How can I figure out why I have death wobble?

bjp

Joined
Apr 11, 2021
Messages
14
Location
Los Angeles, CA
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:
AM-JKLV3AsFfm_f_Aep2X7zeCWn3oG4E3Uj6J8k4gFzTSp86yaOr5vxQTSbEwRRchurt5SAQ106R7kd5BSI3YmZnXX08ITylryWDto_gtg9QffLKqVvY2SlYRavUIjidNBMNznuW47E73VtCN3zpOFDlGflNjQ=w2614-h1960-no
AM-JKLWJzV7fI1riqlhFv63N5t3tIcehExPze8gRz2hdGgp4k3flGlsPX238QlwBvm3pn3sdkD8uZweR19cAihRmaC1AauEKR1ssd2q4ytYQMoFTHkeKNFrsho3NDVp3BIi9ZoMXnP9PWyc-CwUQHmg_7_z4Gg=w2614-h1960-no
AM-JKLX_NWUZ3X4xIMoJtsIW0m4UzD76wFN2qmzhCvOpPsqmu8zh1aVds2ncGKpXdwUjtMhuGtyHVpVLmyV7XIN0RfGsFwN3vSbwa5Q5lfsvMjQXCWHmbRg_M4TPTSbNQTcoPeQJAXf1NlA8eDwQ8anib9_TGw=w2614-h1960-no
AM-JKLV1UDQuTrv9VWAKorOawU7FmIvASj3OLKrSVSZJCrVJZk1qx-mIcJcAD27STOYL-6bs0RDOxud-CwF85ugeOKuyknlk7hgVFbF8PEQDQ7Fm7vEHxkeErEXafkFDy8KjpT89Hj_gyRmt0T9B5Z2nLCp2nA=w2614-h1960-no
AM-JKLVzqvAdly8XmG6k6WZlyebu-4Mf4S3OMUq710EJ23p7en8czy9OzM9QDlG3oxreue87377VoVbPlOiO2w0mjY7hqWtsBMd7WYAXnQzMrHt_Wm59JAjWveZnjC0aMa_CZP2L-tLm2yiubJMragdQaRTgjg=w2614-h1960-no
AM-JKLXSs77TR621Ruxhqg19VJfm7jJFI14QNHnOfzM38XMxDrnGDBHFCktUdd1OeCcpQlqECBp_6YNlunCWQddMjzIjUJfnEhegMB0lyqPHTupGRlh_m2r1PR215x95C5WMZFJeetwZhnMZnQItkZTeFyVmJQ=w2614-h1960-no
AM-JKLX_zmytYQ20veC3SdlYiQ47tYZKVwXiU1icT1efQwpAalCvQCHfVro13AbeoxJbCYMJEDbpi-BD_jGdLHZBKM8oMDwpubeVk4Z4hi76IBAoA13efwBmCCQ7XCnJ-WgW1JXIeXrP9xY9ttcjt4BYR8UneA=w2614-h1960-no

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?
 
Joined
Dec 17, 2007
Messages
5,243
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Across the pond, and upside down
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:

Anything loose in the front end contributes to death wobbles in my experience. Including wheel bearings in my own experience. I once had death wobbles occurring, then noticed I was also getting heavy feedback/shudder through the brake pedal in some conditions. It turned out both were caused by very loose bearings. The truck still drove nice 99.9% of the time o_O


A little bit of play in any of the joints in the front knuckles or suspension can allow the front wheels to bounce, and rebound side to side, uncontrolled.

I think one thing in isolation is probably not gonna do it, more likely a combination of factors.

I think it only takes a small amount of play, theft add big tyres with tall sidewalls, and the play is amplified
 

bjp

Joined
Apr 11, 2021
Messages
14
Location
Los Angeles, CA
Thanks for all the feedback; here are my notes for possible causes so far:
  1. No steering damper
  2. Alignment (@gnob)
  3. Caster too low (@gnob, @gummycarbs, @toyotaboy80, @baldilocks)
  4. Unbalanced wheels/tires (@jpoole, @MrMacdugal, @flyingmonkey)
  5. Panhard bushings (@AussieHJCruza, @Squeegee, @mudgudgeon, @alia176)
  6. Shocks (@baldilocks)
  7. Old tires (@baldilocks)
  8. Wheel bearing preload (@mudgudgeon)
  9. Toe-in too small (@baldilocks)
  10. Loose cone washers on knuckles (@alia176)
There are a number of things for me to try, but I wanted some better way to evaluate whether a change was making things better or worse since I couldn't produce wobble reliably. So, I stuck accelerometer/gyros on both knuckles and both axle ends:
AM-JKLUEFiToB70W-U9cbNCKFqRiPQXz10Ll0r8QkOUTUkQqrTkPI4nHvQ1I3Gf1AoDOkF11hXPOA3m0QnmZn-TAXhWwWFJqjaHOivlsxRtHNy3oLLWkw2u4jx_dFDBIDeP0i1UqPW_bh40U7Ul4I02yd7zJdg=w2614-h1960-no
AM-JKLUZWOLoTDohZIyRszGQEtCD9tgiD2LrNR1tkildf3WPUKLw5R9H-bwiDRgfrgBvG0_xL23x-Ps-rlZr3lRgAlV81zDqFQboGE0Nu-GNP5D7UhvBI8uHZDLO8-f8e0i-V7joYwivmZoIHOm65N0r7PZi1g=w2614-h1960-no


Then, following @flyingmonkey's reference pothole comment, I managed to find a pothole that seems to be bad for death wobble and then recorded a wobble with the sensors. It looks like there are two bumps in a row that happen to be spaced very closely to the system's resonant frequency when I'm driving 40mph, and that triggers wobble which is primarily knuckle rotation about the vertical axis. In all the diagrams below, P is passenger, D is driver, ax is acceleration to the right, ay is acceleration forward, az is acceleration upward, rx is positive rotation about the x axis, ry is positive rotation about the y axis, and rz is positive rotation about the z axis.
AM-JKLULuZNUVXjB6xf5qgwg-8QK3v4BWcaI9w5eZ2QiiWe9eT8uTHzUEoIbxUMeheKOF40SEeOf9K63mwTfsn-CwuylQTw-mWL0ntkEn2oMyNqGFEtPKOigxc-7-QAh9yT9Xd_bzD37HDnQkan0b3wtuf-cCg=w1362-h692-no


I noticed a few interesting things. First, the wobble is a rotation of the knuckle about the vertical axis; the other two rotation axes don't move much compared to that vertical rotation:
AM-JKLVkNAsB56PD21o7vwFqAbccX0WVGUB4hNWs-5PNE-ZKpiOiuvfOEl4pGlhtnu_IjwTROeilHcUJHU4kmzBdfAwzU4BnsX54zT9kJ9U_Zo_EztfSJtBMfTWk9yOeegBzOB-9wiolwruFcsz99bTknc7RQg=w1365-h698-no


Second, both knuckles wobble together:
AM-JKLW7EO-iLB5s-PynPyHnVEmgyQ4B2_y6at_otfuizBKmdSj_8WHhJ0e0N-7ICUhp2Fd5ZueQuaGCqSfvxogU0xvhmaFlQfDeVHqxxE9RabxS8QYmNfLtstnSt6Vc5cyJDd5XOn9m8WuVj_46SZYdNfHcig=w1371-h701-no


Third, it's just the knuckles wobbling; not the axle:
AM-JKLUW-RNQIgAPEvskmKlHWs7dWJpWxYQxP2fnIMJ53B1PrFbTgif6nWUrjtF8J1N7RMoN4VEv7hd-v2gQ3Sm46Ta4kh1WLdJHRNop8W0hAghuqPJgQCTETLplkECwVsLaexlxB_aVa-P0CxJQzmHkHMf7iA=w1366-h703-no


I hope to figure out more about the nature of the wobble later (e.g., how does speed change the characteristics, how repeatable is it, etc), but I feel like this informs some of the possibilities above; let me know if you think this is right:
  • The steering damper now seems most likely now since it damps exactly the knuckle rotational movement I'm seeing
    • Are there such things as cornstarch dampers? Like, dampers that are extremely resistant to fast movements, but much less to slow movements (in a non-linear way), in the same way that cornstarch and water behaves.
  • Caster seems likely as well, but I'm going to shelve this one for now since the only thing I can do is buy another set of $1k arms
  • Shocks and panhard bushings seem less likely since those would wobble the axle as well as the knuckles
What do you think is flexing to produce the rotational movement of the knuckles? The steering box was just rebuilt so it shouldn't have much play. The drag link is heavy duty. Could I reduce a wobble by holding the steering wheel in place more forcefully? Other thoughts?
 

alia176

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steering damper is not the cause of a DW, I don't think. In fact, we should be able to drive w/o a steering damper if everything up front is nice and tight.

Interesting data, love the graphs. What sensor did you end up using and what app? I love this geeky s***!

This guy did a decent job of DW
 
Last edited:
Joined
Apr 14, 2016
Messages
1,253
Location
Oregon
Are there such things as cornstarch dampers? Like, dampers that are extremely resistant to fast movements, but much less to slow movements
As I understand it, that's exactly how steering dampers work.

I think you should find a way to get your caster checked. Put on stock wheels if you have to. Also, examine the wheel bearings and reset them. Don't try to logic your way out of checking what is likely the second most common cause of steering/handling issues on these vehicles.
 
Joined
Feb 16, 2012
Messages
275
As I understand it, that's exactly how steering dampers work.

I think you should find a way to get your caster checked. Put on stock wheels if you have to. Also, examine the wheel bearings and reset them. Don't try to logic your way out of checking what is likely the second most common cause of steering/handling issues on these vehicles.
Completely agree, start with the basic thing then move to more complicated testing if those don’t work.
 
Joined
Apr 17, 2018
Messages
1,036
Location
Roanoke, VA
Thanks for all the feedback; here are my notes for possible causes so far:
  1. No steering damper
  2. Alignment (@gnob)
  3. Caster too low (@gnob, @gummycarbs, @toyotaboy80, @baldilocks)
  4. Unbalanced wheels/tires (@jpoole, @MrMacdugal, @flyingmonkey)
  5. Panhard bushings (@AussieHJCruza, @Squeegee, @mudgudgeon, @alia176)
  6. Shocks (@baldilocks)
  7. Old tires (@baldilocks)
  8. Wheel bearing preload (@mudgudgeon)
  9. Toe-in too small (@baldilocks)
  10. Loose cone washers on knuckles (@alia176)
There are a number of things for me to try, but I wanted some better way to evaluate whether a change was making things better or worse since I couldn't produce wobble reliably. So, I stuck accelerometer/gyros on both knuckles and both axle ends:
AM-JKLUEFiToB70W-U9cbNCKFqRiPQXz10Ll0r8QkOUTUkQqrTkPI4nHvQ1I3Gf1AoDOkF11hXPOA3m0QnmZn-TAXhWwWFJqjaHOivlsxRtHNy3oLLWkw2u4jx_dFDBIDeP0i1UqPW_bh40U7Ul4I02yd7zJdg=w2614-h1960-no
AM-JKLUZWOLoTDohZIyRszGQEtCD9tgiD2LrNR1tkildf3WPUKLw5R9H-bwiDRgfrgBvG0_xL23x-Ps-rlZr3lRgAlV81zDqFQboGE0Nu-GNP5D7UhvBI8uHZDLO8-f8e0i-V7joYwivmZoIHOm65N0r7PZi1g=w2614-h1960-no


Then, following @flyingmonkey's reference pothole comment, I managed to find a pothole that seems to be bad for death wobble and then recorded a wobble with the sensors. It looks like there are two bumps in a row that happen to be spaced very closely to the system's resonant frequency when I'm driving 40mph, and that triggers wobble which is primarily knuckle rotation about the vertical axis. In all the diagrams below, P is passenger, D is driver, ax is acceleration to the right, ay is acceleration forward, az is acceleration upward, rx is positive rotation about the x axis, ry is positive rotation about the y axis, and rz is positive rotation about the z axis.
AM-JKLULuZNUVXjB6xf5qgwg-8QK3v4BWcaI9w5eZ2QiiWe9eT8uTHzUEoIbxUMeheKOF40SEeOf9K63mwTfsn-CwuylQTw-mWL0ntkEn2oMyNqGFEtPKOigxc-7-QAh9yT9Xd_bzD37HDnQkan0b3wtuf-cCg=w1362-h692-no


I noticed a few interesting things. First, the wobble is a rotation of the knuckle about the vertical axis; the other two rotation axes don't move much compared to that vertical rotation:
AM-JKLVkNAsB56PD21o7vwFqAbccX0WVGUB4hNWs-5PNE-ZKpiOiuvfOEl4pGlhtnu_IjwTROeilHcUJHU4kmzBdfAwzU4BnsX54zT9kJ9U_Zo_EztfSJtBMfTWk9yOeegBzOB-9wiolwruFcsz99bTknc7RQg=w1365-h698-no


Second, both knuckles wobble together:
AM-JKLW7EO-iLB5s-PynPyHnVEmgyQ4B2_y6at_otfuizBKmdSj_8WHhJ0e0N-7ICUhp2Fd5ZueQuaGCqSfvxogU0xvhmaFlQfDeVHqxxE9RabxS8QYmNfLtstnSt6Vc5cyJDd5XOn9m8WuVj_46SZYdNfHcig=w1371-h701-no


Third, it's just the knuckles wobbling; not the axle:
AM-JKLUW-RNQIgAPEvskmKlHWs7dWJpWxYQxP2fnIMJ53B1PrFbTgif6nWUrjtF8J1N7RMoN4VEv7hd-v2gQ3Sm46Ta4kh1WLdJHRNop8W0hAghuqPJgQCTETLplkECwVsLaexlxB_aVa-P0CxJQzmHkHMf7iA=w1366-h703-no


I hope to figure out more about the nature of the wobble later (e.g., how does speed change the characteristics, how repeatable is it, etc), but I feel like this informs some of the possibilities above; let me know if you think this is right:
  • The steering damper now seems most likely now since it damps exactly the knuckle rotational movement I'm seeing
    • Are there such things as cornstarch dampers? Like, dampers that are extremely resistant to fast movements, but much less to slow movements (in a non-linear way), in the same way that cornstarch and water behaves.
  • Caster seems likely as well, but I'm going to shelve this one for now since the only thing I can do is buy another set of $1k arms
  • Shocks and panhard bushings seem less likely since those would wobble the axle as well as the knuckles
What do you think is flexing to produce the rotational movement of the knuckles? The steering box was just rebuilt so it shouldn't have much play. The drag link is heavy duty. Could I reduce a wobble by holding the steering wheel in place more forcefully? Other thoughts?
I missed whether you replaced panhard bushings or not - but if you haven't that's where I would look given the "rotational" wobble you have. That's what mine was doing and if you think about it, the panhard is simply a two-point connection between the frame and axle - so any lateral movement of the axle (which would thereby force knuckle rotation unless the tires break traction) has to influence those bushings. Loose bushings = more play = violent wobble when triggered. Mine was triggered by old tires but allowed to happen by worn bushings.
 
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Could I reduce a wobble by holding the steering wheel in place more forcefully? Other thoughts?

No, because the wobble is in the system joints after the steering box.

FWIW, I've removed dampers on two of my cruisers and never replaced it and never missed them.
It won't stop wobbles which is a high frequency oscillation of relatively small movements as shown by your charts. Steering damper is of most value to big bumps IMO


In regards to your list above, there a number of things there to investigate that will take a small amount of time, and cost virtually nothing to check over before you start throwing cash at stuff.

Interesting to have your data. It means you probably should focus on the things that allow the knuckles to oscillate

Eg
Check panhard bushes (remove panhard rod for a thorough check over)
Check knuckle stud nuts
Check for play in tierod ends (not in your list)

Wheel bearings are probably lower priority.

Lack of caster means death wobble is more likely to occur, but I think its not the main cause.
Caster loads the system so the knuckles always have tension on them. Zero caster allows them to oscillate more easily because the no load one way or the other. Same with toe in/out
 
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Just want to throw this out there... I'd been fighting a death wobble for two years or more. I replaced bushings, balanced tires, replaced dampener, new wheel bearings, blah, blah, blah. None of this fixed the problem.

Two months ago I did a brake overhaul and replaced the master cylinder, calipers, rotors, and pads. All OEM parts... The death wobble disappeared immediately! I don't understand it, but the wobble is gone. Good luck!
 
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Location
Roanoke, VA
Just want to throw this out there... I'd been fighting a death wobble for two years or more. I replaced bushings, balanced tires, replaced dampener, new wheel bearings, blah, blah, blah. None of this fixed the problem.

Two months ago I did a brake overhaul and replaced the master cylinder, calipers, rotors, and pads. All OEM parts... The death wobble disappeared immediately! I don't understand it, but the wobble is gone. Good luck!
Rotors/pads/sticky pistons might have been causing uneven pressure application leading to a shudder... good data point, though. That's interesting.
 

roadstr6

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Look at the panhard bushings as well as the fitment of the bolts through the metal sleeves of the panhard bushings. The bolt should be a snug fit through those bushings. Any slop there will cause problems. I've seen some aftermarket adjustable panhard bars that had bushings that were too large for the factory panhard bolts. Tightening the sh@t out of the bolts will not fix this. You need the bolts to fit tight in the bushings.
 

alia176

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Look at the panhard bushings as well as the fitment of the bolts through the metal sleeves of the panhard bushings. The bolt should be a snug fit through those bushings. Any slop there will cause problems. I've seen some aftermarket adjustable panhard bars that had bushings that were too large for the factory panhard bolts. Tightening the sh@t out of the bolts will not fix this. You need the bolts to fit tight in the bushings.

Panhard rod bushings have been mentioned over and over so let's see their condition!
 

bjp

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A shopping carts front wheels have death wobble. The cause is because they dont have natural stability in the geometry.

Agreed and I will check the caster when able (arranged to borrow wheels from a buddy on Saturday). However, I was expecting that I already fixed caster so I'm going to be bummed if the issue is actually caster. I'll also be surprised because there wasn't any wobble with stock arms and I now have the DeltaVS 4" arms which should only improve the situation from stock with regard to caster (right? but see below).

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.

The idea when I got the arms was that I could choose 4" or 6" (5" weren't available at that time), my measured 5" lift was when unloaded, and I planned to use the truck mainly with load (thus reducing the lift and increasing caster). I thought people routinely have 2" lifts with no correction and that's fine, so a 5" lift on 4" arms should be fine (only a ~1" lift without correction). Your estimate of 2 degrees per inch of lift struck me as way too high, but Dave puts the number at 3-3.5 degrees per 2 inches of lift which is pretty close. The surprising result there to me is that you're right: assuming the 4" arms put me at exactly the right caster with a 4" lift, then a 5" lift should subtract 1.5-1.75 degrees of caster, which puts me 0.5-0.75 degrees out of the range specified in the FSM (which is +/- 1 degree).

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.

I measured the front diff companion flange with driveshaft off a while back (but after the DeltaVS arms) and it is 2.6 degrees above horizontal. That means...I have more caster than you do?? That doesn't seem to make any sense... I thought I was pretty careful about leveling for this measurement (used a laser level to put each pair of wheels at the same height as each other, to within about 1/4-1/2" or so), but I don't see how 2.6 degrees makes sense against your 5 degrees with 6" arms versus my 4" arms. FWIW, I measured the transfer case flange at 6.8 degrees downward.

I took the left picture below before installing DeltaVS 4" arms and the right picture just after installing them. The truck is on a fairly level surface, but it could be as much as ~1.5 degrees off -- so these may only help estimating caster before I measure it on Saturday.
AM-JKLXSU-7GQH8IPPnmhmQu51VEmJlThiLvG44jOJKBlvBcLM6NM-hfeabcS8fculQX0bMMi7LEfPodLyNfBxVZgdpDg7x3exrKFwXrFgJ3lrFj-JItrfhYQbolyggjtbn0x8Ugz-TWYDMTqOJuRbp0jRBbzg=w1734-h1301-no
AM-JKLXe5enF-CS1suq3JY9dNRk3hUXcuIzZ_sxkgvlQPuvQA7DXJmER1kYSNBlQ9mm90X5YVMUMHEL0zQItjcMpqn9_gJ0nbdFKj75_MqIVuRTOkQeCcfxJqXYBT9hzT7yL02WK1C7BmCEMrH5iwndu-nlurA=w1734-h1301-no


Check for play in tierod ends (not in your list)

Just replaced with brand new Trail Gear heavy duty ends (along with their heavy duty rod) as part of my primary attempt to fix (in long OP).

Lack of caster means death wobble is more likely to occur, but I think its not the main cause.
Caster loads the system so the knuckles always have tension on them. Zero caster allows them to oscillate more easily because the no load one way or the other. Same with toe in/out

Now that's interesting. Surely I had negative caster before and I just added 7.3 degrees of caster. Since FSM targets +2 degrees and I'm 1" over the ideal lift for my arms, that probably puts me at a fraction of a degree over 0. Are oscillations more likely at -7 degrees or 0 degrees? If 0, maybe the caster-correcting arms are actually the cause of the issue; the timing would fit reasonably well. I previously thought 0 degrees of caster was better (more stable) than -7 degrees.

Panhard rod bushings have been mentioned over and over so let's see their condition!

Pictures in #6? Happy to take more.

Look at the panhard bushings as well as the fitment of the bolts through the metal sleeves of the panhard bushings. The bolt should be a snug fit through those bushings. Any slop there will cause problems. I've seen some aftermarket adjustable panhard bars that had bushings that were too large for the factory panhard bolts. Tightening the sh@t out of the bolts will not fix this. You need the bolts to fit tight in the bushings.

Makes sense; will put on the list to check.

[...] the wobble is in the system joints after the steering box.

Are we sure about that? With a peak rotational speed of 150 degrees/sec at 6Hz (read from graphs), that implies a 4.0 degree rotation of the knuckles each direction (I think). I don't know what LC's steering ratio is, but if we assume 15:1, that implies the steering wheel bouncing 60 degrees one way and the other (assuming wobble is transmitted fully back to the wheel). The steering wheel was not rotating that much, so at least the wobble is after the steering wheel. So I assume you're right, but out of curiosity, how do you know the wobble isn't (at least partially) in the steering box? Something inflexible has to be flexing, so why not the box also?

FWIW, I've removed dampers on two of my cruisers and never replaced it and never missed them.
It won't stop wobbles which is a high frequency oscillation of relatively small movements as shown by your charts. Steering damper is of most value to big bumps IMO

That lines up with my current understanding and is why I didn't immediately install the steering damper. In software at least (I don't have nearly as much/almost any experience with Land Cruisers/cars), it's much better to have a reliably reproducible bug than band-aiding the problem so the issue is harder to detect but without resolving the root cause.

In regards to your list above, there a number of things there to investigate that will take a small amount of time, and cost virtually nothing to check over before you start throwing cash at stuff.

Before I *start* throwing cash at the problem you say? :p Agreed, I'm hoping to do these cheap diagnostics before continuing to throw cash at the problem.

I missed whether you replaced panhard bushings or not - but if you haven't that's where I would look given the "rotational" wobble you have. That's what mine was doing and if you think about it, the panhard is simply a two-point connection between the frame and axle - so any lateral movement of the axle (which would thereby force knuckle rotation unless the tires break traction) has to influence those bushings. Loose bushings = more play = violent wobble when triggered. Mine was triggered by old tires but allowed to happen by worn bushings.

I'm not questioning that loose panhard bushings can cause rotation in the knuckles, but I would like to understand/picture the mechanism and don't/can't currently. You're saying if I push laterally on my axle, the will force the tires to rotate (assuming they don't break traction), and a loose panhard rod will cause increased lateral forces?

Separately, I have made some progress on reliably reproducing wobble; I can trigger it every time the same way if I drive over two 2x6's spaced 17' apart at 35 mph:
AM-JKLXTqy9ulCkL5x4wF5QdcrZ-3k7ar_qL2Bho5U40-nit6LAC5Uhm4tTmOuL6Cv8OIQxq7AisUpJl6V4ybtudDsYs0O1kHGvyD33tdeNuzFBUULz8wOT0eqMrUeLYG2l3V6z9TyTicVljEn10kh44_AG4Yw=w1734-h1301-no
 
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I'm saying if something causes a lateral force on the axle - turning at speed, for example - the panhard sees either tension or compression depending on the direction of that force. Either one will be translated through the bushings because that is the point of connection to the axle housing. The comment I made about assuming the tires have traction was to point out that the knuckles are turning because the tires contact with the ground is not shifting (laterally) but the axle is (hence the shimmy). All of these pieces are individual components of a system. That sounds obvious but if you remember to think of them that way, it will make more sense. The reason people keep asking you about the panhard bushings is because the data you posted indicates that something is causing the knuckles to oscillate about the trunion bearings (like they normally do when you turn the steering wheel). This means your front tires are whipping back of forth about their normal turning axis as you go down the road. This movement is causing the while front end to move. That type of movement is only possible if something is loose or disconnected entirely. The panhard exists to prevent this type of motion so if it's still occurring, which you have proven, then everything you've said thus far points to the panhard not doing its job. Now, WHY it isn't doing its job is anybody's guess - but the overwhelming majority of us have found via experience that the bushings can be a culprit. Hence, why it has been suggested about 7 times now. That's not meant to be rude, just explaining why it keeps getting repeated.
 
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Are oscillations more likely at -7 degrees or 0 degrees?
More likely at zero degrees. My understanding is that either positive or negative caster is stable, but negative caster will wander more than positive.

What steering damper are you running? I could swear that I saw someone (@cruiserdan ?) mention replacing an OME damper with a stock Tokico to eliminate very small oscillations.
 

baldilocks

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I’ll take my angle measurements again out of my own curiosity because it does seem strange that your pinion flange is up only half that of mine unless your rig is not as tall as I’m assuming it is.

You labeled before and after pics as left and right which isn’t easily discernible given the fact that they post one below the other and the pics themselves look identical other than the number on the tool. We’re both pics of the same knuckle?

Your front transfer case flange should be about 2* up and the rear about 2* down. Your measurement of 6.8* up is worth looking into.
 

bjp

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I'm saying if something causes a lateral force on the axle - turning at speed, for example - the panhard sees either tension or compression depending on the direction of that force. Either one will be translated through the bushings because that is the point of connection to the axle housing. The comment I made about assuming the tires have traction was to point out that the knuckles are turning because the tires contact with the ground is not shifting (laterally) but the axle is (hence the shimmy). All of these pieces are individual components of a system. That sounds obvious but if you remember to think of them that way, it will make more sense. The reason people keep asking you about the panhard bushings is because the data you posted indicates that something is causing the knuckles to oscillate about the trunion bearings (like they normally do when you turn the steering wheel). This means your front tires are whipping back of forth about their normal turning axis as you go down the road. This movement is causing the while front end to move. That type of movement is only possible if something is loose or disconnected entirely. The panhard exists to prevent this type of motion so if it's still occurring, which you have proven, then everything you've said thus far points to the panhard not doing its job. Now, WHY it isn't doing its job is anybody's guess - but the overwhelming majority of us have found via experience that the bushings can be a culprit. Hence, why it has been suggested about 7 times now. That's not meant to be rude, just explaining why it keeps getting repeated.

Thanks for your patience; I have very little experience with LCs & cars generally so this kind of explanation is definitely appreciated. It's still a challenge because there's conflicting info, so I (with less knowledge and experience than all the other commenters) have to figure out which thing I think is most likely even though I'm probably the least qualified person here to do that :) In this case, I have a buddy who suggests the panhard has nothing to do with death wobble and I've read a couple comments to that effect in some Facebook groups which is why I was asking for more explanation, but I'm convinced by yours (and others') explanation.

So, I'll jack the front up by the frame, remove both front wheels, remove the two bolts, remove the panhard rod, and take some pictures?

Does anyone recognize which panhard rod this is so I can order new bushings?
AM-JKLWhKm4Q6nccN3N0OkfmV8puMcmdO4bH07OKZ5W8ZRg9T5QgGeP_SMa_PRxN7azZrPYXnbBVwPfr370Yd3b_Z-p3gAJeT6PXIC0mqf-Pn7e5xznI3WfvqqI85TMMMI1GgUlqZNnhnaYe4igSE_vmQBgUuA=w2614-h1960-no



Interesting data, love the graphs. What sensor did you end up using and what app? I love this geeky s***!

The sensors are old MPU6050 accelerometer/gyros. They're connected to an ESP32 Arduino which is just plugged into a laptop (via USB) that records the data. I wrote the Arduino firmware, Windows logger, and Python-based analyzer/plotter. I'd be happy to share if someone was interested, but I assume no one else actually wants to do this. Marginal parts cost for someone else would probably be around $50, but I already had everything lying around from past projects.
 

rdcnj

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Can you share the sensors and setup you used to get those graph readings?

The sensors are old MPU6050 accelerometer/gyros. They're connected to an ESP32 Arduino which is just plugged into a laptop (via USB) that records the data. I wrote the Arduino firmware, Windows logger, and Python-based analyzer/plotter. I'd be happy to share if someone was interested, but I assume no one else actually wants to do this. Marginal parts cost for someone else would probably be around $50, but I already had everything lying around from past projects.


I would be interested in your setup and would gladly pay for the details on the setup. You responded as I wrote the comment above.
 

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