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Running out of ideas - death wobble at <30mph


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Well this has turned into quite a saga and as you may guess I've been having one of those days in the workshop - except it's spanned multiple weekends now :angry::(

I've tried to do some methodical stuff and get to the bottom of it but am now fairly stumped - there's a few straws left to grasp at but I'd like to see what folks here make of it.

For those not familiar with my 109 the setup is;

Series 3 109, good (TIC) parabolic springs, Bilstein shocks, and Volvo portal axles.

The problem which has developed is that at any sort of speed from much above walking pace I can get full on death wobble - not unbalanced tyres, but actual full-on "front axle trying to escape sideways" death wobble. Power or coasting makes no real difference, and it happens basically immediately within ~200yds of setting off, so at least it's easy to reproduce the fault I guess :rolleyes:

So I've been over everything I can think of / all the usual suspects to no great improvement;

  • Bushes are all fine, no play in them
  • Mountings / bolts are all fine & tight
  • Steering linkages (column & shaft) are all pretty much new.
  • Steering rod ends are all tight (they're adjustable and rebuildable so I have actually tweaked them right up).
  • Kingpins have no play in them and are shimmed to spec
  • Tracking started as major toe-out (not entirely sure why), adjusted it to toe in (Volvo spec), re-adjusted it to some toe-out (Defender spec) which made a little difference at the speed of onset but not much.

Now the whole toe-in / toe-out thing is a tad confusing as Volvo & Series spec 0-3mm toe-in and Defender specs similar toe-out, and of course the internet provides ample evidence that both are the only correct one :lol: although I've run following Volvo's spec up till now with no issues. I'm not sure if it's more affected by the truck being leaf sprung or by being permanent 4WD. Also I don't know how it got so far "out", only thing I can think is some off-road abuse last time it was out playing

The only thing I am not 100% sure of is the kingpins - Volvo use ball-and-cup bushings top & bottom (think Series / early Defender Railko) which obviously give some resistance / friction, I have converted to use taper roller bearings as the Volvo parts wear quickly and cost an eye-watering amount... however the conversion was done long ago and I've done a lot of miles on them since then with no issues. The bottom ones have been rebuilt (water/mud had gotten in) and shimmed to tighter than Volvo spec - the top ones don't have any adjustment (tension is set by the bottom ones) and are a right barsteward to dismantle, but there's no detectable slack or play.

 

I've been faffing with this for what seems like ages, to the point where I'm now pretty sure I'm missing the obvious, so posting here to find out what I've missed or if anyone's got any good tips? :unsure:

 

The Volvo swivel/kingpin setup in case anyone's interested - upper kingpin is 16 & 17, lower kingpin is 27 & 28, both are now using Defender swivel bearings:

volvo_kingpins.jpg.b8f217c94015c5ac82e8bcf2175a36ff.jpg

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Something like this can be so frustrating, particularly so given the huge amount of time and money you must have put in to get here.  Yet, as I read the description of your setup, I was thinking it would have been amazing if it had just worked without problems.  The parabolics don't have the torsional resistance of standard springs and the portals put the axis around which the power/brakes apply torque some distance from standard as well.  It feels like a setup that would amplify any destabilising influence.  I have had severe death wobble in an early Range Rover and a Series 3, both bog standard other than wheel offset and tyre size but also both tamed with a decent steering damper.

In an attempt to be helpful, I can only suggest the obvious (but sometimes someone you've never met who states the obvious can trigger some helpful thinking!).  Is your rim offset quite big or are your rims tucked in nice and tight, like on a standard Land Rover?  The more offset, the worse the wobble.  Are your wheels properly balance and tyres properly round and identically sized, without any deformities or slight bulges?  Are you using a steering damper and, if so, is it worn or quite stiff?

If everything is as it should be, my guess would be just too much offset weight for the parabolics to handle.  The best solution, which I think benefits all leaf sprung Land Rovers used in battle (due to the way the springs are hung), is to fabricate an anti-torque link between axle and chassis, which stops the axle applying torsion to the springs.  As long as the link is around the same length as the rear shackle to mid axle dimension and it is offset enough from the plane of the springs, it will stop the shimmy which destabilises everything and causes axle hop.  I appreciate that your movement is more lateral than rotational but I think the more stable base will make all the difference.  I also appreciate that I could be completely wrong (I'm still under the influence of an anaesthetic, having had surgery two days ago, eek) but I hope my thoughts stimulate some lateral thinking which could help?

Oh yes, permanent four wheel drive requires a tiny bit of toe out, part time four wheel drive requires a little toe in.  It's just the direction load/drag is put on the tyre as you drive.

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Forgive me if covering ground already trod....

 

Swapped tyres front to back?

Antiwrap setup still on front?

Steering box bolts tight? P38? Spline wear/nut loose?

Loose axle saddle/u bolts?

Broken leaf? 

 

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Have you got Mrs Fridge to watch or film from the outside? Throwing a gopro underneath somewhere might reveal something too.

As Bowie says, have you still got the anti-wrap bar on there? If yes/no have you tried the opposite? 

Have you tried setting the toe to straight ahead? 

Have you got a damper fitted? Thinking if you have it might be worth trying it off or put back on to help work out what is/isn't setting off the wobble.

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Is the wobble in time with the wheels ?

On my ex job, we had a Sprinter van that had a luton box on it, and the rear overhang was such that the rear wheels were just about halfway along the box, which of course put a lot of the payload behind the rear wheels.

Upshot of this was that the tyres would deform. The wobble would be quite violent at some speeds. Couldnt really see much with the tyres fitted either, but you could see the deformation inside when they were removed. New tyres always cured it, but only for a while, I guess because of the vehicle format.

Can you swap a set of wheels or borrow some maybe ? Possibly worth a try.

 

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Definitely toe out for driven wheels as it allows for take up giving you parallel in use.

Check your castor angle has whatever caused the tracking issue rotated the axle, weak spring, anti wrap or moved on the spring seats.

UJ/ prop worth a look as stated.

Have you had this problem since changing your wheels to banded wolf's? They are considerably heavier than modulars and are they/the tyres actually still round. Are the wheel nuts tight?

I could pop up if a fresh pair of eyes help.

Mike

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8 hours ago, smallfry said:

Is the wobble in time with the wheels ?

On my ex job, we had a Sprinter van that had a luton box on it, and the rear overhang was such that the rear wheels were just about halfway along the box, which of course put a lot of the payload behind the rear wheels.

Upshot of this was that the tyres would deform. The wobble would be quite violent at some speeds. Couldnt really see much with the tyres fitted either, but you could see the deformation inside when they were removed. New tyres always cured it, but only for a while, I guess because of the vehicle format.

Can you swap a set of wheels or borrow some maybe ? Possibly worth a try.

 

That sounds like overloading to me? It's surprising how little you can put in the back of a luton.

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2 minutes ago, Diff said:

If sat with low tyre pressure in one place, some tyres will stay out of shape until warm or pressure is increased. This can cause massive wobble with big tyres and may magnify another issue.

Busted CV joint? Not very likely. 

Diff. 

Good shout.... @FridgeFreezerare you still running Creepy Crawlers? They're not radials are they? So deformation whilst sat might be the issue here.

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How is your caster?  If it's near zero or even minus, you will get that shopping trolly thing going.    my front axle is set on 3° .  and i have 0.5° toe in.  All wheel drive aswell..   After playing around you might have changed caster by bending the leaf springs slightly? 

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Almost certain your king pin bearings. No slack or play does not mean a lot; you need to check how much resistance there is. If volvo has a spec, try to achieve it, otherwise use land rover specs or similar. A steering damper can help but it is merely masking the problem. All the other things- toe out, caster, big wheels, permanent four wheel drive all have an influence, but it just comes back to sort the basic problem out, I reckon, which is kingpin pre load.

Daan

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I'll try to respond in order...

@deep

The setup has been working perfectly since ~2007, despite a few minor changes.

Rim offset is pretty standard, I've switched from 8x16 modulars to banded Wolfs but it worked fine with those before this problem arrived.

As others have said, a steering damper doesn't fix wobble, only masks it, so I'm reluctant to resort to one.

Also my steering bars are ~38mm solid steel so they introduce a degree of damping by mass alone :lol:

It's fairly certainly not axle wrap, and I do have an anti-wrap setup fitted, it's definitely side-to-side (violently so).

The toe-out / toe-in thing is interesting and confirms what LR say for coilers Vs leafers, I may re-try toe-out now I've shimmed the kingpins.

@Bowie69

Swapped tyres front to back - Not tried that

Anti-wrap - yes it's still on although the heim joint is shagged it's never made a difference before

Loose U-Bolts - pretty sure they're tight, all been checked and torqued.

Broken leaf - not that I can see

UJ's and props all good, pinion bearing is fine, I really can't imagine a prop or UJ being bad enough to send the axle sideways like it's doing.

@landroversforever

Haven't had a spectator yet but it's on the to-do list

Anti-wrap is fitted, I can try un-fitting it

I've heard that zero toe leads to more issues as it can switch behaviour from slightly-out to slightly-in... also I don't have super-fine adjustment in my track rods.

No steering damper fitted, never needed one.

@smallfry

The wheels do go square with being parked up but this is definitely not the same experience, this is way more severe and is moving the whole front axle / steering side-to-side very violently.

@miketomcat

I'll switch back to toe-out and see what it feels like, previous test may well have been before I rebuilt the kingpins (although there was no play they were likely not shimmed to spec)

Castor is set by the axle sitting on the spring leaf and that's not changed

UJ/Prop see responses to Bowie, I really can't believe it can cause this level of violence.

Although this problem has appeared since fitting the wolfs, it didn't start when they were fitted - also it's at such low speed that balance/weight shouldn't be affecting it

@elbekko

I've checked all the springs, mounts, and bushes but jacking the chassis and giving a wobble could be worth a shot

@Diff

Pretty sure it's not wheel wobble - it happens at very low speed, I've had the tyres go square before after storage and it's a hundred times worse than that.

@daveturnbull & @Nonimouse

I'll see if I can try a different set of wheels/tyres but this is way beyond even very bad wheel wobble.

@Wytze

Caster is set by the axles/springs which I'm fairly certain have not changed in the last ~15years of driving with no problems.

@Daan

Kingpins have been rebuilt with new bearings and shimmed 1st to Volvo's spec (zero play minus 0.3mm shim), and then a bit tighter than that (minus another 0.3mm shim).

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That is my thought , a tyre has given up integrity in favour of self expression :)

A set of known round tyres as Mike suggested would rule out deformation of a tyre . 

Ross' comment on sticking a go pro somewhere to view the action might help to highlight something .

You were running Petlas in the earlier days I think which are crossply ? With no issues iirc ?

How good is the steering box ? Another potential source. 

Steve

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Yes it was still fine with the Wolfs.

Steering box is very good, no leaks, no play.

Steve - I've no idea what the Petlas were but these tyres have been on it a while and don't have any obvious issues, and as I've said numerous times in this thread the shaking is many many times worse than an unbalanced/loose/bad tyre or rim, I've driven with all of those and it's not even on the same page, this death wobble can happen at 10-20mph and yanks the front wheels left & right as hard as hitting a solid rock or stump, except it happens twice per second in opposite directions.

Don't have a GoPro unfortunately but it looks like I'm borrowing a Mike over the weekend to see if the two of us together adds up to a whole brain :lol:

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45 minutes ago, steve b said:

John - it really sounds like a buckled wheel which I can't give a logical reason for .Daft question but are the wheel nuts tight ? 

For it to start at such a low speed something must be fundamentally wrong .

Steve  

Steve,

Wheel nuts are all torqued to Wolf spec, wheels are pretty much new and straight, it's not done anything that would damage one since they went on - a parade lap of Thruxton is about the most excitement it's seen ^_^

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