Violent shakes over 50mph

I had the same problem years ago on my 98SE.

Freeway speed, drive over some uneven section of road and violent shakes, scary, dangerous and embarrassing.
I would describe it as tank slapping, (a motorcycling term for a similar scary thing that happens to riders from time to time)
I changed the suspect steering damper first up, as it was on the way out, but like you, still had the problem, as bad or worse.

After reading the numerous posts here and considering all the different things others have tried, I can only come to one conclusion:

The inherent design of our truck's front end is such that, with a particular combination of wheels, tyres, toe in, shock absorbers, and steering box adjustments, there is a natural resonance , which at a certain critical speed the front end can be set off like a bell ringing. Set off by a disturbance, a bump.
Once it starts, it just self excites and keeps going, until you get away from that critical speed.
You can be fortunate, in that for your car, the critical speed for resonance is so high you never reach it.
Others are not so lucky.
Changing components can change the resonant point so much, that it no longer is an issue, or if the components you change have basically the same characteristics, the problem remains.

As with all resonance circuits, a good damper can kill the vibrations or prevent them from starting up.
Some cars will have the problem worse than others of course, and then even a good damper may not help.
All of the above is just my theory of course!

Did you change the steering damper with a genuine one or an aftermarket one?

Why I ask is because after a lot of checks, similar to what you had done, for some mysterious reason, I decided to pull out the new damper and check it on the bench.
It was an aftermarket one, from the UK, (I am in Australia).

The damping was good and firm in both directions but when I applied small back and forth movements rapidly, there was a small amount of movement possible which was not damped at all. About 10mm to 15mm.

That was enough for me. I bit the bullet and purchased a genuine article, at about twice the price.
That was one of the best decisions I have ever made,.
After installing it, no more violent shakes, ever!

I know that it does not fix the underlying cause, but bear witness to the many who have effectively had to change the whole front end to get a result.

My problem may have been different to yours of course, but, I have done over 100,000k now since fitting the new genuine steering damper, and no more death wobbles, even once.

Good luck and cheers.

Rich,

Good advice as always, your record on this forum speaks for itself.
You are right of course, nothing beats fixing the problem at the source.
The problem is in finding the source.
For some it's clear and obvious.
Others seem not to be able to find it, no matter how much time and money they throw at it, short of replacing everything.

Saying that a good steering damper simply masks the problem though, is not necessarily correct.
It can be a bit like saying that your suspension dampers (shocks) are masking a problem with the wheels bouncing up and down excessively after you hit a bump.
Good shocks cure a bouncy car. Do you then go and fix the underlying problem, ie, the axels being able to move up and down on the springs.

The dampers are an integral part of each dynamic system, not just a masking item.
As I said earlier there may be not much wrong, but the steering system may just be inherently close to a dynamic resonance, and it doesn' take much to tip it over the edge. I still remember the issue vividly. It was not like something was loose, it was a genuine resonance that built up and persisted even when the road was smooth. The steering wheel was moving back and forth so forcibly, I could barely hold it, and I certainly couldn't stop it. I had to slow down as northy did.

By all means replace any faulty or worn componenets, that's a given. But as others here testify, that will not always fix the issue.
I guess I was lucky. I had the problem very severe. Two separate suspension specialists checked out my front end and steering components and could find nothing wrong, out of adjustment, worn, or even suspect, yet the problem persisted.
Now some 5 years down the track everything is still tight, no shakes and all I did was fit a good damper.

So good luck with your issue roversnorthy, it could be anything.
This is a great forum though, is it not?

Cheers all

Quick summary of how I dealt with this problem:

Problem: At highway speeds the car would go into violent shakes, requiring me to reduce speed to get it to stop. VERY scary! Hitting a bump, or imbalance in the tires might set this off at any time, usually over 55MPH.

Step 1: replaced steering damper. Waste of time.
Step 2: checked ball joints, seemed ok. Had shop check them, along with tie rod ends and steering link. All seemed ok.
Step 3: replaced tie rods. No change.
Step 4: purchased full set of blue polybushings and ball joints to basically replace every part in the front end.
Step 5: replaced ball joints. While they were on the car, I could detect no visible play, and neither could the shop. Once off, they were VERY worn (I think top the worst). At the same time I replaced all the front bushings (radius arm to chassis, radius arms to front axle, panhard rod). Test drove and problem was better, but not 100% gone. Still would happen, but I would not have to completely stop once the shaking started, and the shaking was not as bad.
Step 6: purchased used hubs, as the hubs were basically the last thing to replace. Replaced with no difference. At this point I am pretty pissed.
Step 7: After driving the car for about 8 more months like this, I wonder if the polybushings were too soft, even though they were made for the rover. I purchase a pair of used radius arms with rubber bushings still in place.
Step 8: Replace the radius arms, which basically changes the bushings back to stock except for the panhard rod which I left poly. Test drive and problem is basically gone. I purchase 2 new stock panhard rod bushings and replace. Problem is 100% gone.

Lesson learned: The problem was probably close to 100% worn ball joints. The nature of the radius arm/axle setup with non-leaf springs is that there is tremendous stress to keep everything in place. The worn ball joints caused enough of a problem to start the death wobble. When I fixed the ball joint problem, but added the too soft poly bushings into the mix, the axle could still move enough to death wobble. Basically, any serious worn part, or a bunch of slightly worn parts, can cause death wobble. This problem is common in any vehicle with this setup in the front (some Jeeps!).

If I were you I would check things in this order:

1: ball joints
2: tie rods/steering link
3: hub bearings
4: bushings

-Coach