W124 Highway vibration while accelerating
 

My 89 300TE recently started to hum/vibrate around 45 mph while accelerating or going up hills. It seems to get worse as speed/throttle increases and it happens in any gear. There is no/low vibration while coasting. The vibration has been slowly getting worse over the last few months. I occasionally use it to tow a utility trailer (approx 2000lbs) and it was particularly noticeable when taking the trailer to the dump today - haven't towed anything in about 12 months.

The car has about 230k miles on it, and I've put about 90k of them on it. I have never replaced the flex disks.

I read LarryBible's thread about doing some research before throwing parts at driveline vibration problems, also the part about altering the seat of the U-Joint looks like a good thing to try before dropping the exhaust and throwing flex disks and a center support bearing at it. But Duke mentioned that the flex disk should be replaced at 60k or else bad things happen so I'm wondering if I should just replace them regardless. While I'm in there should I replace the center support bearing? The car had an oil leak at the headgasket (which was repaired about a year ago) but this resulted in the undercarriage getting persistently coated in oil. Can that ruin a flex disk?

About the tires - they're about 12 months old and the MB dealer performed the last wheel alignment. Does this type of vibration seem like a tire problem? Should I rotate the wheels or swap them with my other 300E?

Thanks!

bump:)

Do you have any shift related clunking down there? Best get under and give them a good looking over as 90k is a lot on flex disks. Once you get them changed youll hear/feel any other vibrations that remain. (If you do them... consider the lower shift bushing and tranny mount at the same time)

Thanks for the reply. Is the lower shift bushing the nylon bushing that connects the shifter to the tranny?

I think this is the one:
http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1JV0QMRTI1QU1B4K0K&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1989&product=J4070-44817&application=000046642
...and I believe there is also a clip.
I had my front flex disk just short of come apart on me, in mid February in mid week, in a nice snowy cold spell. So I gave the job to my indie. (Ahh the power of a lift and a warm garage in the winter) He replaced both flex disks, the tranny mount, and the lower shift bushing with the parts I bought from Phill just as the old ones started to crumble, for $150.00 labor. I can't tell you how much better it feels. Smooth non-clunking firm power. ;)
I can feel a little hiccup back in the differential now so I suppose those mounts are next on the agenda. Wish I had done the job myself so I could give you pointers, but alas, I can only testify as to the results.

How fast is the vibration? The driveshaft rotates at something like 3x the tire rpm, so if it's a medium speed "brrrrrr" it is probably more wheel related. If it is a high speed thrumming, it is probably the driveshaft. My driveshaft support bushing problem made a "thrumm... thrumm.. thrumm.." vibration, and it would also appear while accelerating through certain rpm ranges.

It's more of a thrumming - thanks for tip. I'll checkout the center support bearing. Is that the sort of thing that's easiest to replace along with flex joints?

Without having done the job (sent it to the dealer), I will venture that the answer is yes. At a minimum you have to shove the driveshaft back, don't remember if it needs to come out.