Trying to diagnose a shimmy

[nelstomlinson]

The '89 f350 has started shimmying - rough road will start the front end shuddering and shaking, and the only way to make it stop is to hit the brakes and stop the truck. Of course, all our roads are rough, and icy.

The front axle is the dana 60 with king pins, and I'm not familiar with those. How can I tell if the king pins need to be replaced? I tried jacking up the front and levering up under the tire with a shovel, but I couldn't see any vertical slop like I'd expect to see with ball joints. I tried rocking the tires around a horizontal axis (grabbed top and bottom and shook), and there was maybe a little give on the passenger side, definitely a little squeak on the drivers side.

The tierods are tight. I don't know the truck's history.

How do I determine whether it's bearings, king pins, or something else entirely?

 

[Micah Lay]

Get a friend to get in the truck and turn the wheel with the truck off. Most loose steering parts won't be apparent until the leverage of the box is used to attempt to move the linkage without power. Also check the track bar and bushings. If the track bar is damaged or the bushings are shot it can cause a shimmy in the front, more commonly referred to as the "death wobble"

 

[Rusgo]

My death wobble in the same axle was causes by kingpins. Everything in the steering is way easier to verify and replace though. Definitely the place to start.

There is alot of weight hanging on the kingpins with the vehicle off the ground. Can take alot of force and leverage to see any play there.


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[nelstomlinson]

Bushings! I should have thought of that. Russgo, I was denting the tire and slightly compressing the spring with that shovel. I had 100+ pounds on that shovel handle, and loads of leverage.

Thanks, both. I'll check steering and bushings tonight, after work. We're in the middle of a chinook, so it's wet instead of cold. Ick!

 

[DaveBen]

I have had death wobble in four Ford trucks and Jeeps. King pins were the cause in 3 outa 4 death wobbles.

 

[nelstomlinson]

I was reading the manual last night about king pins. They look like a much bigger pain than ball joints. Just in case, I have a Snap On IMA283 coming from ebay. I'm really hoping that it's something small, because I'm way behind on projects and no time to catch up.

I bought a bunch of projects over the last several years, and I'm driving them. I haven't had time to fully go through anything, so nothing is 100%. Things keep coming up, and the urgent keeps getting in the way of the important. In five years or so I'll be sitting pretty, with lots of old but reliable equipment. Getting there is going to be painful.

Fixing this is urgent, but it's going to be hard because I have a loader in the shop that will take some time to finish and get out of the way. I'll probably have to do this outside in the cold, rather than wait however long it takes to get the loader out of the shop. By the time the parts get here, it's probably going to be cold and miserable. At -20F, you spend five minutes to get a couple of bolts started, then you spend 10 minutes to get the feeling back in your fingers.

 

[nelstomlinson]

I don't know if I found the problem, but I found a problem. The oil streaming from the engine rotted the bushings on the track bar. I have changed the bushings and I'll test drive tomorrow.

 

[nelstomlinson]

Looks like I got lucky. The new bushings in the track bar seem to have solved it. I drove down the stretch of road that reliably triggered the shimmy, and it's gone.

When I reinstalled the track bar, I stuck the upper end in a plastic bag. Maybe that will shield the bushing there from the leaking oil for a while.