I’ve been reading the vibration threads purely from a professional interest. My F150 has no vibration problem (SCAB, 5.4 liter, 3.72 L/S, Tow Package, etc.). I’m a physicist by training with practical experience as an engineer and 30 years of wrenching as a driveway mechanic. I’m a newbie and this is my first post, be gentle.

There are several issues that come to mind on the nature of the vibrations described, but first we need to come to a common definition of terms.

First… everything that rotates vibrates; drive shafts, tires, rims, ring gears, engines, etc.

Then, there is resonance. This is what is being experienced.

Every rigid system has a characteristic or natural frequency. In other words, if you were to suspend your truck from a rope and smack it with a giant hammer it would ring like a bell.

Every system can be forced to vibrate. For example, if you had a big rock in your tire you would feel a bump, bump, bump that increased with speed. The same is true if your crank was out of round. This is forced vibration.

Resonance is when the forced vibration is the same as the natural frequency. When resonance occurs large amplitude vibrations result, (Note: the forced vibrations that cause resonance can be very, very tiny. Too small to notice. )

Imagine a kid on a playground swing. If you push her in random shoves she just vibrates about the equilibrium (bottom) position. If you push her at just the right time or frequency, you get large amplitude vibrations. This is resonance.

The fact that your trucks vibrates at specific speeds if proof of resonance. If it where forced vibration you would feel it at all speeds.

There are at least two scenarios.
1. A single system is vibrating and at certain speeds, resonates. This might be the case say of a tire. It vibrates at all speeds, too small to be noticed, but at 56 mph (whatever) it vibrates at its natural frequency and you get large amplitude vibrations that you feel. This could be true of any rotating component; driveshaft, ring gear, transmission, engine, etc.
2. A single system is vibrating and causes a second to resonate. Say the driveshaft vibrates (they all do to a certain extent) and at 60 mph its vibration rate is the natural frequency of the frame, the frame is driven into resonance.

My gut feeling here is the frame is the resonating object. When I drive my truck over a bump I feel the frame ring. There are two ways to eliminate the problem.

1. Replace or modify the component that drives the frame into resonance and hope it doesn’t have the same vibration characteristics.

2. Change the natural frequency of the frame. The natural frequency of on object is determined by its mass (weight) and how that mass is distributed (its shape). Ford’s vibration dampener is their attempt to change the frames natural frequency. It’s hard to tell how successful its been from the limited data in this forum.

Option 1 requires a cooperative service department. Lets face it, there are lots of rotating components and finding the right one to replace for your particular vehicle is hit or miss. It’s very expensive and time consuming to do a trial and error replacement of every rotating component until you find the culprit. And you may never find it. The culprit vibrates, but it is still within manufacturing specifications. In other words your differential vibrates and drives the frame into resonance. It’s replaced with a unit that is within spec, but also vibrates, and drives the frame into resonance.

The obvious culprit here is the driveshaft. It’s the first thing Ford replaces. If it were me I’d get two stainless steel hose clamps big enough to go around the shaft. I’d tighten them with the heads 180 degrees apart. Mark the positions, crayon, chalk, etc. Then I’d rotate them towards each other. I don’t know how many degrees, 10, 20 then drive the truck. There are three things that can happen: nothing, things can get worse, things can get better. Them move them another 20 degrees. Mess with it. Rotate them in the other direction. I don’t know about the long-term effects on the needle bearings in the u-joints. But at least in the short term it may identify or eliminate the drive shaft as the problem. Maybe this is a totally stupid thing to do, I’m on shaky ground here. I know there are mechanics with way more drive shaft experience than myself. If you’re out there, speak up.


I think the key is option 2. Small changes in the frame’s shape or mass can have dramatic effects on it natural frequency.

Changing the shape is the best solution, but the hardest to do. The shape can be changed by drilling a hole, cutting a slot, adding a cross member, taking one out, welding a plate (changing the thickness), etc. But what to do, and where? This is where Ford engineers earn their salaries.

Changing the mass isn’t easy either. But for lack of anything better to do I’d put a couple hundred pounds of sandbags in the bed (the bed is bolted to the frame and thus can be considered part of the frame system, the cab and engine are isolated from the frame, somewhat, by rubber mounts). Try various positions, over the left wheel, over the right, by the cab, etc.

Another thought. As boxy trucks move through the air they make whirlwinds. It’s why the leaves/debris in your bed collect near the cab. You see the whirlwinds come off big trucks as dust devils on the shoulder. This process is called vortex shedding. If the vortices shed at the right frequency they could drive the frame into resonance. Try dropping the tailgate.

Hope this helps.

 

I dont know whats worse me reading that post at 1am or you typing it at 1am. In either case thats a lot of info, and althought im no expert in those areas I do understand all of what you said...However, I think the major concern here is that if the average guy like myself buys a 35-40 thousand $ truck, they dont want it to vibrate, shake,rattle, whatever, and the last thing they want to do (nor should they have to) is put hose clamps on their drive shaft and rotate them around to get the proper balance needed to rid them of their vibration, nor should they have to put sand bags in their bed, or drive with the tailgate open. Like you said, to figure out the problem is why the ford engineers make the big bucks. I think THEY need to get under the truck and tighten some hose clamps, lug 50lb bags of sand around the bed and figure out the problem,create a solution and fess up and fix all the trucks affected by this vibration.

I personally dont have the vibration 12,000 miles and going strong, no problems at all. I think there should be a list compiled of everyone with the vibration, check the bill of materials on those trucks and find the common thread. At least it would be a place to start and not just pi$$ in the wind and throw parts at a truck and hope the problem or the customer goes away. I feel for those who have the problem, and hope Ford comes up with a fix for it soon.

A word of advice..ifyou have a small chip in your windshield and its a nice hot day out and all the windows are rolled up, dont spray cold water on the windshield...unless you want to see what looked like a snake slithering from the top to the bottom of my windshield. Needless to say the glass man will be coming to my house next week with my new windshield

If Ford ever gets the vibration issue fixed I wonder if they could invent rock repelant for our windshields!!!

OH..1hfmv2, welcome!

 

That was an amazing first post.

I'll be coming to you with any problem I need explained to me.

 

I must give thanks to be one of the lucky one's to have got a smooth running truck thus far.... Almost a year old October 03 just about 5000 miles.... have had my PCM updated with a download from Ford... for the temp guage but thats all so for....GG

 

Good first post. It makes a lot of sense, but as someone said. if you thought of these things then a couple dozen or so Ford engineers should have as well....and yet, still no fix. They've had to know about it for several months if not more now. I bet they know and instead of changing the frame manufacturing process (read: $$$) they are trying to throw cheaper fixes at it.

I'm curious if the 2005 model production will have a production (material) change. That would be the obvious time to make some changes due to re-tooling.

 

I can answer that as I know he typed it well before 1am (as I read a pre-copy before publication).

So, I guess what I'm saying is that it was worse that you read it. HA!

Seriously though, that's an excellent piece of information and we're really glad to have you aboard 1hfmv2!

RP

 

Excellent tech info! I never thought of pushing a kid on a swing as having anything to do with resonant vibration. Cool analogy.

 

GEE thanks RP, your making me feel great.LOL,

Hey what else would you rather do at 1am when you cant sleep...

And your right, it is a great post with some great info

 

1hfm...one simple question.

Assuming that the drivetrain vibe is a driveshaft or rear axle issue as one of the TSBs implies (I'm referring to the vibe that occurs at 50-65 mph and GOES AWAY WHEN THE TRANNY IS PUT IN NEUTRAL), what does the tranny engagement have to do with eliminating the vibe SINCE THE MOTION/ROTATION OF THE DRIVETRAIN (i.e. everything aft of the tranny) REMAINS THE SAME as long as forward motion/speed of the vehicle is not altered.

The only change is the absence of torque application to the drivetrain via the tranny.

 

Welcome to the forum 1hfmv2

No amount of information will be able to explain why most trucks don’t have vibrations that rise to the level of annoyance. My truck is smooth at any speed towing or not. Of course I have the normal vibration you get from driving on imperfect roads, but some of these vibration complaints, if true, are way out there, especially the bed shake, which I also don’t have.

 

Thanks 1hfmv2

Great post!

 

LOL! Just poking at ya Brew! HA! Seriously though, there have been many times that I've been on f150online.com at 1am. ... more times than I care to disclose in fact...

RP

 

 

Here's some food for thought:

I bought a 2000 Suburban (1st year of a remodel) and had a horrible rumbling/resonance when going over rougher roads. I found out that other people were also complaining about it so I too complained. Eventually, a TSB came out where they replaced the rubber bushings between the frame and the body. Evidently, the original ones were too hard and did not absorb the vibrations from the road. After they replaced them it rode very nice until I totaled it (I now have a 2002 Suburban).

 

The overwhelming majority of 2004 F150’s are vibration free.

They’re all built from the same parts, what could possible make such a big difference from one truck to another?