Death wobble may be the death of me.. suggestions. (1 Viewer)

[Nay]

Sometimes pictures say a thousand words also.. so here is a rough idea of where the truck sits height wise. And give me a break on the cleanliness.. poor gal hasn't seen a trail in longer than I'd like to admit. Problem is.. when you live in Memphis you have to drive minimum 4 hours to get to any respectable trail.. and until this issue is resolved that won't be happening..

Front
View attachment 1305803

One other thing. That is a ton of front lift. I am on 37's and my ground to fender is about 40" (I don't have flares, so maybe 1/4" variance there based I how I estimated for flares).

The first thing I would do is drop the front 1.5-2" - it's way higher than the rear. All of your angles will improve and it would probably line up that front shaft. Having a lot of angle on steering and panhard can also contribute to those steering wobbles. I had thought that pic was the rear, but looking again I realized it is the front.

That's an unbalanced suspension that is very tall exactly where front end geometry issues come into play, and I can't see a reason to spend the money to try to keep it. That pic is worth a thousand words - it shows a primary problem very clearly.

Here are my pics for comparison, front first and then rear and full.

 

[White Stripe]

Agreed that those initial gravity protractor measurements suggest driveline angle issues.

Up front, a 3 degree variance in pinion to driveshaft angle means a 3 degree operating angle on that u-joint. It has to be very close to zero (the pinion and driveshaft are at the same angle) for that DC shaft. That driveshaft should be growling for sure at those higher highway RPM (68 mph and up). I would talk to Slee with the thought of using his caster correction for the 6" kit. Basic correction here was not enough (and shouldn't have been for those springs).

For the rear, don't worry about measuring the driveshaft or pinion angles. Measure the actual u-joint angle by making sure one of the caps is pointed straight down and then use a socket to extend the cap for a flat surface for your gravity protractor. The angles for the t-case and axle side u-joints should be nearly equal (or equal and opposite such as 3 degrees and -3 degrees). Even in phase, once you are getting up to 5 degrees or so those joints may be unhappy. Think about that entire assembly running in an elliptical arc at higher RPM. For a lot of highway miles, I would convert the rear to a DC shaft with upper adjustable control arms to set that axle side u-joint angle to 0 / -1 degrees.

I extended my lower control arms by 3/8" to return the wheelbase to stock and re-center the wheel as well as lower the pinion a bit. This helped bring my u-joint angles back in phase, but it's an old driveshaft so can only do so much and those joints are still at about 4 degrees when 3 or less is optimal for long term higher speed road use.

The 45 mph onset of steering shake is definitely suggestive of a lateral tire balance issue. Balance beads and the like cannot influence lateral balance (they address forward roundness variations) and those issues can be difficult to fix as they can require a lot of weight on one side of the rim. If your tire shop is using weights inside the rim only, it is very likely they have not sufficiently addressed lateral balance on a more aggressive tire. If you told them not to put any weights on the outside of the rim, don't say that next time .

Also check your PSI - I would not be running big tires at the PSI often recommended here based on converting from p-metric. That turns your truck into a brick. I run 37" BFG ko2 at 29 PSI on 8.5" rims because at higher pressures the tires will crown and wander and it is so jarring over bumps. I just bought an '04 Sequoia and could not run down some extra shake in the front and I have access to a friend's for comparison to feel the difference.

I've just upgraded shocks and struts, and the truck had a ton of shop maintenance $$$ thrown at it by the PO. Turns out PO had the 265/70/17 Dynapro ATM at 38 PSI. I put them back to 33 (factory is 32 PSI and this is one size bigger) and everything is nice and smooth again.

Bottom line: I think you have a lateral tire balance issue showing up with side to side steering wobble at 45 mph and both driveshafts have alignment issues showing up at consistent higher highway RPM (68 mph).

Both issues are definitely curable. Getting sick of lateral tire balance issues finally is what got me to ditch trxus MT for BFG ko2. That tire is silly civilized for being a 37 and I don't have any balance weights on the outside of the rims for lateral balance issues. Although I did pay an extra $10 per tire to Discount Tire Direct to get the extra tire/rim diagnostics and it's possible that $40 meant they had to find me 4 perfect tires for the rims I bought at the same time. Either way, the result was money.

Words to the wise following this thread: if you are going more than 4" in lift, you can either buy the expensive kit that addresses the extra complications or bleed it out. Not a critique of our OP, just a reality. 80's are very tolerant because you can get a lot caster back by converting the stock driveshaft in its broken back design by shifting to a DC shaft. Usually you just have a DC from the factory and lift reduces caster one for one. Or you have IFS

I would don't a need for using a DC in the rear driveshaft, 10 degrees is not a lot of operating angle for those particular ujoints. Plus if he sets his pinion angle right, it will improve the operating angle of the shaft a little more. The nice thing about single ujoint drive shafts, is they are easy to service on the trail or at camp.

 

[skyline223]

Thank you very much for the continued input. Every bit of advice helps. I wish I could continue experimenting on this issue but the dang truck just blew the throttle body bypass hose so I'll be tearing into that before I can get back to my vibration issue.

In the meantime - I ordered a set of Slee adjustable upper rear control arms to correct the rear pinion angle. After the advice here and further research I have convinced myself that a lift of my height needs those whether it is the source of my issue or not.

In regards to the height of the lift, the front in-particular, how would I go about lowering the front? The truck used to sit very level until the addition of the slee rear bumper, RTT, and storage drawers. Now it is nose high and I wouldn't mind the front coming down 1.5"-2" or so.

Nay - In regards to the lateral tire balance issues, I would love some weights on the outside, but as far as I can tell it may or may not be possible with the Method NV's "simulated beadlock" outer lip. Is there some method that perhaps I'm missing? (no pun intended) See photo of wheel below:

Just another thing throwing out there.. anyone with a recommended "highway driving" pressure on the Mud Terrain KM2s 35x12.5? I'm running them about 45 psi now. I'll be honest I'm not sure what optimal pressure would be for these.

 

[canman]

No expert here, but as @Nay has mentioned the stance does not look right at all. I agree that the rear pinion should not be pointing down which is likely a result of all the additional weight you have added to the rear. Were the rear springs rated for that additional weight which is probably in the 500-600 lb range? I have the 2.5" OME heavies up front with Slee 1" spacers and have never had anything close to a "death wobble", even though I have negative castor with the orig driveshaft. I would start with the stance and either upgrade the rear springs, or reduce the lift on the front if you can live with that. I have 35s with a 2.5" OME lift and had no issues, but added spacers up front to level out the stance.

 

[BlueCruiser84]

Seems like you are not doing the cheap diagnostic stuff. OR I missed it. OR you have done it and didn't tell us. You need to help us help you. It's very difficult to diagnose something like this over the internet.

My last 3 80s have all been lifted and not had any caster/driveline angle correction. They all buzzed/vibrated at various RPMS. Two of them had tire balance issues which completely overshadowed the slight vibrations from the driveshafts. I had an fj40 on unbalanced swampers whose rear pinion was pointed like 10 degrees high or something ridiculous. I could easily distinguish between the unbalanced swampers and the terrible driveshaft vibration.

You need to figure out the source first.

Swap tires. See if anything changes.

AND/OR

Lock the CDL, pull a driveshaft and drive around.

With the adjustable rear arms you can dial the rear in so you know the angles are perfect. However, My current 80 is the same height in the rear as yours with no correction and it runs fine - these things differ vehicle to vehicle, though.

 

[BlueCruiser84]

Lower the front with shorter springs. Or lots of additional weight.

 

[Nay]

Thank you very much for the continued input. Every bit of advice helps. I wish I could continue experimenting on this issue but the dang truck just blew the throttle body bypass hose so I'll be tearing into that before I can get back to my vibration issue.

In the meantime - I ordered a set of Slee adjustable upper rear control arms to correct the rear pinion angle. After the advice here and further research I have convinced myself that a lift of my height needs those whether it is the source of my issue or not.

In regards to the height of the lift, the front in-particular, how would I go about lowering the front? The truck used to sit very level until the addition of the slee rear bumper, RTT, and storage drawers. Now it is nose high and I wouldn't mind the front coming down 1.5"-2" or so.

Nay - In regards to the lateral tire balance issues, I would love some weights on the outside, but as far as I can tell it may or may not be possible with the Method NV's "simulated beadlock" outer lip. Is there some method that perhaps I'm missing? (no pun intended) See photo of wheel below:

Just another thing throwing out there.. anyone with a recommended "highway driving" pressure on the Mud Terrain KM2s 35x12.5? I'm running them about 45 psi now. I'll be honest I'm not sure what optimal pressure would be for these.

IIRC, you have OME Comp springs. Maybe just swap the front for OME J's if the known difference between those springs is 1.5" or so? Or OME heavy? Just a shorter OME spring since that's what you are running, but others can help with that spec more than me because I don't like buying a bunch of OME springs that never really work together .

I want to be careful advising you on tire pressure, so I will only say this again: I run 37x12.5x17 BFG AT ko2 and I run them at 29 PSI, maybe factory 32 PSI if I'm going to be a lot more loaded. 29 PSI is not a recommendation, just a point of reference and contrast. So maybe just try what Mr. T. recommended for your truck, which is on the door sticker and should be 32 PSI, and see if you can feel a difference.

I think I mentioned this before, that I just bought a '04 Sequoia and the front end (IFS) was just shaky over any bumps, but never into a full wobble. Swapped out the struts for some 5100s and still there (better), and this truck had shop maintenance for everything. Turns out the Hankook Dynapros were at 38 PSI. Put them back to 33 (factory spec is 32) and all shaking gone. That's a 32" tire, and you are running 35's at 45 PSI.

You may be right about your rims. But if you have lateral imbalance, which is hardly atypical on a large MT, weights on the inside may have a hard time curing it, and that 45 mph point is exactly where lateral imbalance shows up. Not sure what to say about that one, although at 45 PSI, you have a variable that might be worth...varying...

 

[Nay]

I would don't a need for using a DC in the rear driveshaft, 10 degrees is not a lot of operating angle for those particular ujoints. Plus if he sets his pinion angle right, it will improve the operating angle of the shaft a little more. The nice thing about single ujoint drive shafts, is they are easy to service on the trail or at camp.

No disagreement there. Standard u-joint shafts are preferable, but we have a lot of years and miles, and at some point those things are going to vibe some. My angles are only about 4 degrees and are equal, and it's still growling some from time to time. Between the stupid I have to grease it every other day or it thuds and it getting bitchy with me, I probably come out recommending something new on 20 year old rigs.

But not "needed" - question is what standard u-joint driveshaft do you replace it with if you can't get it happy? Spicer stuff?

 

[Grim Reaper]

another vote for lock the CDL and pull the front shaft see if the problem goes away.

The PO of my truck told me he had a lot of vibration till he put in a DC shaft. It has caster correction and with the lift it was way outside its operating range.

Wheels:

Factory wheels are 16x8 with 0 offset.

What are those wheels?

If you draw a line though the king pin or ball joints ideally that line would intersect the pavement center of the tread.
As the diameter of the tire increases that intersect point moves to the outside edge. The fix is moving the wheel out to keep the geometry close to stock.

 

[Blondie]

Two things. First, pull the front track bar/panhard and inspect the bolt holes. These can ovalize over time making it impossible for the track bar to do its job. Easiest and cheapest step that I don't think has been mentioned yet.

Second, I do not believe those are hubcentric wheels. Pick up some hubcentric centering rings to see if that tales care of it.

 

[9780LC]

^ This and......

Check your steering arms. The holes in the steering arms, the tie rod ends go through on mine ovaled out and created a violent death wobble under braking for me.

 

[n00g7]

A few things jump out here:

Next steps: first you have to ensure alignment on that front shaft. Once done, get an alignment and see what your caster readings are. If low, the front end can wobble including actual death wobble, but that is usually brought on by hitting a bump.

Then you most likely need a DC rear shaft with adjustable upper control arms to set that pinion angle properly (tilting the pinion up until the pinion and u-joint are operating at the same angle, or -1 degree for the pinion to account for torque load that will raise it a bit into line under throttle).

I'm going to go with this for now, esp if he's not feeling it in the steering wheel.

 

[skyline223]

Sorry for the delay - finally have some progress to report.

I spent the morning replacing the throttle body water bypass hose. Yesterday I traveled to Birmingham and picked up a set of stock rollers.

How about this. After installing the stock wheels with 275s, I took it out on the highway and it was smooth as butter. There might have been the ever so slightest low frequency vibration at 75 mph, but overall the difference was night and day with the stock wheel/tire combo. Clearly my BFGs ride like total crap.

I'll still be addressing my pinion angle issues, but it seems that they are about 5% of what is contributing to the rough ride. I've got to figure I have at least one tire that is out of round. Figuring that out for sure, and then determining what to do about it are my next steps.

Grim Reaper - the wheels are Method NV 17x8.4 with 0 offset and 4.75 backspacing.

Blondie - the Method wheel fit very snug around the hubs, but I'll check into those hub centric rings. Those are very interesting.

Looks ridiculous - rides like a Cadillac.

 

[Blondie]

Glad you've got it narrowed down.

 

[Blondie]

Check this:

Slight annoying vibration finally cured!!! Hub centric vs lug centric

 

[skyline223]

Check this:

Slight annoying vibration finally cured!!! Hub centric vs lug centric

So I did some research and turns out that the Method NV hub bore is 108mm and according to info found here on 'mud, the 80's hub is 108mm as well (someone correct me if I am wrong). So if I understand correctly, the hub centering rings would unfortunately not be applicable to my wheels.

I guess my next step is to figure out how to get the balancing beads out of there, and then take it back to have my wheels balanced for the third time.. hope that is the charm.

 

[AussieRedneck]

I've been following this thread. Great information! I have km2's as well. Probably my same problem.

 

[skyline223]

To update-

I took the truck to a competent tire shop to have the wheels balanced for the third time. The first tire balanced out very well, but the second tire showed a major issue immediately. You could tell that it was severely out of round just spinning on the balancer. No amount of weight would improve the lopsidedness of the tire.

The insane thing is, the next two tires exhibited the same issue. Three out of four of the tires on my rig are severely out of round. These tires have approx 1500 miles on them with even tread wear. I contacted Tire Rack about the issue and they agreed to exchange the three defective tires for new replacements.

I received the replacements today and will install tomorrow. Very anxious to see if these tires are better than the previous. Will report back.

 

[skyline223]

RESOLVED!

Diagnosis: 3 Tires out of round

The three new Mud Terrains issued by BF Goodrich have solved my problem. The truck rides like a dream on the highway now that all of my tires are officially "in-round." Now that I have a good set I will say that the KM2's are the best riding mud tire that I have owned, that is, when they are round!

Thank you to all who have helped me narrow down this issue. It is very frustrating to troubleshoot a problem like this but feels great once the root of the problem is found. Time to go enjoy some camping just in time for good weather!

 

[cybrstar]

Okay I'm not going to post a chapter of a book here but....

I've had many fzj' sin the past and all previous had caster plates to compensate for the caster adjustment. All were lifted with 850's in the front on down (roughly 3.5 under). Looking at yours you are clearly over 3.5.

Now for my current ride, I bought it pre lifted already with the maf caster correction roughly 3 inches with the 850's ome Spring. I've driven it on the freeway and I've noticed more of a sway over hilly freeways(not even) going over 70mph which is kinda freaky compared to what I drove in the past. It's okay and bearable, but still scetchy.

Okay for your issue. You have the maf caster drop too. Your over my lift so looking at the maf website they only make brackets up to 4 inches and after that you have to press in bushings to compensate for more lift......

For theory. Dropping the arms down with the bracket does correct caster. BUT think about the stability the strength of the tower and the amount of stress it would take to keep it in place when going at high speeds. I think that the higher the bracket, maybe less stability, and more sway at high speed. I'm no scientist, nor am I a structure engineer.

I think the only way to fix it and go with such a high lift is either brace the sh!t out of it (drop towers) or go with a longer arm or different linkage up front like this...

FJ80 Front Suspension

Just my opinion. End of chapter 500