Allright, let's see what we come up with. We drove from Florida up the Alaskan Highway in my 83 300TDT this summer, no problem other than an annoying metallic thumping problem from the rear driver side. When I checked the rear end the passenger side half shaft had leaked all the fluid so i replaced it on the road with an after market halfshaft, I actually replaced both sides for safety. On return trip back to Florida the sound began to reoccur. Everything I have seen published say either Wheel Bearings or Pinion Gear. The sound goes with the rotation of tire, is metallic, but is not always present. Could it be the U-Joint hitting the frame from an overloaded vehicle? Or is it the rear wheel bearing, which I shoul have replaced when I did the halfshaft. Or is it the U joint, which has no significant play in it. Ideas, comments?????

Rear wheel bearings generally get noisy (hum or if really getting bad, growl. Thumping is not characteristic of a bearing, although, I suppose anything is possible. Pinion is not likely as it is usually turning 3 to 4 times faster than the wheels (depends on final drive ratio) and failure mode for that component is generally a pronounced whine or hum. (check backlash). If you have any rubber coupling discs in that rear end, they would be suspect. If you have replaced both half shafts, then I would look at the rear end suspension components. Possibly the carrier bushings and any other locating components in the rear end. U-joints should never normally make contact with the frame as the nest (center section) is bolted to the frame. Start at the outermost parts of the suspension and work inward. You have more than one u-joint in that car. With independent rear suspension, there are at least 5 variable geometry drive components you should check, be they u joints, cv joints or rubber couplings. Depends on car and model. A rythmic metallic thumping sound like something worn or out of balance. Hope this helps... ;)

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Jeff L
1987 300e
1989 300e

[This message has been edited by jeffsr (edited 01-24-2000).]

How about a bubble in one of the belts of the tires? I have seen this more than once.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Actually, the tires have been replaced so I'm going to try looking into the variable geometry parts that Jeff mentioned instead of the bearings. May be a flex disc or such. I will try raising the rear suspension manually by adjusting the hydraulic suspension linkage to see if the sound goes away if I raise the vehicle. If it does, it must be drive axle related instead of bearings. What do you think Benzmac.

Could it be the parking brake?

David

actually i had the same problem....found to be the parking brake springs.renew the parking brake with the springs ....should do the trick

I have to say, the parking brake springs in my car drove me nuts till I figured out where the noise was coming from...