Bubbles/foam in rear diff fluid?

[irv]

I put this in the "latest diff fluid change" thread but thought I'd ask in case some/most don't see it? Is this normal? Sorry, no pics. My truck only tows occasionally and nothing with any severe weight to it. Boat and sleds only since new. Finally got around to doing my rear diff fluid change on my 13 Ram Hemi QC 4x4 today. It is a LSD with 3.55 gear ratio. Out went the factory fill at 79,000 km's (49,000 miles) and in went Pennzoil 75W-140 syn with the FCA friction modifier. The gear oil that came out was quite dark but I have seen worse. Not a lot of silver/streaking but I was also surprised with the amount of foam/bubbles in it? I did a quick 5-7 mile drive before doing it and drained it within 5 minutes after arriving home. Is this normal to see bubbles/foaming? Not a lot but enough to notice it easily.

 

[BHopkins]

Did you overfill? Overfilling is a big no-no for diffs. It will cause foaming. Diffs are designed to work best at the ideal fill level. Do you have an aftermarket diff cover? One of those aluminum covers with all the fins on it? Squarish in shape and perhaps made to increase capacity, instead of the normal factory style that is simply round in shape? If yes, get rid of it and go back to an OEM diff cover. The aftermarket diff covers are notorious for causing foaming. The only design that goes into those things is to make them look cool. https://www.youtube.com/watch?v=9-yG3D3JBRs

 

[CarbonSteel]

All axles create aeration and foam in the oil--no matter what cover is on them, despite the recent suggestion from Gale Banks and others that only flat back covers aerate/over aerate the oil. Gears are turning at 90° to one another and "smashing" the %@#&$ out of the oil. Take a look at how quickly the oil becomes aerated in the video below. He is running a clear cover that more or less duplicates the dimensions and shape of the OEM cover:

 

[zeng]

Quote

The gear oil that came out was quite dark but I have seen worse. Not a lot of silver/streaking but I was also surprised with the amount of foam/bubbles in it? I did a quick 5-7 mile drive before doing it and drained it within 5 minutes after arriving home. Is this normal to see bubbles/foaming? Not a lot but enough to notice it easily.

Foaming is said to be bad for oil life etc . But, 'within 5 minutes after arriving home' ? I would not consider that as abnormal .

 

[oldhp]

Rear difs are pretty tuff. As long as you fill to the factory level with a good synthetic gear lube you should be fine. Some foaming is normal as in the video.

 

[irv]

Thanks guys. Those vids were helpful in letting me know the little bit of foaming I seen was normal. If anything, I may have overfilled it a little as I put the fill hole plug in before all the excess had finished running out? This was the first time doing this to my truck, Bhopkins. Factory fill out, new gear oil in and no aftermarket cover. With the drain (14mm) on these Rams, it sure makes it easier than removing and reinstalling the diff cover.

 

[randomhero439]

Nice video. When drive line components like axles and gearboxes are developed. It is standard process in automotive to make a clear carrier/housing to evaluate oil flow on a bench and compare to CFD models. Different temperatures, speeds, and angles are considered. These clear parts are typically 3D printed and polished, and in some cases they are injection molded.