||08-09-2013 02:09 AM
While I'm sorry to hear about these troubles, I'm relieved that I'm not the only one who's had weird vibration problems. My '07 CRD has had an intermittent high-frequency vibration for years now, and I have never figured it out.
It began to occur about four years ago when I got a small, portable motorcycle trailer...one of those that can be disassembled and tossed into the back of the truck. It's called "Trailer-In-A-Bag" in fact. Basically, it's a crucifix made of 2" square tube with the wheels mounted directly onto the ends of the short arms...tube flex is the suspension system. I hooked it all up with my bike on it (about 800 lbs total) and took it for a test run around my area (Milwaukee, WI). I found that on certain stretches of road and at certain speeds (45-55 mph) that the whole rig would very gradually begin to vibrate, starting as almost nothing and gradually, slowly increasing in amplitude until the whole setup (Jeep and trailer) was vibrating like a huge tuning fork...in character, the vibration feels just like driving over the the most aggressive continuous chatter strips you could possibly imagine. Looking out the back window at the trailer, the tires/axles were actually blurred, they were vibrating so badly. At lower or higher speeds there was no problem. I tried all different combinations of tire pressures, etc. to no avail. Of course, I assumed that the trailer was at fault so I contacted the manufacturer and he bent over backwards trying to solve the problem...swapping parts, providing different tires, etc. Nothing worked in the end. Then I decided to take a trip out to the west end of South Dakota with it. I went fast/slow for quite a while and eventually noticed that, once I crossed the state line from Wisconsin into Minnesota, the problem disappeared! It was fine for the rest of the trip until crossing back into Wisconsin on the way home, when it started again. Somehow, the smoothness/flatness or whatever of the roads in my state just happens to excite the condition, whatever it is, that starts a cascade, or feedback event culminating in a vibration so bad that the whole truck feels like it is about to explode. Naturally, I quit using the trailer, and everything was fine...for a while.
Not long after that came time for a new set of tires, and since the OEM Goodyears had served so well, I went to them for the new set as well. The new tires were slightly less off-road oriented...I forget the model, but they run quieter. A while later, about a year and a half ago, I was driving along one day (no trailer) and the vibration started again, the same way, gradually building to an outrageous level...only now it no longer disappears when I slow down. It continues until I stop completely, and often resumes when I start again...unless I reverse briefly after stopping and then start forward again. Then it usually disappears. I agree with those here who say that the frequency of the vibration happens at drive shaft frequency, not tire frequency. And, I have to say that varying tire pressures, tire rotation, and even the new different type of tires, have had zero effect one way or the other.
Last week when I was replacing my exploded serpentine belt, I spent a little time just laying under the truck and looking at things. I'd never really noticed the whacky rear drive shaft before...it looks like the back half is made of aluminum and the front half is made of some kind of composite or plastic, etc. Then, there's some kind of odd-ball flywheel thingy at the front end of it...and that "flywheel" is the single most rusty part on the entire truck, by far. We're talking you touch it and big chips and flakes of rust fall off of it. I've never seen its like before. I started wondering if maybe it's one of those dual-mass deals that might be there to quell vibration because of the diesel or something like that. If it is a dual-mass device, I wonder if it has somehow developed some excess slop under certain loads that might let it get out of alignment a bit and cause the vibration. Or, what if the rust has caused enough of the parent metal to shed from it that it's now been thrown out of balance...though that would cause vibration every time it turns, which doesn't seem to be the case. What about a bad transfer case mount? You can see that I've been running around in circles with this for quite a while now. Sorry to drone on about it...I was just hoping my story, along with the others, might cause a light bulb to click on with somebody who could explain this, or at least start us looking in the right direction. This thing really has me stumped... :brickwall