85 300TD thumping drive shaft
 

It sounds like the driveshaft is thumping in the rear at low speeds. What in the world is that?

Perhaps an axle half-shaft? That would be more likely if you hear it more in slow sharp turns to one side or the other. Further along this possibility, take a look at the inner and outer rubber boots on the two axle half-shafts.

Ken300D

Driveshaft?
 

Flex disks might be the first thing to check in the process of elimination, then maybe the driveshaft center bearing/support.

Drive axle CV joints in my experience with many applications will usually reveal themselves as a problem exactly under the conditions KenD describes, when in a turn, the uneven stresses placed on the associated components will give a different sound in one direction rather than the other. Once you determine that the difference is turning related you only have to determine which side and then what component of the particular side! Peice of cake this time of year i.e. the cold, underside filth and the like, but the satisfaction of deducing and correcting the issue will serve to make you a better man!! This last part is complete bull$#*t, but you've got to find the silver lining in everything!!! Good luck, maybe Santa will have some new drive axles under the tree for you!

Then again it could be that some suspension related componentry that is worn/failing and allowing a measure of mis-alignment of drive train components creating the appearence of drivetrain problems!

I'll be out there tomorrow morning s-turning my brains out, trying to figure out when is there a noise. It seems that it is constant, regardless of direction or degrees of turning. The thumping is most audible at slow speeds. I was guessing that at higher speeds the vibration decreases with the improved harmonics... Or perhaps it could be a gremlin or a band of pixies gone bad...

A long shot,,,,,,,,I picked up some thumping that I thought was a wheel bearing or a 1/2 shaft. Turned out to be loose lug nuts on my right front wheel.

Like I say, it is a long shot, but certainly an easy check before you start getting dizzy driving in circles or ripping something apart.

Get some donuts and you'll be OK

JCD

Try to find a place where you can drive parrallel to a wall or some other barrier, maybe along a bridge or in the past I've done many a pass along the backside of a strip mall. If you roll down the window/s you can sometimes hear the sounds that are emitted outside the vehicle better when they reflect off a hard surface. Kind of using a short time period echo to better determine where the sound is and maybe where it's coming from. A couple of passes driving in either direction might help you narrow it down better.

I'd often thought but have not yet tried mounting a microphone near a suspected noise source to pick up the problem sound when your moving. You could use a cheap audio amp from Radio Shack and a mic directional or not held it place with a homebrew magnetic mount. Run the mic wire up into the cabin and listen up! You could then do a run and listen and the change the mic positioning until you make some identifyable progress. Better yet you could use a laptop and a audio program to record and analyze the ambient sounds, a spectum analyzer program would make quick work of it! As an aside, the small piezo-electronic wafers that are used as speaker/annunciators on various electronic devices and toys make excellent audio pickups when mounted to an object, in fact diesel timimg meters use this type of solidstate pickup clamped to the number one injector pipe to get the exact time of delivery signal by sensing the pulse of fuel in the pipe. Here's a picture of one I've got laying around for reference! They also make pretty good acoustic guitar and percussion pick-ups.

low speed thumping
 

When I bought my 123 it had this remarkable thump at low speed but as soon as it got up to about 5 or 6 miles/hr. the sound would disappear. It turned out to be a driveshaft hanger bearing or center bearing. Good luck