The tighter the clearances, the lower the oil viscosity required to allow sufficient lubrication and cooling at the bearing surfaces.

The higher the viscosity, the greater the power required to move the oil.

Higher viscosity oil has more resistance to "squishing out" of an area and therefore can help quiet noise from pitted bearings. Bearing noise is generally "rumbly" compared to the whine that can be caused by ring and pinion interaction.

Gear oil additives don't get depleted under normal use. Unless it has been overheated or has water or metal contamination, gear oil is generally good for hundreds of thousands of miles.

The numbers are not always what they seem. Use the viscosity specified by MB.

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CENSORED due to not family friendly words

Hmmm.......

I've always heard that sawdust was the best way to make the rear differntial quieter.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Nah, bananas is where its at.
Africa's Cowboy Capitalists (Full Length) - YouTube

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CENSORED due to not family friendly words

It works, but DO NOT open the gearbox after the banana trick. Pheeeew!

I have a 1991 300SE and I changed the differential fluid to a synthetic grade that Walmart sold as gear oil. Drives OK in city but as soon as I drove it high speeds for 40 miles there was a howling so bad I thought the rear wheel bearing was going out. This happened every time I drove it on the interstate.

So I went to the dealer and got their last liter of special Hypoid gear oil and changed it. What do you know, no more mowling and its spec. So in some cases it does pay to use MB Fluids.

Kris, I also seem to recall a 100,000 interval. Let me go check my owner's manual.

**EDIT** My 1972 Maintenance Manual says to do the job at the "1st and 2nd maintenance jobs". Is something that old even applicable to our cars? And what are the first & second maintenance jobs?

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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

I serviced a jeep for my brother that his friend bought on a lot... it was packed SOLID with axle grease... took the rear cover off and it was like a jello mold of the rear cover...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I heard that the best way to keep the diff quiet is to not drive the car... the diff's dead quiet then.

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"Senior Luna, your sense of humor is still loco... but we love it, anyway." -rickymay ____ "Your sense of humor is still loco... " -MBeige ____ "Señor Luna, your sense of humor is quite järjetön" -Delibes

1982 300SD -- 211k, Texas car, tranny issues ____ 1979 240D 4-speed 234k -- turbo and tuned IP, third world taxi hot rod

2 Samuel 12:13: "David said to Nathan, “I have sinned against the Lord.” And Nathan said to David, “The Lord also has put away your sin; you shall not die."

My father used to work for a small car lot, and they would sometimes pack the diff with ...


wait for it...



um...





hamburger...



forget the banana's smell, P fricking ewwww!!!!

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Well:
Multivis 5W40 wont gum up in the winter so bad.
Hypoid 85W90 may get quite thick in the winter.
Transmission Fluid probably too thin to provide good coverage and non-compressability is not an advantageous property.

When the gears turn, as there is no actual pump, the oil must be thick enough to adhere to the gears so that all round lubrication coverage is achieved. I don't think Tranny fluid is optimum for this application.

Just my opinion.

The oil that came out of my diff was about the viscosity of 30W oil so I put in Multivis 5W40 oil. There is enough oil mass in the diff if it is filled to overflowing at the fill port to handle most lubrication needs. No weird noises from the rear end.

Years ago, I had a Toyota transmission rebuilt. The rebuilders put hypoid in it when the manual called for 30W. The transmission ATE itself just after the warranty expired.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)

Yep. The bearings will be burned up from lack of oil. Many modern manual transmissions use ATF which is about a 10 wt base oil. 90 wt will burn those up fairly quickly.

ATF is missing the extreme pressure lubricant added to gear oil. A hypoid ring and pinion slides as it meshes so that ep lube is very important. ATF could allow a fair amount of wear in a ring and pinion if the vehicle is used hard.

I remember quite a few years ago a viscosity demonstration at a repair shop.

There were two demonstrator devices.

One had lower viscosity thin oil like ATF. You'd turn the crank and watch the gears turn - I think there were three. The lower gear was about half in the oil and the two top gears were dry. No matter how fast you turned the crank, you couldn't get the top gears wet.

The other demonstrator had hypoid gear oil in it. It used standard and not hypoid gears though. When you turned the crank, the larger lower gear spun and picked up the thicker oil that adhered to the gear. When the larger gear meshed with the gear above, the oil transferred to it and on up to the highest gear till all were coated with oil.

Very effective demonstration of viscosity and lubrication method.

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)

Hmm I wonder if this would help my 190E's howling out...hm

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Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

I use heavier gear oil,because I drag race,and will soon tow a trailer.Small trailer pop up 1500 pounds

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1999 w140, quit voting to old, and to old to fight, a god damned veteran