Rear Differential Fluid Replacement
 

I just finished the rear differential fluid change on my 300 D with Mobil 1 75-90 and have a few questions/concerns.

1- The color of the fluid that came out was red, like hydrolic fluid, not the coffee color that is mentioned on a search here. The new oil is a clear/light amber color.
2- The fluid that came out had a yellow "head" on it. I had driven the car about five miles to warm up the fluid and shake up any particles that may be in there. The head seemed to me as not right.
3- The fluid that came out STANK. It was not the normal oil/hydrolic fluid smell, it was putrid.

Is there anything I should be worried about? BTW (as if you could not tell by these questions) I am new to the DIY maintenance world and everything that I attempt on this car is my first time (except oil/air filter changes and those were on gas engines).

I just changed mine at a MB tech session.

The stuff that came out was a dark brown, clear but dark. The tech who was wating me do it said it did not look bad for a car with 140k on it. The stuff that I put in was standarf MB diff fluid. It was light amber like you said your's was. I did not smell anything from the old stuff or the new.

Not sure why the old stuff was read and not really sure what you mean by "head". Do you mean foam like the head on a beer? No idea why that would happen either.

The good....you now have the correct fluid in there.

The head was exactly like a pint of Guiness. It was thick and yellow.

I am a bit worried of some kind of 'fungus' causing the foaming and smell.

Thanks for all of the quick replies :)

From your post I take you don't know how long the fluid was in there. It may have been original. Now you've got good stuff in there. This'll flush the remaining nasty clingage out of there next time you change it.

I had the opportunity to smell the fluid when I checked the rear abs sensor on my 87 300e (appx 125,000 miles). It also had a nasty odor. It may have been original. Is there a recommended or customary mileage or time for changing it? Since mine smells I guess it also should be changed.

I don't think there is a published change interval, but I choose to do mine every 30,000 miles. It's cheap and easy.

Steve
'92 300E Sportline 232K

Thanks Steve.

GL-5 gear oil has a very pungent odor from the additives that are required to meet the extreme pressure GL-5 specification. If you spill any on your clothes it is almost impossible to get the smell out. Make sure whatever you use in the axle is GL-5 rated. A 85W-90 viscosity may be called out, but these are not common in North American, and common 80W-90 GL-5 is just fine.

Transmissions and transaxles without hypoid gear sets usually only require a GL-4, but hypoid axles will not last with GL-4.

Most manufacturers consider open differential axles "lubricated for life" other than maybe a break-in change, and only recommend periodic level checks, adding oil as required, however, if the axle is a clutch type limited slip, it is a good idea to change the oil every 30-60K miles to purge the clutch wear debris, and, depending on the gear oil used, clutch type LSDs require a "friction modifier" additive to prevent clutch chatter and this additive degrades with time. A few available axle oils have the additive. Most don't. Using an oil with the friction modifier additive in an open differential will have no effect, but is a waste of money.

If you have an open differential and are a maintenance zealot, changing the axle oil every 60-120K is reasonable and there is no time requirement.

If the oil is foamed up, I wonder if water has entered the axle, which could certainly happen if the car was subject to flood waters, or it may have not been a correct GL-5 rated oil.

Duke