Hey, I am wanting to change out the differential oil on my 300SD. It has a rebuilt rear end and was recomended to change the oil out after driving it a month or so. What is the recomended oil to run in there? I would also like to use synthetic? Thank you

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1985 Mercedes Benz 300SD, TMU
2015 Chrysler 200S

Uh ohh...here we go.

I use Mobil 1 Synthetic. I believe it is 75W-90. You will need just over 1 bottle (1.1 or 1.2 I believe is called for by the FSM) so just buy two bottles. A pump makes it easier (though some do it by simply cutting the tip off the bottle on the SDs) and make sure you remove the top FIRST.

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

Ditto 75w-90. My OPINION is to add Lucas oil stabilizer to rear and engine..I am NOT trying to start a debate on oil and additives.

My experience comes from over a million miles on a diesel OTR truck. It had 11 miles on it when i bought it. 1,217,500 when I sold it. No OIL related issues with engine tranny or rears running lucas products.

Thank you for the quick answers!

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1985 Mercedes Benz 300SD, TMU
2015 Chrysler 200S

I guess I should clarify- When I said top, I meant the top of the two bolts on the rear diff. If you pull the bottom one and then can't get the top one out...

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD

playing devil's advocate....

Check this out from "bob is the oil guy".

http://www.bobistheoilguy.com/images/lucas/lucas.htm





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1983 123.133 California
- GreaseCar Veg System

The only synthetic I have ever used in our two 123s (1983 and 1985) has been for the differential: Red Line 75W90 All-Synthetic Formula High-Performance Gear Oil. One quart (just under if I recall) per differential.

Don't know why I ever started using it. Don't really know if it is a great improvement over traditional dino gear oil. No problems over many, many miles.

need to change my rear diff fluid, so I'm trying to find out if my 1982 300SD has a limited slip rear in it. Other than jacking the car up and turning one wheel...any way to tell? are there model numbers stamped on them or any thing else I can look at?

Does it matter that much on the hypoid additive? can I use oil for a LSD in a non LSD diff? i dont want to put the wrong stuff in it.

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-SpecialDelivery
1985 300CD Silver/Blue H&R Suspension (Sold, still cryin over that)
1982 300SD Silver/Blue '85 OM617 (Sold)
1982 300D - Blue/Blue (Sold)

I would not get too carried away with the diff oil. Dino 80/90, semi syn or syn 75/90. The important thing is that you are changing it.

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the sooner you start... the sooner you'll get done If it ain't broke, don't fix it.. Its always simpler to tell the truth...
2007 Honda Accord EX
2007 Honda Accord SE V6
96 C220
97 Explorer - Found Another Home
2000 Honda Accord V6 - Found Another Home
85 300D - Found Another Home
84 300D - Found Another Home
80 300TD - Found Another Home
Previous cars:
96 Caravan
87 Camry
84 Cressida
82 Vanagon
80 Fiesta
78 Nova
Ford Cortina
Opel Kadet
68 Kombi
Contessa

This little fallacy ought to be put to bed for the last time.

The top set screw is aluminum.

Drain the oil from the bottom set screw.

Heat the aluminum housing around the top set screw lightly with a torch...........after the oil is drained.

The screw will unthread without any effort.

Draining the unit prior to removing the top set screw is preferable because the oil won't act as a heat sink.

Every single person repeats the same fallacy..................

Any thoughts on Castrol 85-140 for very hot, hot, hot Florida?

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1983 300D, the "Avocado"
1976 240D, 4-spd the "Pumpkin", SOLD to Pierre
1984 190D, 2.2L, 5-spd, my intro to MBZ diesels, crashed into in 2002

My Ford Powerstroke truck calls for a 140 weight because of towing requirements, but I think that is too thick for our cars. IIRC MB specs a 90 oil regardless of temperature, even in hot places like Florida or even hotter-yet Arizona. Just dump a good synthetic gear oil in there and drive with confidence. I use Lubro Moly GL-5 synthetic hypoid 75w90 in all my Benzes, and I drive anywhere from the Pac NW mountains in January to the desert SW in July with my rigs with no problems.

They are plugs, not setscrews.
If you are wise, you remove the fill plug first.

I have experienced Fill plugs that would not break free with extreme heat and 1300 foot pounds torque.
Several times I have been forced to replace the aluminum rear cover.


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__________________
ASE Master Mechanic
asemastermechanic@juno.com

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

NO..
MB calls for 75W90 Synthetic, not blend or crude.

There is a TSB for the W123/126 changing from blend or crude to 75W90 Synthetic for better performance/durability and lower sound levels.


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That would be impossible, because the screw is aluminum............and it doesn't rust.

Also, 1300 ft.-lb would have stripped the hex flats way before you ever reached that figure. So, I call BS on that statement, unless the cover was steel.

I stand my by advice. Aluminum cannot resist moving with heat............and it doesn't take much of it.