Rear Axle Oil Change - Does car need to be Horizontal?
 

Don't mean to bore you with an already covered topic here, but my question is in relation to the car position when doing this task.

About to change the Rear differential oil and read most of what is posted here and 90% of lists state to lift the back of the car up on jack stands or ramps... but yet doesn't the car have to be horizontal when checking and/or replacing the oil? How do you get the proper amount of oil replaced if the car is lifted from one side an an angle? Or does this lift make negligible difference?

Of course keep in mind that I have two ramps and can lift the car's rear but don't necessarily want to go out and buy jack stands to left the front end and won't feel so safe doing so especially I have to give it some push to remove the filler/drain plugs... any thought on this?

Thanks for any feedback.

Joseph_H

Since the oil drain is at the bottom of the differential, I don't believe being absolutely level is that critical.

Filling is done by the upper hole and full is determined by when the fluid starts to spill out or by measurement of the amount of fluid.

Tip: Don't drain until you have removed the upper bolt- If you can't fill it, don't drain it.

Haasman

I think you only have to lift the back of the car to help REFILL the differential. No ramps - the differential doesn't need to be lifted. Lifting the car above the differential gives more room for refilling, since most of us don't have the special tool to pump gear oil up into the fill hole.

I think that the owners' manual calls for a specific amount of oil in the diff. so level really shouldn't matter.

Dear Joseph_H:

Please take a look at the attached picture I've just drawn, and you will see why filling up the differential unit with gear oil when your MB car's rear is lifted up is actually better than filling it up when the car is at horizontal level.

Gear oil lubricates the differential innards by the splash method, and it has very powerful anti-foaming additives to counter the oil foaming due to splashing, so overfilling a differential unit is OK (actually it's good IMHO). However, what I'm talking about only applies for MB cars, because overfilling final drive units on some other car models (some Ford ones) is actually bad.

Be sure to use only gear oil with API GL5 75W-90 or 80W-90 on your Mercedes cars. 80W-140 is too thick and should only be used in racing cars, SUVs or trucks. Differential units on most MB cars accommodate about 1.1 - 1.4 quarts, depending on models.

Best regards,

Eric

Great diagram Eric!
 

Thanks all for your feedback.

W108/109, 110, 111, 113, and others with a swing axle rear end MUST be filled with the axles level (car can be elevated) or the left side will fill, holding about 3 quarts of lube. Diff will be SERIOUSLY overfilled when the axle is again level, causing foaming and leakage out the left wheel bearing.

Not a problem on the later models.

Peter