Rear differential fluid all foamy?
 

I decided to change my rear diff fluid today and when I pulled the cover I got this:
https://www.dieseltruckresource.com/..._diff_foam.jpg
The truck was sitting for over 12 hours at this point, so it was stone cold. I have pulled open many-a-differential and I've never seen foam this bad, even on a diff that was overfilled. Anyone else notice this when they changed their fluid?

Oh, and I checked my backlash and gear pattern and it all looks OK, although not perfect. I'm wondering if my vibration "issue" is actually frothing my diff fluid!

Normal.What you can see of fliud it looks good.Seen a LOT like that over years.Don't know why.It may not have any more foam then it does now after being driven.Looks like fliud has lots cling which is a good thing.Need a real fliud expert to say why the foamy look but I've seen many like that.

What brand of fluid?

The fluid from the factory was like that in mine as well.Both axles.It was actually worse after driveing it to the shop.It's normal for the factory stuff to be that way.Put some good synthetic in it & have a drink when you're done.[coffee]

Just Changed Mine With 7,000 Miles Looked Like Grey Paint That You Would Use On A Navy Ship. Is That Normal For A New Truck? put On A Diff. Cover With Drain Plug.

No!!!!!!!!!

I filled it up with Redline 75W90 so I'm hoping it keeps that foam down...

Normal I'd say. Lucus is suppose to be bad at it.

Looks normal. just did mine about 1000 miles ago (16k on truck) and it also sat for a while and had the same foam stuff. Must be something with the factory fluid.

Mine was foamy like that too. I had 20k on the clock when I changed mine. I went with Mobil1 75w140 synthetic.

Hub

Not for sure about the foam if it's normal but the ones I have changed and seen changed all looked like crap. So I would call it normal.

The could tell you why the color is gray but then I'd be challenged and have to obtain affidavites to confirm everything for some of the people on here so I'll just say that's the color from manufacturing reasons for AAM axles.

Anything to do with setting up the gears??? If so, I think I know what you are reffering to. [coffee]

When I changed mine out at 10K I never saw any foam on my gears like in the photo. The back axel oil was all gray but the front was gray with a slight yellow tint to it. And as for the Lucas oil I used that stuff mixed in with hub oil on semi trailers and never saw it foam up over many thousands of miles of use.

You hit the nail on the head.

Speaking of setting up gears... Just for kicks I patterned the rear gearset. Here were the results

https://www.dieseltruckresource.com/...r_pattern2.jpg

https://www.dieseltruckresource.com/...r_pattern1.jpg