Hi, dieseldude,
yes, warm oil will run out better and will take more dirt along. I drove about 25 miles on the Interstate to warm it up.
Your manual should give you the volume required (it was 1.4 quart for a W126) but it should be right at the edge of the filler hole. Once it starts running out, its full.
The intervals for changing are rather long (like 60,000 miles?). My M&R manual doesn't even mention it.
The plugs need to be torqued. Again on a W126 it was 37 ftlbs or 50 NM.
Somebody with a car like yours might know exactly.
There is an alu-ring under the filler plug that should be replaced. Mb will charge you prob. less than a dollar.
Hopefully your plugs are not as tight as mine were.
Good luck
Reinhard Kreutzer

how to change differnetial oil (W124)
 

Ok guys,

I've read through the archives and amassed a bunch of info I want to confirm. I've never change the diff oil in any of my Benz's and want to start (usually my mech. takes care of it.). From what I've gathered, this is not any more difficult than changing the motor oil.

1.) remove drain plug (check that you can remove fill-plug first ;)
2.) drain fliud,
3.) replace drain plug
4.) refill with fresh fliud

One question is - is it beneficial to get the oil hot like with motor-oil changes? How much driving required to do so? What is the recommend intervals for changing diff oil?

Also, any other caveats or tools to make this go as smooth as possible?

TIA,
- Ryan

You may want to get some kind of long hose or pump...
 

to fill the differential with fluid. It is tight room down there.;)

One of the best tips on DIY diff oil changes I received from this site is to remove the filler plug first. If you can't get that one out, you won't want to remove the drain one. Good advice.

Parts stores sell plungers specifically for this job. Usually around $10.

Haasman

Do you have the 14mm allen head socket? Forget an l-shaped allen-head. You'll need leverage.

Auto-Zone sells a set which includes the 14mm; othwewise you get to go see Mr. Snap-On and when I bought mine it was $21 for a single 14mm allen-head and that was 6 years ago.

Above advise about removing top plug first is good. You could be in a mess if you drained and then couldn't refill.

Ah yes, the "14mm allen" .... I found mine at Sears. I think it was $11. Everyone was very surprised they had one in stock.

Also the tip on the O-ring. Don't skip it (new one) or you'll be right back under the car to get rid of the little drips.

Haasman

Thank guys!!!
 

Danke Schon!!! Keep 'em coming!

I'm set with the 14mm allen-head socket, so no worries there. I'll pull on the fill-plug a bit a see if some penetrating oil might be in order...

Also Haasman, this 'plunger' you mention - is that to help with the refilling of fluid or actually removing the fill-plug?

Again - big thanks to all- love this forum! :D

Regards,
- Ryan

I did mine not too long ago. It was a little tight, but if you jack up the body a bit it should go rather smoothly with little problem refilling from the bottle spout.

Good advice from Mike about removing the top plug first. It's the tougher of the two to remove since it's not alway's wet with oil. Teflon tape or NeverSieze should go on these threads for an easy time on the next maintenance.

It is to fill the diff after draining. It is a clear plastic tube with a connector that goes on the end of the diff oil bottle. You can use it to squeeze the new diff oil into the differential. Be sure to check the fit of this "spout" to the differnetial oil bottle.

Hope this clarified.

haasman

It is to fill the diff after draining. It is a clear plastic tube with a connector that goes on the end of the diff oil bottle. You can use it to squeeze the new diff oil into the differential. Be sure to check the fit of this "spout" to the differnetial oil bottle.

Where did you get this? I searched for it for years and finally mickey-moused my own filler tube.

When you buy gear oil in the UK, the container comes with about an 8 inch length of clear plastic tube already attached to the container top. I wish I had saved a couple of them when I lived there. Maybe some of you guys in the UK can send us your discarded filler tubes!;) :D

The maintenance interval is 30Kmi, same as power steering fluid. 14mm, 1/2" hex driver is very helpful. I prefer the Hazet 985-14 to the Snap On equivalent. A cheater bar may be required to brake the plugs free, but as mentioned, 50 Nm (37 lb-ft) is the tightening spec. I have reused my plugs even after they were tightened to 110 Nm and have no leaks. For my non-limited slip differential, I use Valvoline 80w90 or Castrol Hypoy C 80w90 - whichever Wal Mart has. The key is GL-5 and something in a 90 weight. For these diffs MB has never approved any synthetics, if you have LSD they you need the MB special fluid.

I just changed my differential oil recently. From the looks of the oil, it hadn't been changed in a looong time. I got the 14mm allen from AutoZone, only about $8 for the set of 11mm, 14mm and 17mm. I needed a 6" extension between my breaker bar and allen to go around the exhaust. Although as mentioned, synthetic has not been MBZ approved, I used Mobil 1, 75w-90. I managed to just use the tall thin Mobil container to fill the oil. You need to really crush the container to squirt the oil in and then refill the container from your second quart. Takes about 1 1/2 quarts.

glenmore
1991 300CE

IMHO you can get by fine without messy pumps, tubes, etc.
Plastic gear oil bottles will 'squirt' even straight up when you squeeze them, and they have those nice pointy nozzles on them.
Squeeze what you can out of the 1st container, then top off 1st container with oil from the 2nd container, and so on...

Tips:
1) Place jackstands under frame, and let axle drop for best diff access.
2) In the winter, warm up the new gear oil in advance by storing it inside. It will squeeze out much easier and faster warm. You can use the microwave oven if you forget.
3) Teflon tape on the plug threads will make them easy to remove the next time.

Now, if you want a challenge, try refilling a 124 manual tranny...
Best of luck.

Speaking of...
 

I just changed my diff oil and manual tranny is next. Are you hinting you've done that?

Re: Speaking of...
 

Yes. At least on a 124, there is very little space between the wall of the tranny tunnel and the fill hole. I cannot imagine getting any sort of bottle near it.
You could probably fit some tubing onto a salvaged pointy gear oil spout, and squeeze it in that way.
I had a gallon container of Redline MTL, so I used a small hand operated transfer pump. I think it was about $5 for the pump.

BTW, there is not enough room to get a typical hex key socket in there.
Make sure you have the tools needed to remove the fill plug before draining!

Best of luck.