and solutions tried. :clap:
 
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