Running out of ideas - death wobble at <30mph

[Eightpot]

Have you tried getting it up on axle  stands front & back and running it to see if you can see anything obvious as the wheels/props are turning?  

[Dave W]

I've experienced this kind of death wobble many times on mine, normally indicates that one of the TRE's has some play in it. Once it starts the only way to stop it is to come to a standstill, very scary sometimes. It seems you've checked the normal stuff though.

However, I did have the same issue many years ago on a Range Rover Classic with road tyres on and it took about 6 months to diagnose. Everything was tried, damper changed, everything adjusted/tightened, checked etc... Turned out to be the tyres, changing front to back made no difference but borrowed a mates wheels and tyres and no sign of the problem. New tyres fitted to the original wheels and the problem went away. There was nothing visibly wrong with the tyres and the only conclusion was that the tyres were distorting and took a while to return to normal again. We figured out it always happened after a bump in the road, even the tiniest pothole would set it off, even running over a cats eye.

If I were you I'd borrow a set of wheels/tyres and see - if nothing else it rules the wheels/tyres in/out as the cause of the problem.

[miketomcat]

I've got bfg 255/85x16 km2's on the 110, so we'll try them at the weekend. Don't worry I will take photos.....it's going to look sooooo silly. 

Mike

[muddy]

Id start by swapping wheels and tyres completely. 

 

If you get it up on axle stands and drive it you can get an idea if the wobble is from rotational mass (wheel still swaps sides quicker than a French traitor) or from loaded components like the swivels (no swappy swappy)

[SteveG]

I had this once with HD track rod, I’d obviously smacked it hard, but the HD tube lived up to it’s name and it stripped the threads on the TRE inside the tube and as soon as it was under lateral load driving it would move, but if you checked it when it was standing there it wouldn’t feel like there was much play in it.

[FridgeFreezer]

Well Mr Tomcat is coming over tomorrow to complete a thorough investigation of the kettle & biscuits... and maybe help me get to the bottom of this if there's time after that

The suggestion of putting it up on axle stands & running it is a good one if my garage floor didn't slope back toward the door a tad so will have to move it all outside to try that, otherwise the failure mode is quite a big mess one way or another!

[Wytze]

It's in my head ..  would like to know/find out what the problem is😁  Not close enough to come over and help

[simonr]

My bet......Steering Damper

Most other things (other than play in TRE's etc) seem to manifest at 50mph+  Steering Damper seems to at around 30.

That's my experience anyway!  The bushes on mine were fine but the damper itself had almost no resistance in the middle of it's stroke, where it spends most of it's life.

[FridgeFreezer]

@simonr - good guess, except there is no steering damper and never has been...

[Bowie69]

That was the reason prop was suspect, very low speed.

[deep]

19 minutes ago, FridgeFreezer said:

@simonr - good guess, except there is no steering damper and never has been...

I understand not wanting a steering damper.  They damp self-centring and make the steering annoying.  However, on a setup that will amplify ANY lateral problem (I mean, what is there to control sideways movement other than a small number of long, spindly leaf springs and tiny rubber/plastic bushes?), I would have been dead scared not to run one.  I've seen how even fitting bigger tyres on larger offset wheels can make a standard and well maintained Land Rover suddenly terrifying.   Fitting one now might mask the problem but won't fix it, of course.  In the future, it might save you when something goes a little bit out.  Even picking up a stone on a large tyre could trigger a wobble if your speed amplifies a resonant effect.

Your original post didn't make it clear that you had successfully run this setup (well, not to me but I had just had surgery and that seems to affect eyesight...).  That would have helped diagnosis.  If it worked fine before and doesn't now, something has clearly broken, unless you changed something.  A stripped thread, a delaminated bush, something jammed inside a swivel etc..  Surely you will find that by systematically going through everything.  Getting the wheels off the ground to check seems like an excellent plan.  Maybe with rear propshaft removed?

There's a lot of interest in this post, as lots of us stand to learn something from it.  I look forward to seeing what transpires to be the issue.  My money would be on something causing your castor to change (twisted spring?) due to the shopping trolley behaviour you describe.

[Wytze]

Did  you make anti wrap bars on both axles, Fridge? 

[miketomcat]

First order will to poke, prod and look at (whilst drinking tea ). Then we'll move on to letting fridge drive down the road whilst I'm safely outside.  probably move on to some hanging out of window/door. by this point it'll be cold, wet and dark. 

Mike

[Wytze]

1 minute ago, miketomcat said:

First order will to poke, prod and look at (whilst drinking tea ). Then we'll move on to letting fridge drive down the road whilst I'm safely outside.  probably move on to some hanging out of window/door. by this point it'll be cold, wet and dark. 

Mike

Bring a flashlight😁

[daveturnbull]

I can picture it already... Passenger floor removed, with Mike upside down in the seat, head through the floor, having a good nose at what's going on underneath, cruising round baisingstoke.

"Well, officer, er, you see, we were..." 

[Anderzander]

I more imagined, with the ridiculous ground clearance, the car up on axle stands the size of pylons and you both sat under it with a table and chairs, drinking tea and looking for wibbily bits.

[Bowie69]

Clearly need to remove the tyres to do that

[Eightpot]

Yeah you'll need some big ass stands with portals, and it does feel mildy scary when the wheels are spinning off the ground, though just ticking over at idle will probably show up the problem, found similar probs this way in the past. Some kind of dead mans switch might be sensible  - string tied to the diesel solenoid wire 😬

[Wytze]

3 minutes ago, Eightpot said:

 - string tied to the diesel solenoid wire 😬

It's a petrol V8😋

[De Ranged]

Sounds like you've covered all the obvious ones, normally I find death wobble is due to not enough caster, bigger the wheel sidewall the more caster you need... (on a soft sidewall tire), In your case your axle was designed to run a HD truck sidewall so going to a 4wd tyre should mean you want a couple of degrees more  

Now since yours has run alright caster is most likely not the issue, but it doesn't rule it out, you can bandaid close to bad caster with tight balljoints, steering, track rod etc.... I've had to deal with a few 4wd's that have been on the road or in the bush for yrs without issue and this was the cause 

You state the track rod bj are flogged given the leverage from the portals that would be my first thing to look at now you've done king pins, if your track rod is able, try pulling more caster into the front axle try it you might find it improves the tracking 

One other couple of things that could be adding to the slop allowing this are loose wheel bearings and worn leaf spring bushes, but if you caster isn't enough it could be a combination of serveral of those allready mentioned and possibly these two 

I'd discount the Drive Shaft UJ's, normally they are a droning noise that turns into a teeth rattling vibration.... I've never had one feedback into the steering like death wobble 

For those that don't understand caster and why I'm putting this forward 
First you need to understand why your wheels return to center (straight ahead), this is because it is the low point, when you turn your wheels you wheel tilts down slightly lifting the front of the vehicle the biggest cause of this is King Pin Inclination angle (This is the angle off vertical that kingpins tip in) unfortunatly as builders and modifiers we can't change this on a solid axle it is fixed by the manufacturer. The next one that effects the return to center is caster, (the tilt back along the length of the vehicle from vertical) what this does is applies more lift from the inside (if cornering) steering wheel and we can adjust this.... my go to is generally 2-3 degrees more caster than factory

Now to explain my comment about softer sidewalls and why we need to compensate with more caster.... due to the king pin inclination as you turn you are tilting your tyre slightly similar to adding camber so you load up the inside sidewall this sidewall gives you the lift that causes the self centering.... with our bigger tyres and softer sidewalls the lift just gets soaked up  

[Eightpot]

13 minutes ago, Wytze said:

It's a petrol V8😋

Oh arr - well the job just got bigger, we need to fit a nice diesel first 😄

As de ranged says there may be something to the castor angle business, doesn't take much to knock a shopping trolley off kilter though I don't understand the dynamics myself. I think if you can run it with the wheels off the floor you can separate dynamic balancey issues from gyroscopicy ones. 

Edited November 26, 2021 by Eightpot

[FridgeFreezer]

All good thoughts chaps - just wanted to make sure my responses were being taken as "adding information" rather than "dismissing suggestions"... as I'm definitely still stumped and will try anything... fingers crossed Mike and I can execute some daring heroics tomorrow and maybe make some progress, possibly even learn something

 

@deep - no steering damper on the Volvo or on the Series (although it was an option), I've never needed one (it's always ben very well behaved even at motorway speeds, towing, etc.) so I prefer not to add anything like that if I don't need it.

@Wytze - yes, anti-wrap both ends although I've never liked the front setup as I think the geometry is all wrong, the bar is too short but that's what there was space for at the time;

It's on my to-do list to re-engineer it

 

@Anderzander and @Eightpot - yes I do have a set of HGV-sized axle stands I picked up from Sodbury a few years back for this very reason the height makes working under it much easier but also brings a few challenges...

 

@De Ranged - The Volvo trucks the axles come from run very similar tyres/sizes (9.00 x 16 is factory fit) and are similar weight rating, the 4x4 being 3.5t gvw, and the axles are mounted to leafs almost identical to the setup on my truck. I've just checked the Volvo manual for the spec;

• Caster 3 deg
• Camber 1 deg
• Kingpin inclination 8 deg
• Toe in 0-3mm
• Wheel inclination 31-32 deg

I'm not sure if I said the track rod BJ's are flogged - they're 3/4" heims from EMF Rod Ends which are rebuildable and adjustable and have been adjusted up for zero play (and fairly tight in fact), they make LR and Volvo TRE's look very small and are ultimately living a pretty easy life -  they take no more steering load than a LR running the same size tyres (which are only 37x1250, so only about an inch bigger than Volvo stock), and there's lots of folks running around in Defenders heavier than mine with the same size tyres and stock TRE's.

 

Anyway, the quest continues, I'll update tomorrow!

[Wytze]

Is the kettle on yet? 😁

[miketomcat]

58 minutes ago, Wytze said:

Is the kettle on yet? 😁

I hope so I'm leaving shortly........

Mike

[Wytze]

Will be good to know what the cause will be.