Noticeable hum at road speeds - PeachParts Mercedes-Benz Forum

spark3542 · #1 08-25-2007, 05:18 PM

I took a 1700 mile trip in my 83 300SD without incident, but the next day after I returned, I had a noticeable hum that I didn't have before.

I can't figure out whether it's coming from the front or rear.

From past experiences on other vehicles, it sounds to me like a bad wheel bearing.

The pitch of the hum increases with vehicle speed. It doesn't change at all with transmission gear, no difference whether on the throttle or off, it doesn't change with braking or steering, it doesn't change with Ebrake applied. I rotated the tires, with no change to the hum.

I pulled the front hubs and repacked the bearings...no change.

I see nothing in my manuals about R&Ring rear hubs.

I inspected the flex discs, but haven't changed them yet.

Point me in the right direction...should I be looking at flex discs, or dry Ujoint in the center section, or axle shafts (the boots look good), or rear wheel bearings, or something else I haven't thought of?

Thanks

toomany MBZ · #2 08-25-2007, 06:33 PM

May be the center drive shaft bearing.

nhdoc · #3 08-25-2007, 07:12 PM

Quote:

Originally Posted by toomany MBZ

May be the center drive shaft bearing.

I'd second this, especially if you con't tell where it is coming from...

bigbillyboy · #4 08-26-2007, 04:02 PM

My front wheel bearings started making noise after I changed out all the ball joints, even repacking didn't make the noise go away. I installed new bearings and problem gone.

also. when my driveshafts started to go bad, a vibration started in the car, and cleared up with new 1/2 shafts.

just thoughts.

Ken300D · #5 08-26-2007, 08:07 PM

A bad wheel bearing will often groan loader when you go around either a left or right curve, or if on a wide clear road, you swerve to one side or the other a bit.

The sound I got from a bad wheel bearing on my 300D was unlike any other bad wheel bearing I've heard before. On other cars, you realize fairly quickly what it is, but the sound on MBs makes you think it could be the tires, transmission, or driveshaft.

But the additional pressure on the bad bearing due to a turn completed the diagnosis for me - and the bearing was clearly bad when I took it out. What it really looked like to me was that the "radio suppression" spring had gone bad or worn out, and was being ground up in the bearing. That new part didn't go back in the hub. I don't care about radio suppression or the brake wear light, I check the brake pads often enough.

Ken300D

spark3542 · #6 08-29-2007, 10:48 AM

I pulled my CD manual up, and it shows a Ujoint next to the center driveshaft bearing, but no discussion of R&Ring this ujoint.

I haven't begun this whole process, but I think I'll pull the driveshaft, replace every wear item there is.

Driveshafts should be a no-brainer, but MB seems to have made this needlessly cumbersome (i.e. Step 1...remove entire exhaust system)!!!

Anything special about this ujoint? I assume a typical press to get it out?

Thanks

Mark

LUVMBDiesels · #7 08-29-2007, 11:14 AM

Quote:

Originally Posted by toomany MBZ

May be the center drive shaft bearing.

I agree with these posts. I had the center bearing go bad on the BMW and it sounded like a growl in the driveway that turned into a whine at road speed. It was highly annoying. If the sound does not change with turning the car, it is probably this bearing.

toomany MBZ · #8 08-29-2007, 01:38 PM

Quote:

Originally Posted by spark3542

I pulled my CD manual up, and it shows a Ujoint next to the center driveshaft bearing, but no discussion of R&Ring this ujoint.

I haven't begun this whole process, but I think I'll pull the driveshaft, replace every wear item there is.

Driveshafts should be a no-brainer, but MB seems to have made this needlessly cumbersome (i.e. Step 1...remove entire exhaust system)!!! There are resonators you may have to deal with otherwise, I don't know about the exhaust, but there is a "tunnel" on my SD partially enclosing the drive shaft.

Anything special about this ujoint? You have to loosen a very large nut, I've read 46mm, or 1 13/16, or some folks have used channel locks, as it's not on there too tight. I assume a typical press to get it out? I think so.

Thanks

Mark

I have not done this, but have read about it, answering the best my memory will allow. I've had the resonators replaced with a straight pipe to muffler on the SD.

estod · #9 08-29-2007, 05:30 PM

I think I read on here that the center U-joint is not replaceable - you have to replace the driveshaft ........