Hi guys,

So I have noticed this since I bought the car, but haven't thought too much of it (and have been spending time 'debugging' the symptoms, so to speak).

In a nutshell, when I am at speed (typically over 90 or 100 km/h (over 55 mph)) I notice a sort of low-pitched harmonic vibration (which I can both hear and feel). I can't really localize where I feel it - I can feel it through my seat (though it's not a strong vibration) and through the armrest. Not through the gearshift at all. The vibration is not constant - it's more of a vibration that gets weak, and then strong over the course of about a second or a little longer.

If I shift into N while driving, and take my foot of the go pedal, the vibration is totally unchanged. I imagine that if I were really interested, I could shift into N, take my foot off and then even go so far as to turn off the motor and it would still be the same vibration.

If I let off the gas (while still in D, at speed) the vibration becomes a little stronger (but only slightly).

Turning the wheel has no effect.

I'm a bit stumped. Maybe I just need an alignment? The car doesn't pull perceptibly to either side. Tread wear is even so far as I can tell across all tires. Maybe I have a wheel that's out of balance? All my other tires are correct pressure.

My passenger-side rear tire is low on pressure (by about 6lbs) so I wonder if it could be this. I'll be repressurizing it tomorrow and we'll see if that makes any difference.

Any other ideas I should be exploring?

Crawl under and have a look see at the center bearing, try to rotate it. Sounds like maybe it could be on it's way out. Bearings usually give you some warning. Sound and/or vibration.
Otherwise, you may have a rear wheel bearing issue, harder to localize.
Mentioning "seat of the pants" usually refers to something in the rear of the car. Check trailing arm bushings also.
Good luck, and keep us posted.

__________________
83 SD

84 CD

You will find it at the front end of the rear driveshaft.

I just replaced my center bearing assembly last week. I had no idea how SHOT it was!
Had symptoms just as you describe.
Nice and smooth now. Less than 30$ in parts, about 1Hr worth of your time.

__________________
"Any sufficiently advanced technology is indistinguishable from magic"
-Arthur C. Clarke

"I won't be wronged. I won't be insulted. I won't be laid a hand on. I don't do these things to other people. I require the same from them."
--John Wayne.

OBK member#16
77 300D
75 300D (rusty parts car)
73 220D (Dad's)
98 Jeep Grand Cherokee
82 Kawasaki M1

You did say less than thirty cents right? That seems to be the recurring theme I keep hearing here. However, here in Canada (or at least Metro Van) I've been looking at the local junkyards, and no-one even has mercs! The only pick-n-pull with mercs is run by a guy who obviously hasn't heard the mantra that Merc parts are cheap. He wanted $100 for a gauge cluster housing I won't even dare ask him how much the emblem and badge costs

Anyway, for the totally uninitiated (moi) could you please tell me what parts are required for replacing the centre bearing assembly thanks!

__________________
1987 300TD
1984 300D
755,000 KM and going strong
BC Canada

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=28D0KHXF229B0NRNCK&year=1984&make=MB&model=300-DT-001&category=K&part=Driveshaft+Support
http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=28D0KHXF229B0NRNCK&year=1984&make=MB&model=300-DT-001&category=K&part=Driveshaft+Support+Brg.
http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=28D0KHXF229B0NRNCK&year=1984&make=MB&model=300-DT-001&category=K&part=Drvsft.+Support+Boot

And, two of these, if you want to do a complete job:

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=28D0KHXF229B0NRNCK&year=1984&make=MB&model=300-DT-001&category=K&part=Drive+Shaft+Flex+Joint

I must admit, since buying the car I have not had the wheels balanced - and now, I certainly will have it done. It can't hurt, after all, and might be a cheap (and simple) solution that doesn't require me to get greasy!

I think I want to replace my center bearing just on general principle now though - looking at the service records, I am quite certain I have the original bearing, so it may not be looking too hot these days.

__________________
1984 300D Turbo, 326000 Km, Thistle Green Metallic

Tire balance?

__________________
1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

hmm! I hadn't considered the centre bearing. How big is it? I am sure it will be easy to spot. Let's say it is going bad... how difficult should it be for me to replace?

Its about 4' across and takes a few horrs to replace. Check out and replace, if needed, your flex disks whole you are working on the driveshaft.

__________________
1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Only if you have a heavy duty driveshaft!!!

Imagine how heavy that'd be...

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

4' sounds about right, becuase by "1984 300D" I really actually meant "my 1984 crude oil tanker" hehehe

Great! Reading some other threads here, it looks like replacement basically consists of pulling apart the driveshaft at the spline, and marking it to reassemble the right way. With it apart, I can pull out the replace the bearing?

Time to check out my FSM...

Hey xdjio, let me know when you're doing this. Maybe I could swing by to help out (and learn a bit too). Even better, if we could get Bens Lover around too, if he's available...cos then we'd have someone who really knows his way around the stuff .

__________________
1987 300TD
1984 300D
755,000 KM and going strong
BC Canada