350SD driveshaft vibration
 

When I accelerate anywhere under 40 mph, I can feel a vibration channel through the driveshaft. It starts from the front, then works it's way back. If you put your hand around the center bump in front of the middle of the backseat of the 350, you can feel the vibration. However, at 50 mph the car is smooth. Have talked to many owners and they have never run into this before. :(

Perhaps you guys can help me.

bad vibrations:
 

Possible problems.
Flex Disk
Center Support & Bearing
Universal
Drive Shaft out of balance
Good luck.
Charlie

Thanks. I'll try to cover all the bases this week.

A bad flex disk will also cause a thump on downshifts, and a bad center bearing rubber mount will act almost like a bad tranny mount (which you should also check) -- vibration, almost hammering, under acceleration only.

I'd bet your engine mounts are shot too -- take a look at the driver's side (since it's easier to see) -- if you cannot clearly see the tapered portion at the bottom, or the lip of the rubber part at the bottom of the hemispherical metal portion is actually sitting on the frame, or you can see evidence of oily leakage, they are shot. The passenger's side will be worse, but you cannot see it, it's under the turbo.

My guess would be bad engine mounts definitely, and probably a bad flex disk too.

Peter

Behavior
 

The way this thing acts, though, depends on operating conditions. For instance, if it is wet outside, upon acceleration the driveshaft will not rumble as roughly.

In the cold and damp, the vibration almost disappears completely altogether.

* The driveshaft is three-piece, and it has traction control (ASD).

The car has 244K miles. It has had this vibration for the past 20K miles, and it has not gotten any better, or worse.

My S-350 also has just developed a vibration. I installed new tires and went to the dealer to have them balanced and an alignment. I also had the engine mounts changed out. The tech called me and said that there was a vibration at around 60 mph. He said after balancing the tires he re-balanced them again to make sure it was not the tires. He said that the driveshaft, where it goes into the transmission was slightly worn and recomended replacing the transmission mount to bring the driveshaft back up a little. (The engine mounts raised the engine about 1-1.5"). This healped a little but the vibration is still there. His next recomendation is to change out the driveshaft (very expensive). My question is -- would new flex disk help the situation any? I am also going to put a post in the tech help section to see if anyone else has had this problem on a 140 series.

Sounds very much like the rubber mount for the center drive shaft bearing is old and hard, or shrunk. If you can move the driveshaft inside the rubber by pulling on it more than a very slight amount, replace the mount. Bearing can be bad too, but it usually hisses or growls rather than vibrating.

What happens is that under high torque, the driveshaft can go slightly off center if the rubber allows too much movement, and so it orbits rather than spins. When you release the torque, it spins straight again.

Peter

Bad news is that psfred is most likely correct about the center bearing or the flex disk. Good news is that once the car is in the air it will be very easy to check by wiggling and shaking.

Given your description of 40MPH or below, I expect it to be driveshaft related.

Good luck,

Do what Peter said first, because it's the most like cause. But don't forget about the U-joint. I went through this on a 300E and it turned out there was a detent worn in the U-joint. IF that's the case, the tech might tell you that the whole driveshaft has to be replaced and even show you how the U-joint is straked in there so that it can't be replaced. That's what happend to me and the used driveshaft he put in was barely better than the original. However, there are companies out there that can replace the U-joint with a brand new greasable one. Spendy, but not as much as a new shaft.

If it is the driveshaft remove it and send it to Driveline Services of Atlanta. (404) 361-0475. Costs will runn around $250 for a rebuild and balance. Well worth it.

Figured it out
 

The MB mechanic who worked on this car before claimed that he had replaced the center mount and bearing in the driveshaft. Turns out, he only replaced the bearing.

Thanks for the help,