Edit: This thread started as a hunt for the cause of death wobble. It transpired that the steering box needle rollers had collapsed. I'm exploring whether the steering box can be rebuilt with a bush instead of the needle rollers, much like early Range Rover boxes.

OK, so like most other Landy owners at some point, I'm chasing down my Disco's death wobble. Like one of those brain teasers - "the butler and Mr Smith are not the same person... Jane and Robert went on holiday together in 1997... the butler won a shooting competition in 1978", some of the following facts will be critical, some won't be relevant, and the picture probably won't be complete:

- The truck needed a passenger front swivel when I got it about 12 months ago.
- It didn't have a death wobble when I bought it.
- I changed the front swivel in good time before the last MOT 4 months ago.
- The death wobble did not begin immediately after the swivel (seal and bearings) were changed, but it began sometime thereafter and worsened before the MOT
- The MOT tester flagged Panhard rod bushes, which I've now replaced with polybushes. Briefly thereafter, the truck rode like it was on rails, but then the wobble came back. It also flagged passenger front wheel bearing play, which I've tried to fix...
- There is some play in the passenger front wheel, but this doesn't seem to go away when I re-tighten the bearings (putting some decent torque on them, then backing off 1/8 turn and locking with a new lockwasher, then tightening the second nut as hard as it will go and locking it in turn)
- I removed two shims from the passenger swivel this evening but the wobble persisted
- Driving above about 45mph on a back road is not much fun - go over a bump or two and the wobble will begin. Backing off the power and waiting for the speed to bleed off makes it go away. On a flat, smooth road, there's no wobble - it needs a bump or series of bumps to set it off.
- Applying the brakes doesn't reduce the wobble; in fact, quite the opposite - it becomes more noticeable and (I think) persists to a lower speed. I'm better allowing the speed to reduce on its own.
- I don't think the vibration frequency is speed dependent but am not 100% sure
- The track rod ends don't show obvious play, nor does the drag link, and the steering box doesn't let me rattle it when I grab the drag link and jerk it around.
- Worn-out steering damper has been replaced to improve driveability; I realise this doesn't fix the fault. No obvious improvement.

Later additions based on questions asked in subsequent posts (thanks all)
- Tyre pressures are all at 30psi

I'm quite confused. If I hadn't already reset the wheel bearings, I'd say they were the culprit... but I've done them more than once and still no joy. It's possible that my technique is adrift, but this isn't the first Disco I've worked on and it hasn't caught me out yet. Also, applying the brakes doesn't reduce the wobble - if it's just the wheel bearings, shouldn't the brakes reduce play, not worsen the situation? Does this behaviour indicate that the problem is at the back of the vehicle, and the weight shift under braking is leaving whatever is free, freer?

So... once again I'm here asking questions rather than actually contributing to the forum. I hope that's OK...

check all your suspension bushes, i had the same thing after changing panhard rod bushes and discovered my radius arms bushes were so shot the arms had 5mm of play each way in them... it eventually destroyed the tie bar on the steering box and suddenly wobble was at 20mph and not 40mph...
Also check wheel balancing and pressures.

The wobble is the result of play/vibrations in the suspension hitting resonance (1st mode natural frequency) which doubles the amplitude of the vibrations... hence sudden "oh shiii..."

Tyre pressures shouldn't take much checking and would explain the slow onset. I'll check the radius arms too - they're uprated but look fairly rusty so might have been on there a while. It's behaving like a classic underdamped system; I hadn't considered that it might have happened because I stiffened the system (Panhard rod) and moved the first mode up to where it could be excited. Food for thought - thankyou.

Edit... Tyre pressures are all bang-on 30psi. How do you go about checking the radius arms?

Pre load on the swivel hub when you changed it?

They are big heavy wheels and once the wobble starts it will find the weak points until you notice.
Start with simple things like tyre pressures and balance then get into the bushes which are almost always a good bet for wear.
Little confused on your wheel bearing comment, they are not difficult to set, if your not happy change them, simple job to do and something you must have faith in.

thetim said:

Edit... Tyre pressures are all bang-on 30psi. How do you go about checking the radius arms?

Click to expand...

It probably won't help much, but your tyre pressures are a bit wrong for a Disco.
They should be closer to 30 psi in the front and 38 psi in the rears for unloaded running. Increase the rears up to 45 psi when towing.
If in doubt, check out the "tyre pressure chalk test" on the forum.

Thankyou all for the pointers. The swivel preload was right when I set it; I did wonder whether the bearings had subsequently seated themselves a little better and opened up play, but yesterday I removed two shims from the swivel and went for a drive - no improvement. Reverted it quickly lest the increased preload kill the bearings (thereby giving me yet another source of wobble and confusion).
I agree - never struggled to set the wheel bearings before and don't know why this one should be any different. It seems if I leave any free play in the bearings (i.e. I don't wind them up monster tight and leave them, which obviously isn't going to work) then the wheel wobbles. I'm split between "I'm being incompetent" and "something else is going on".
I'll boost the rear tyre pressures too - as you say, might not help but should at least be right.

Death wobble is no fun!
Wheel bearings are unlikely as a cause. As already suggested look at swivel pre-load. Panhard rod and radius arm bushes would be next on my list followed by the steering damper - you did "prime" the steering damper when you fitted it didn't you?
It would also be worth checking the drop arm is not loose and that the steering shaft UJ's are not worn. The only other thing I can think of is freeplay in the steering box so maybe tighten it up a bit and reduce the backlash, also check that all the steering box mounting bolts are tight. HTH

I agree you should reset the swivel preload properly in accordance with the manual, before you look elsewhere. I think it can settle, and the correct preload is important it seems. Just taking shims out without checking is not accurate enough.

Couple of pretty easy checks first, especially if you're sure the swivels are good, and all the bushes and wheel bearings tight, with no apparent problems.

I'd first start by removing the wheels/tyres and swapping fronts to rear and seeing if it makes a difference with no other changes. I'd also check the springs are seated correctly, the dampers mounted correctly with good bushes, indeed drop the dampers and check they work properly over their full travel .. pull them fully out and push in fully, there should be no freeplay, stiction or sounds of bubbling, do it a few times!

Then I'd check the track rod ends on both the draglink and steering trackrod, that they're sound, working and tight. They should rotate smoothly without being 'easy' to move when done up, but without being massively stiff or jerky. If necessary take each rod off and move the end by hand so you can tell properly if it's rotating fully or just moving a little and then jamming. I'd check the radius arm bushes at the chassis end, undo the big bolt, see if they expand out or are solid. Awkward but not too hard to swap out.

Then I'd take a wheel and hub off and check where the outer races sit and where the inner races sit on both the hub and the stub axle and make sure there's a proper fit between them. If a ball race can rotate in the hub or on the stub then you effectively don't have a wheel bearing! Then do the same the other side.

I'd also check tracking for too much toe out, toe in will (should) make it more stable, but too much makes it reluctant to turn. I've found 1 degree toe out to be ideal.

For a start fit proper bushes to the Panhard rod NOT poly bushes.

Ah, that's interesting, Paul - the the track rod feels smooth, but I can rotate it (as a unit, not unscrew / tighten it) by hand with no real resistance. It's not sloppy and will stay in the orientation I leave it, but it's certainly not stiff. Should it be tighter than this?

Yes, there should be some resistance. Try holding it and jerking it, try to feel if it knocks at all. It may be that one end is U/S and the other good. If you remove it, it should be easier to feel a 'bad' end. Hard to explain in words ... should need pressure to move smoothly, without being too easy .... Same for draglink, easier to check off, I think.

Undo the track rod nut, but leave on the threads, then use two hammers, one on the holder where the taper is, and hit the other side of the holder ..... DON'T hit the trackrod itself, you'll damage threads. The nut is left on so when it drops out it won't fall through completely .. In the pic (NOT a Landy) Hold a hammer against where the yellow arrow points to, and hit where the red arrow points to .. easy as. Or use a puller ..

Hit it directly on the end with the pip on it.

thetim said:

.... How do you go about checking the radius arms?

Click to expand...

Grab hold of the bottom of the bend in the radius arm, where it goes under the axle, and try to give it a wobble and try to move it side to side. Like any other bush it should be stiff and not move easily (at least not by hand anyway)

As earlier swap wheels front to back and test.
Then dig in for bushes an sing ore wamers as polys do worl, least they do on a rrrc for many many miles

As a starting point I've acquired another wheel bearing kit - may as well rule out bearing wear and get a good look at the stub axle while I'm at it. Radius arm bushes seem OK (no major movement) but I've changed them in the past, usually involving setting the old bushes on fire and waving it around like a caveman (the waving doesn't help but it feels good)...
It'll take me a little time to get opportunity to do the rest (bathroom is currently unserviceable) but I'll definitely be having the track rods etc off for a closer look in due course. Thankyou all for the generous advice - I'll report back if I manage to cure it.

Does the vehicle have standard suspension height? A radius arm suspension action lifted/sagged can effect front axle swivel castor angle and make it prone to the wobbles.This is the reason "cranked" arms are used on radical suspension lifts, just athought.

Resurrection of my old thread - I hate it when the OP asks a question and never comes back with the answer. I tightened the steering box up tonight via the adjusting mechanism - a 6mm allen key on top of the box, locked by a 19mm nut. Slacken the locknut while holding the allen key bolt in place, then turn the allen key clockwise and tighten the locknut again and check steering play. Apparently you should do this gradually, about 1/8 turn at a time. I've tightened mine a fair bit; the steering feel hasn't obviously changed, so I don't think I've overdone it, but (so far) I think the wobble is gone. I'll post back if I'm mistaken.

thetim said:

Resurrection of my old thread - I hate it when the OP asks a question and never comes back with the answer. I tightened the steering box up tonight via the adjusting mechanism - a 6mm allen key on top of the box, locked by a 19mm nut. Slacken the locknut while holding the allen key bolt in place, then turn the allen key clockwise and tighten the locknut again and check steering play. Apparently you should do this gradually, about 1/8 turn at a time. I've tightened mine a fair bit; the steering feel hasn't obviously changed, so I don't think I've overdone it, but (so far) I think the wobble is gone. I'll post back if I'm mistaken.

Click to expand...

you must do that adjusting when box is in central position, and adjust till theres no freeplay in input shaft

Ah, pants. The wobble has gradually returned. Something is deteriorating, evidently. A garage had a look over it and couldn't find anything obvious, but didn't check the steering box itself, which was what led me to adjust the box and get some temporary respite from the wobble. I'm now wondering if the steering box is dying and allowing misalignment of the worm and sector. Doesn't appear to be leaking, at least.