I just used Castrol Syntec 75W/90 in my diff - PeachParts Mercedes-Benz Forum

i-osprey · #1 07-09-2009, 03:44 AM

This is in a 1993 W124 300D.

I was supposed to use 85W/90 or SAE 90 according to the manuals but I couldn't find any at the parts stores.

I was actually only looking for 85W/90 and didn't know that I could use SAE 90.

The Castrol is synthetic but I definitely noticed that it was much lighter in color and thinner than what came out.

On my test drive it seemed like the whining I had attributed to the tires had diminished significantly.

I also filled the diff with the car jacked/ramped on the driver side so I probably got a little bit more in there than if it were level.

According to the manual it takes 1.3 liters but adding up what I put in based on the measurements on the side of the bottles I put in about 1.442 give or take a drop....

I also serendipitously learned that the boot for my driver side axle that connects to the diff is torn.

Have I jeopardized my diff with this weight oil?

How big a deal is my boot being torn?

I glanced inside the boot and it looked like the axle was coated in a whitish grease and I didn't see any rust or anything.

However, since the previous owner worked cattle in this car and I have found about a hundred pounds of sandy mud caked in various parts of the car I suspect that there has to be some abrasive material in the boot and on the axle shaft.

WINGAS · #2 07-09-2009, 08:01 AM

You should be fine with the synth oil. I used plain ol dino oil, Lucas brand. I think my 265K diff has too muich backlash, so I keep the stuff dino and on the heavy side.

fruitcakesa · #3 07-09-2009, 08:35 AM

That torn boot is a bad sign. The lube needs to be clean and the boot replaced. Check for noise or binding from that axle.

Oldwolf · #4 07-09-2009, 10:10 AM

I just changed min with Mobil 1 75W/90. You will be perfectly AOK with your choice of Castrol. The boot needs to be replaced to prevent damage to the CV joint from moisture and road dirt.