evb's suggestion sounds reasonable. It would be easy to swap the left & right axles. If the noise goes then you have your answer. Unless some one has a good reason not to go down this path. Fingers crossed that swapping them fixes it!!!

I really appreciate the responses. EVB, did the axle swap fix the noise? The noise was present prior to rebuilt axles and is also present with the rebuilt (CVJ out of Denver) axles. I find it hard to believe that the rebuilt axles would have the exact same issues as my old ones. Stranger things have happened, I guess. I'm taking my Indy for ride to have a listen on Friday. I'll let you all know what he thinks. I know a couple of other good MB mechanics I can go to for a 2nd and 3rd opinion. Would like to avoid throwing further parts at it....

The bearing mystery
 

I had similar noises with my 90 300E and 92 300TE. The 90 300E for months had a little noise, which would go away as soon I stepped on the gas. Finally a different loud noise and my mechanic told me I was the differential. It cost me a bundle and the problem remained the same. Turned out it was the axle as result of a bad bearing. I discovered the problem when the car was on the lift, in drive, and it was very hard to hold one wheel in order for the other to spin. There was so much friction on the bad bearing, which made the wheel hard to turn. Changing the bearing and axle fixed the problem.

The 92 300TE had a different noise, which I was also told it was the differential. I told him to change the bearing. He messed this up also, so I got a spindle for $100.00 from a junkyard (complete wheel with bearing) and the car is fine now. With this car, I did try holding one wheel to see if it was difficult for the other to turn, but this bad bearing wasn’t as bad as the one from the other car. So holding one wheel isn’t a way to trouble shoot bad bearings but it helped me the first time.

Good luck
Michael

Well, I swapped the axles when I was changing differentials, and the noise is not gone, just reduced. But keep in mind I replaced my diff with a used one I found on craigslist. I suppose I could have done a better job of isolating variables on that one...

I look forward to reading what your mechanic has to say. Wheel bearings are next on my list, then new axles. And not to hijack your thread, but do you ever get a howling noise on hard acceleration from a stop?

EVB, my experience with the bearing for the 92 300TE, was that the bearing puller did not work, that’s why I end up getting a spindle from a junkyard. I would need to send it out to a machine shop to press it out. The bearing from Mercedes cost me $200.00. The machine shop would have cost me another at list $100.00, then there is labor. So I was looking all together about $500.00 for a bearing. By bringing the bearing back to the dealer, it only cost me about $250.00 and my wife had the car the next day. On my 90 300E, the bearing had fallen apart, so it came out easier.

Good luck
Michael

In this order...
 

U-joint

Rear hub bearing(s)

Differential input shaft bearing

are the most likely suspects.

Whiskeydan: Are you referring to the ujoint between driveshaft halves?
I have a similar driveline "growl" and the DS ujoint is slightly "notchy" feeling although it moves easily with no binding.
Center carrier and bearing are new and flex discs look and feel solid.
I have been told by other MB owners that this notchiness is not uncommon on our aged beasts and is usually not an issue.

Whiskydan, can U-Joints be repaired? I was under the impression it's extremely difficult with MB. Could rear wheel bearings make a noise that is throttle dependent? Input shaft bearing on diff. seems very possible but most folks seem to recommend just putting in another diff. rather than try to repair, do you concur?

Yes, A notchy center u-joint will make this odd noise under acceleration.
Under load, the diff is torqued upward slightly causing the driveshaft to no longer be straight. During this moment the U-joint is running in the notchy area of it's bearings.

The joint is staked into the yoke and cannot be easily replaced.

I guess one could use a small grinder and remove the old one then re-stake a new joint in place. If one is available...

Whiskeydan, that makes sense. However, my issue seems to happen when there is the least amount of load on the driveshaft, at least above a certain speed. Hard acceleration is very smooth and noise free (as is hard cornering which makes me doubt bearings) and similarly, letting off of the peddle and allowing the engine to slow the car (and load the driveshaft in the process) is also smooth and noise free. It is the in-between condition of small load on the driveshaft that produces the rumbling for me. That suggests to my amature mechanic's brain worn teeth in some part of the differential. I really wish I had had my Indy save some of the diff. fluid for Blackstone. :(

An Update:
 

Went for a ride with my Indy. The noise does not sound like bearings or differential to him. He is leaning towards a drive-shaft issue. I swapped out center support, center bearing, flex disks, trans. mount and driveshaft centering sleeve about 5K miles before I noticed the noise (there are about 8K miles on those parts, now). It's possible I bunged something up or a part has failed prematurely. We'll see. Car goes back to Indy on Friday for further investigation and possible diagnostic drive-shaft swap. I'll update when I know more.

?????

The 1.3 L differential case houses a 210mm gear to take the higher torque loads that a V8 puts out.
The case that's in your car currently is a 1.1 L differential case and has a 185mm gear. It's a much weaker unit.

Combined with your manual trans and driving style, it seems you beat the crap out of your differential, hence the need for a stronger unit.



.

Ya but that won't mount without modifying the body and axles right? You're talking about second gen W126 diff? I have looked at doing it before. It's doable, but not high on my list of things to do.

No I am talking about First Gen w126 or w116 or maybe 107 type differentials with no modification to the axles. You will not get it in the 2.88 flavor, but certainly you can find a 2.47, 2.65, 3.07 or 3.46.

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