So, I started pulling everything apart tonight on the 300d for my axle job....when I got the differential cover off...I'm pretty sure I've exposed a mess.

The fluid was really brown and smelled a little burnt. I've read a few posts on here that switching to synthetic will help clean it out...but is there something I can do while I've got the cover off to get rid of some of the sludge? Some kind of cleaning solution...brake cleaner maybe? (making sure it's all out before I refill of course) Or should I just run the synthetic for a few weeks and do a fluid change?

On a separate note...now that I've got the cover off...where the heck are the axle clamps/rings that are inside the differential.

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Looks like your run of the mill old differential to me, nothing too frightening. If there is some actual sludge in the bottom of the housing simply scrape it out and feel free to clean things with a solvent like brake cleaner if you want. Just make sure that you give it plenty of time for any solvents to evaporate before putting it back together.

Your differential lasted over 20 years with gear oil that is not as good as the stuff you can get now. Fill it it up and drive it. If you really want to do something just change it out after a hundred miles or so and you'll get out any remaingin dirt in there. It only takes a quart to fill it up and less than an hour to drain and fill it. If you are going to do that start out with plain old gear oil and then put whatever name brand or sythetic oil during the refill.

Cool.. that takes some worries away...I'll give it a good cleaning tonight and tomorrow and put it back together on Sunday...assuming I can find some decent axles at the Pull a Part tomorrow...otherwise it's gonna be the $129 rebuilts from Advance Auto.

I found the clip for the axle....I think this one has seen better days...no wonder I was getting noise from the rear end...

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Remember to put the axels on the other side of your car in relation to how you find them on a salvage vehicle. To accomplish this you will have to mark at least one of them at the yard.

I'll give a slightly alternate opinion, and that is to not use any solvent inside the differential. You don't want anything that is a thinning agent left over when finished. And the labor to do a cleaning is not worth anything to the functionality of the differential. I would use my hands and a rag to clean out debris from the bottom area of the differential.

The burnt oil smell is a normal characteristic of used gear oil. It just has a strong smell.

If you use the Mobil 1 Synthetic gear oil, it has an effective cleaning agent that will take care of residue removal inside the differential. Let it run for a few thousand miles and then change the oil again.

The maintenance cycle for replacing Mercedes differential oil is supposed to be 30,000 miles a change. This is usually news to people who own American cars, because we are often taught the differential oil never needs to be changed. If you follow the MB maintenance cycle, the differential will likely last the life of the car.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

This is helpful information. I have an 84 300D and my owner's manual specifies Hypoid gear oil SAE 90, 85 W 90. I have seen specs close to this at the auto parts stores buy not exactly the same. I was going to check at the Mercedes dealer for what the manual recommends. Is this not necessary?

Richard

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85 300D 75K Anthracite Grey 0-60 in 13 seconds **For Sale**
84 300D 333K Black (The Velveteen Rabbit) 0-60 in 14 seconds
00 Toyota Sienna 208K (Sold)
15 Subaru Outback 43K
11 Subaru Outback 67K
98 Ford Taurus 100K (Gertie - Was Grandma's - drove it to church and shopping - really) Daughter's car now.
30 Model A Ford 2 Door Sedan (Sold) 0-60 in . . . Never reached 60

take a whiff of the new diff fluid before you put it in.. The synthetic stuff is killer..

( waft if.. don't stick your nose in )

I'd just run some Mobil 1 through it in a couple of short changes. If you see actual sludge built up on the bottom scrap it out.

I'm sure all ours look like that inside. When I did mine the fluid originaly came out pretty clear. I replaced it with M1 and after a year it was black. The last time I did it, it still looked pretty clean so, it will do the job.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Well 80's vintage American cars usualy had one foot in the junkyard at 100k miles.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200