Hey guys, what are you using for an off the shelf replacement for the synthetic rear differential fluid on an 04 3500 dually? I noticed a wine or ringing and found my rear fluid about 3/4" below the bottom of the plug.

 

Mobil 1 75/90 full synth, or previously I used Valvoline full synth

 

So today I visited the dealer. The fluid part number has changed and it does not include the friction modifier for the limited slip. I bought the friction modifier and passed on their $19 a quart GL-5.

 

I just use the walmart brand.

 

Pretty sure you don't need the LS modifier for our AAM 11.5 axles, they are mechanical helical gear lockers. From the manual: NOTE: Trac-Lok differentials require Limited Slip
Additive in the lubricant. Trac-Rite™ differentials DO NOT require Limited Slip Additive.

It's my understanding we have Trac-rite rear diffs in 3rd Gen.

That being said, it will not hurt the diff to have that in there.

 

Not sure, but I seem to recall the proper fill level on those AAM axles being a half inch or more below the fill plug. I can't remember if the owner's manual has that info, or if you need a shop manual.

 

this is correct, 1/2" below fill hole.. I just replaced my fluid this past weekend.