Change Differential Fluid Highly Recommended
 

I just finished changing the differential fluid on a 1989 420 SEL with 218,000 KM (135,000 miles). The old fluid was dark olive green grey colour and it smelled aweful. I highly recommend changing the rear differential oil especially on the older W126 cars. I used a synthetic 75w90, about 1.45 litres.

When I owned BMW's, they recommended changing every 30,000 miles. MB only recommends checking the level on my 300E every 30K.

I replace it every 30K using Mobil 1 75W-90. In fact, I also use Mobil 1 ATF fluid and motor oil.

Differential oil, even synthetic, always seems to be quite stinky.

I wonder if sticking a king-hell powerful magnet to the outside of the differential, and the engine and tranny oil pans would be useful at keeping metal filings out of the gears?

Differential fluid has plenty of sulfur in it, and you know that most compounds of sulfur with other substances are very smelly or stink.

Eric

Gear oil...
 

All gear oil has a certain smell that gives me a headache. :(
It's the one smell from an automobile that I really hate. :mad:

Re: Gear oil...
 

I thought I was just a wimp. Glad to hear someone else hates the stuff.

diff lube change
 

The mechanic @ the MB shop wondered why I would "even bother @ ONLY 120K miles..."

I gave him a couple quarts of 100% synthetic 75W-90, he put in a quart and a half, my wife's commuter mileage went up almost a full 1 mpg with no other changes.

He bought another quart and changed the diff lube in his 560SEC and saw an almost identical rise in his mpg.

He now believes...:rolleyes:

Some where on this site someone posted pictures of inside their differential after running synthetic lube. It was remarkable how clean it was. No yellowing etc.

I recently changed the valve cover gasket on the 300E. This car has 215k miles and all the rockers etc are incredibly clean and fresh looking.

Haasman

STORMINNORMAN

Did you use the scented or un-scented version ? :D

Synthetic Gear Oil
 

It makes sense to change the tranny fluid and Gear oil to synthetic, since they will last a lot longer than motor oil, and will not decompose due to the excessive heat of the engine.

Recommended Synthetic ATF
 

So what is the recommended synthetic atf for 1989 420 SEL?

75W-90 Mobil 1, Valvoline, Redline or any name brand synthetic.

Yep, that gear oil is vile stuff. Once it's on your clothes, the smell just will not come out.
Why does it have to smell so bad? Other oils are not nearly as repulsive.

Bud,

I believe he asked for ATF ... not diff oil-

haasman, right you are!