95 S420, diff. whine, or Rear wheel bearings?

[DanielW]

What would be the most likely cause for wear of this kind?
I had changed all fluids (including the diff) when I purchased it from a MB dealer at about 51,000. Used Mobil 1 synth. gear lube 75W-90, (the best I knew of). All was quiet until about 82,000 when a small whine started at real slow speeds (and at 85 up). I changed that diff grease again yesterday, and found small amount of very small bright metal tiny particles in the drain bucket. I kept everything clean so I could see what was there. The lube was still bright, and smelled just like the new. It was practically clear, (as is the new), but there was enought metal I could collect some with a magnet.
Present mileage= 84,406 and now it's whining badly.

I believe this should be a covered repair since it's still under the Starmark for a few more months.

Dealer had done a "differential re-seal" for the PO at 48,000 under the orig. warrantee. Is this very common?

A few days ago , I had thought it could be a rear wheel bearing? Service writer says they almost never go out unless rim is hit hard---that has not occured. What about CV joints on rear? But the grease seals are unbroken and do not leak. I thought those usually are good unless they loose their grease?

I have an appointment Thursday. Any experiences along these lines would put me in a more comfortable position. Educate me QUICK. Seriously, I would appreciate knowledge from those "in the know" by experience or training

DanielW

[miktvk]

We just had the dif swapped out on our '95 wagon at 142k. Last Sept. started hearing a low-speed, medium-pitch whine, accelerating and decelerating. After 4 months, it could be heard at most all speeds, but you really had to concentrate.

At some point, before we owned the car, and before it reached the 105k at which we bought it, the diff developed a long-term slow leak that no one bothered with. I didn't think much of it either, but it was dripping noticably soon after purchase. Had it looked at while changing the diff mount bushings, they said, 'did you know there was no oil in this diff? Just great. So they topped it off with fresh synthetic, but too late, the damage was done. 32k later, very noisy, out it comes.

Your hunch is probably correct, especially with that entry in the service record. If its bearings, it would be more of a rumbling hum than a whine, if that makes any sense.

[DanielW]

It did turn out to be the differential unit, not wheel bearings or CV joints.
MB dealer is going to honor the Starmark on my 95 S420 and plans to replace the entire center section of the Differential. What he called the "pumkin". Keeping my present CV with axles. Supposed to be a new unit from MB. The only downside at this point is I'm not driving my car. They are even picking up the tab on a rental car. Says it will be there about a week.

I am hoping for my silent runner to return !!

Thanks for the post MIKTVK, that was helpful.

DanielW

[DanielW]

New unit was promised, but it looks like what I got was an "exchange aggregate" ger.-"Tauschaggregat". which had the part numbers ground off the case and an aluminum tag attached to show new part number. 140-350 63 14 and another number "Tiel NR 25 0455"
Perhaps this re-assembling of returned cores with (hopefully?, with new gears and bearings) is as close as can be gotten to a new part, with a 10 year old S class

I took 18 days to complete the repair... My dealer provided a rental-loaner car at no cost. I am really glad that Starmark fixed my car!!

But questions persist:

1. What caused the diff to go bad? I assume that the Prev. Owner allowed the diff to run low on lube. Dealer had re-sealed the diff only a few hundred miles before I purchased the car.

2. 500 miles after I got the car back with the "new" or "rebuilt" differential I decided to drain out the lube and install Mobil 1 synth. 75W-90 gear lube. While everything is very quiet now, I was puzzled to notice that only 500 miles had produced a marked blackening of the lube. I let the lube sit two days in the clean pan and the dark lube settled out at bottom of the pan. A very few bright (tiny mico sized) metal particles could be seen and the blackened lube would follow a strong magnet up into the clear top layer of the lube. That meant that the dark lube contained steel wear, right?
NO particle size stuff at all, and the replacement unit is very quiet.

3. Is that much wear normal during the first few hundred miles ?

4. Should I have left the "factory" lube in longer before changing to Mobil 1 synth. ? Looks like dumping out that blackened early wear lube has to be a good thing, ? Right?

Anyone have informed insight into any of this? I appreciate all posts and readers. thanks,
I have pictures of the lube, but it doesn't show up very well so did not try to post here.

DanielW

[miktvk]

Daniel, I think you are correct on all counts. Same thing happened to your car as ours. Unit was run on no oil for quite a while before leak discovered+fixed, but too late, damage done.

If that was indeed a rebuilt unit then for sure, the gears would have been really tight-producing some amount of fine metal shavings.

I don't think you did anything wrong by replacing the new oil.

I got a used unit from Maryland, w/71k miles on it, no defects. I did put new synthetic in it, so should be good for next 200k+