Hey there Fellas,

Saw this forum, and thought this was a good place to find some help. Just bought a 1994 Ford F-150 XLT Short Bed, manual. The truck is in great shape. The engine is clean and sounds great and the interior is as well. The issue is with these violent shakes the truck has been doing.

The Problem: After driving the truck around for about 20 minutes, and then accelerating/driving over 60mph for the entire truck will violently shake/buck, and will not cease until you come to a complete stop. One of my mechanic buddies researched it and thought it was a stabilizer shock and put a new one on; however, the problem has still not gone away.

I did some research, and apparently this is a common problem, but I do not see to many people who have found a fix for it. Also, we recently installed a new pitman arm, and the truck still needs an alignment after we put on the new stabilizer shock. Is this the mythical "Ford Death Wobble" I am experiencing? If so, why does this happen, and how do you get rid of it?

- Thanks.

 

Maybe I'm way off the mark, but I once had a '76 F150 and severe shakes would occur whenever I shifted. The problem, according to several mechanics I spoke with, was common. Oddly, no one seemed to have a clear solution.
After replacing the clutch and having the flywheel ground down, the worst of the shimmying went away, but after a little while it would return!

Of course, your problem doesn't seem to be related, but I had tried different fixes, such as pitman arm replacement, new shocks, etc.

By the way, have you looked closely at the transmission and engine mounts?

 

Thanks for the response "MildlyInsane." I just wanted to post up here some more research I found on the Death Wobble that was validated by an older guy I know who knows more about cars/trucks than anyone I have ever met. The post came from another site, and it is long. I pasted it below, please share with friends who have suffered from this problem...

"Here's an engineering description of DW. I get tired of seeing people guessing at what's causing their DW, so here goes. Hope it helps someone.

First, you've got to realize that the front suspensions on our vehicles were marginally stable, at best, from the factory. DW is a fundamental dynamic response mode of the entire front end...as a system. Lift and larger tires change (increase) the 'gain' associated with what becomes (or even starts out as) a marginally stable dynamic system. The damping factor (lambda) is also affected by larger tires...it decreases as a function of sidewall height/thickness ratio. Hysteresis in any control path (loose tie rod, steering box, track bar bushing) reduces the ultimate stability margin further. The fundamental frequency of DW is determined by the superposition principle where all springs involved are resolved (frame, tire resilience, hub bending, bushing deflection, etc, etc.) into one global spring constant, and all damping factors associated with friction, elastic elements, viscous damping (steering damper and shocks) are resolved into one damping factor. The natural frequency, damped natural frequency, and damping coefficient are then known. Now, if the system is overdamped and the gain is low...no problems...no oscillation. Increase the gain without increasing the damping and you go toward the critically damped, and beyond, specturm of responses. Critically damped means that DW would only 'hint' at being there, but would die out on its own without going totally unstable. This is also known as a decaying response.

Once the system goes beyond critically damped, any excitation, be it an unbalanced tire, a bent wheel, bumps in the road, etc. can set it off and the response will not decay...it will grow in amplitude, quite quickly in some cases, and may be limited only be physical non-linearities like hard stops...or breakage. That's classic Death Wobble.

A truck suspension is designed to stay in the overdamped to critically damped range. That is generally why a truck rides "rough". A Cadillac, on the other hand, is designed to stay in the undersprung range. It just "floats" down the road. Any change in the basic design parameters that affect the gain (e.g., lift, tire size, wheel backspacing, etc.), damping (tire size, steering damper, steering box condition), and hysteresis (any wear point that creates any slop) can push it over the edge and create DW. ANY ONE OR TWO of the factors discussed can do that...which is why everybody then thinks that whatever problem THEY found and fixed is the cause of all DW; it is not. It is plain and simply a marginally stable system in its original form that is easily made unstable by any of the myriad causes discussed already.

If your front end is loose (bushings, bearings, etc.) then you have a situation where your stiffness is removed and any jarring sensation (potholes, unbalanced tires, misaligned wheels, etc.) will cause the suspension to go crazy. It is no longer functioning where it is designed. On the other hand, your suspension could be very tight but an imbalanced tire would be spinning at just the right speed to throw the suspension into a unstable situation.

So unfortunately there isn't only one root cause to the problem of DW. The underlying problem is instability in the front suspension, the root causes can be a multitude of things ranging from bad/loose bushings, to loose bearings, to caster angles, to imbalanced tires, etc.

OKAY, HERE'S THE REALLY USEFUL INFO:

A steering damper only hides (maybe) the effect; it does nothing to fix the root cause.

There are two types of DW. The first typically is speed related. Whenever you reach a certain speed, bam, you get DW, no matter what. This is a vibration/oscillation issue. Look into tire balance, alignment, steering joints, missing bushings (totally shot), loose steering box (either loose bolts or worn internals), etc.

The second is an impact initiated DW. For example, hitting a pothole above a certain speed will start DW. This is more likely a bushings, loosening mounts, flexing components, etc. issue. Basically, something is tight enough that in general straight driving, it is ok, but give it an impact force, whatever is getting loose starts sliding, rebounds and starts going nuts.

Here is how you can tell if the issue is steering related or trackbar related. You are gonna need some ***** for this, but stick with me. Once you have played around with the DW awhile you find you can control it a bit by feathering the brakes. So go find a straight, deserted, bumpy road. Get the truck up to speed and get the DW going. You had it happen a few times, you have already been frantically avoiding potholes, so now go find one, quit whining. At this point, the truck is somewhat violently shaking, and you can keep enough control using the brakes to keep it on the road. Roll down the window and stick your head out and look at the front tire. What is it doing?

1. The front of the tire and the back of the tire are moving approximately the same amount side to side. In this case, the axle is stationary, and the wheel is pivoting on the ball joint during the oscillation. Therefore the problem is likely in the steering. Something in the steering has enough give to allow the movement.

2. The back of the tire is moving MORE than the front of the tire in the side-to-side movement. In this case, the knuckle is pivoting on the steering links, and allowing the axle to move back and forth under the vehicle. The problem here is most likely in the trackbar system.

This doesn't really answer a question about what's causing YOUR DW, but it should give you something to think about in your search for the root cause(s). I'd check the trac bar bushings, make sure your wheel bearings are in spec, make sure your tires are balanced, make sure your alignment is in spec - especially caster, make sure your ball joints & TREs are tight, see if you have play in your steering box, etc."


I thought this was great, and also explains why you keep hearing different solutions from people who have this problem. In follow up, I had new and better sized tires put on my truck and when they we're about to do it they noticed that the "I Beam" was not connected properly after the lift job was done and there was an inch of give either in the passenger side tire. I think this, along with an alignment and balancing will fix the issue.

Will update the post with the final solution...

 

Thanks, Wolfpack Ford,

That's some seriously informative writing! I'll have to read more from that guy.
This information would have been a big help to myself and others more than a few times. I'll have to study some of the concepts I don't totally grasp yet...
So much of what I do understand makes so much sense, I just nod my head and smile. Thanks for sharing it with me. My friend's Chevy Suburban has a serious case of the DW. The laws of physics don't seem to play favorites with brand names.

 

Nice post, Wolfpack.

 

Replace the center pivot bushings. Noone ever does this and the factory rubber is only good fer about 40,xxx. Just my experience from driving all generations of twin I-beam trucks. Rich