Hey folks! 1994 F150, 5.0L, 2WD, 255K miles, 8' bed, second owner (bought it in 2001). I'm having a problem where the front wheels will sometimes start to shake at moderate to high speeds. Sometimes they shake really bad (higher speeds) and when I apply the brakes, it seems worse until they quit shaking. My first thought was a loose caliper or axle stud. I inspected the lug nuts, calipers, brake pads, rotors, axle studs, coil springs, shocks, and the control arms and everything is tight and in good physical condition. I do not see any 'scars' where something has wobbled (like a loose nut or bolt). With the truck on jack stands, I can grab one of the rotors and wiggle it. When it wiggles, the controls arms and the other rotor also wiggle and I can see the pitman arm and the shaft in the steering gear box also wiggling. The pitman arm itself is not loose. I'm wondering if the steering box has some slop in it and could be causing this. I tried loosening the nut on the adjustment screw but it and the screw are turning together (probably dirt). I went ahead and loosened it a few turns (CCW) but it did not have any affect on how much things wiggled. I don't mind replacing it but I don't want to just throw parts it. Any help is greatly appreciated.

 

1) Shaking “wheels” at higher speeds.

When was the the last time and mileage you had the tires balanced? Do you rotate your tires every 6K miles?

2) Shaking really bad when you apply the brakes

Sounds like too much runout in the rotors ie the rotors are warped.

3). Im not sure what an “axle stud” is. Are you taking about the upper and lower ball joints?

Loosening the preload adjustment would only make the issue worse. That adjustment in very small increments will take a bit of the free play out when the steering is centered. Tighten it too much and you can damage the steering gear.

 

First I'd like to pick a nit here, maybe to help clear things up (or maybe muddy them!). And it's not you, it's just I can be a nit-picker sometimes.
A wiggle/shimmy/wobble/death-wobble is helped along and even encouraged by loose or worn components, but it's actually "caused" by the tires. In my opinion, tires every time. Does not sound as if you have a full blown case of the "Death Wobbles" yet, but it actually does sound like it's trying to get there.
Also not saying you can't fix it by replacing something like the steering box or so, just wanting to point directly to the culprit. The tires start the dynamic motion, the rest of the stuff just stops it in it's tracks, or helps it along to getting worse.

With that in mind, and if it seems everything is tight (more on that in a minute) I would rotate the tires front to back. If you want you can have them re-balanced, but I usually recommend that as next in line, because rotating is free if you do it yourself in your own driveway. Balancing takes a bit of justification if the tires are older and maybe near the end of their useful life.
Speaking of which... How old and tired are they? And are they road-only tires, or have they seen some off-road or farm/ranch use in their day? This can make a difference. Even a single "curbing" going into the drive-through can damage a tire enough internally to cause this symptom to start. Been there, seen that many times.

Regarding the testing, now that you've one it the traditional way with the tires off the ground, try another test with them fully on the ground and the full weight of the truck on them. That's where you have a helper rack the steering wheel back and forth (approx. 1/2 turn in each direction) continually back and forth while you watch all the steering, brake and suspension components. Pitting the torque of the steering system against the weight of the vehicle is a sure fire way to see something that's working itself loose, but was still tight enough to resist hand movement.
You can see really small increments of movement with this test method.
If you do it with the engine on though, it helps your nerves to have a helper you trust a lot!

Back to the steering box, as was said that's not really a wear adjustment screw. It's the initial backlash setting method, and should only be changed by a slight amount. Since you went looser, you're not likely to have harmed anything, but I would try to get it back to it's proper location to make sure you have the best steering your box is capable of. You might have to read up on it though, or watch some YouTube videos where the people sound like they actually know what they're talking about. If they don't specify why, when and how the adjustment should be made, move on to the next video maybe.

Anyway, good luck with tracking it down. Maybe it's something simple and cheap (is it ever?) but it's simple and cheap to check the tires. If the action changes at all when you rotate the tires, even if it doesn't go away fully, you're on to something.

Paul

 

My4Fordtrucks and 1TonBasecamp, thank you both so much for all the information. You both pointed at the tires possibly being the problem, whether an internal problem or needing to be rotated and re-balanced. The tires are over a year old and haven't been rotated or balanced in a long time. I generally drive a few miles a week but sometimes I need to get on the freeway and this is where the issue will pop-up, especially if drive over some obstruction such as a pot hole. The tires are Goodyear Wrangler 235-75 R15's and haven't been off-road. Since the front-end is already off the ground, I'm going to go ahead and rotate them front to back to see if that makes any change to the issue.

The rotors and brake pads were replaces a few months ago so I don't think the rotors are warped but it's not impossible. If all else fails, I'll have them checked out.

I had a lot of front end parts replaced around the time I had the rotors and pads replaced. There is one component that still needs to be replaced but I cannot recall which one it is. The part and labor was going to be $850 and I had to put it off because I ran out of money. The service manager said the truck is going to drift to the right a little (and it does) until that part is replaced. Other than the drifting, the truck has driven fine. I had to take it back to the shop for something to be adjusted (don't recall what) and the problem started at that time. I took it back to shop some time later and the mechanic, the service manager and I all went over the truck together and could not find anything loose. I don't recall if we tried shaking the tires.

I like the idea of "Pitting the torque of the steering system against the weight of the vehicle" and will try that after I rotate the tires.

Thanks again for all the information, I greatly appreciate it.

 

Great. Keep us updated on what you find. Always interested in what causes each case of wobbles.
A true Death Wobble (I don't know if I was the first to use the term, but I've been using it since the early eighties at least) will shake the wheel out of your hand and cannot be "driven through" as some wobbles can. It will only go away once you reach a certain low threshold speed where it finally goes away.
But it is a very repeatable problem as well and can be re-introduced by hitting a certain bump in the road at a certain speed. In the old days it always seemed to be around 28-35mph or so, but in recent years especially with the Jeeps it seems to happen more often at higher speeds of 55-65mph instead. Maybe it's a difference it tire design, or suspension design, or perhaps common steering geometry. And while it does seem to happen on solid front axle vehicles more, it's not exclusive to that. My first experience with it was in 1970 on a '67 Buick Wildcat with about 50k or 60k miles on the original tires. Second time was on my '71 Bronco in about '78 or '79 or thereabouts.

As mentioned, yours does not sound like a case of the dreaded DW's yet. But it's got some of the symptoms, which made me think of tires.
The getting worse with the brakes applied is consistent with tires too I feel. With a warped rotor you will start to feel it initially as a pulsing pedal when braking, usually well before you see it crop up in other symptoms. If your truck normally stops perfectly smooth with no pedal pulsing, likely your rotors are still ok, but perhaps the wheel bearings are showing some signs of age. Speaking of which, how long since they've been re-packed and re-adjusted? I'm assuming that in '94 the 2wd trucks still used standard tapered roller bearings and not a unit-bearing setup like most modern vehicles have now? I don't actually know, but it's my "assumption" that the bearings are still of the old adjustable type.
But they would normally have checked that as well at the shop, as part of their testing procedure. So presumably (there's that assuming again!) they did not find anything.

Sorry for rambling on so much just to keep the conversation going, but it's fun to talk about all the possibilities when something just starts to make itself known with our old trucks!

Good luck.

Paul