Questionable noises from the rear.
 

I am finally getting down to tracing the noise I have been hearing form the new 81 240's rear.
I notice it most a low speed <20 mph and it feels like a rumble that is loudest as you are backed off the throttle and then back on it again. It seems to disappear when under constant load but it also may be blended with the rest of the mech clatter of the car.
I looked at the center carrier bearing and d/shaft ujoint and stuck a screwdriver into them and tried to see if there was any play in them and did not get any appreciable looseness.
I assume I will probably have to remove them to really check. Is this correct?
The driveshaft has no excessive rotary play and the flex discs look ok.
I loosened up the e brakes to eliminate any drag. The rt side adjuster is broken but turned in to the minimum and it rubs a little but that is not the sound.
There is a noticeable clunk at the diff when the clutch is released between shifts so I have drained, flushed and refilled the diff and did not see any obvious metal particles and the fluid while brown was still somewhat clear. Sound still remains.
Axle boots are intact but I have not confirmed that the shafts are ok though I also think they are not the noise.
I will be checking the rear wheel bearings next and hope it is not them as the fix looks involved.
Any help will be appreciated.

To check the center bearing you need to grab the drive shaft and see if it has any movement side to side. You should have a little, but much more than about a 1/2" is too much.

Rear wheel bearings?
 

No excessive side play at the center bearing but when I jacked up the rear and pulled at the top of the tire and pushed at the bottom I was able to to move the wheel about 1/8 inch in a rocking motion top to bottom.
Is this too much movement?
When I spin the wheels I don't feel or hear any grinding but it is unloaded and not under power so I guess it really won't show up then.

Not Bearings?
 

Pumpkin!

You mean the problem is in the diff?
What exactly is worn, what are my options for repair, how much and what damage am I doing by locally driving it and will it get louder before it fails or just suddenly give out?

You might just want to lay off the broccoli and beans...

Sorry... title got me, just couldn't resist. :D

That's a whole other issue.

Compress-ignite - Do you mean it is diff related? Pinion gear? or what?

Time to pull the driveshaft
 

After exhausting all the possibilities for the growling that can be assessed with the car on jackstands and the driveshaft in place I am, at long last, going to pull the DS and really inspect the center bearing , the ujoint and the flex discs on the workbench.
So as far as marking the ds ends to maintain balance, I should put a mark on each shaft end and on the corresponding diff and trans housings?
Other than that is the whole shaft removal straight forward?

We will see what happens but I'm hopeful
 

I finally finished up the driveline inspection and replaced the center carrier and bearing. The original bearing seemed ok and the carrier was untorn but the rubber seemed stretchier than that on the new unit.
Anyway everything went back together fine; I also replaced the rear swaybar links while it was up on stands and tightened up 2 exhaust pipe clamps that had loose bolts.
I just returned from a much too short test drive [from my house to my dads and back, about a 1/2 mile and not out of 2nd gear] so I am reserving judgement on whether my " questionable noise" are gone but it was not immediately noticeable.
I am hopeful.

vibration and noise
 

90 mile test drive today and the new center carrier eliminated the "pulse" nature of the sound but now it is a constant vibration-y growl that increases with speed especially over 45-50 mph
Also it makes the noise in neutral as well as in gear.
After the ride I felt both rear hubs in and out and both were equally warm but not excessively so. The diff also was warm to the touch but not hot.
So forum folks, what is the consensus; wheel bearings, diff, axle[s]?
I had the wheels balanced to eliminate that and I think alignment needs some work/ There still is a slight shake in the car as it runs down the road but I am hoping alignment will cure that.

I also have some noise emanating from my rear end (240D), so I'm finding all this fascinating. My car is just generally noisy, but no vibrations or rumbles so far. I have not even tried to diagnose anything yet. I've never even had my car on jack stands.

Ignorance is bliss; once you crack open one of these MB pandoras boxes you really can't close it and you end up chasing every little thing down.
I think I might try the "syringe full of lube through the axle boot" trick to see if that quiets it down.
These look like original axles and while the boots are intact, things still may be dry inside after all these years and if it works I will know and if not I will have eliminated another component from the equation

when/if the wheel bearings wear enough, you will have some slack in the wheel. jack up car and shake the tire/wheel assy at 12 and 6 oclock, and at 3-9 oclock... you should have some play if the bearings are going...

I think most of these diffs are noisy.

There is some fractional play in the wheel with my hands at 3 and 9 but none at 6 and 12.
When wheel bearings start getting noisy are they nearing the end or are they at the end of their life?