foam=air between the gears, not oil. that is bad. its some what comon when the oil has got hot and broke down. last time i filled mine i used Richman Gear synthetic fluid, next change will see Redline severe gear oil, its the equivelent of a 50w-250 oil... yes you red that right.. not a typo..

 

See, I agree with you. Foam = Bubbles = Bad. Only time I've seen foamy diff fluid was in diffs that overheated, were overfilled, or were in a Dodge

 

The AAM axles heat up extremely hot during run-in process, that's one of the reasons your not suppose to tow the first 500 miles and the early fluid change out recommendation by DC.

 

all new gears run hot durring break in.. the aam's are diferent from the dana's in the fact they only have .003-.005" back lash vs the dana .007-.012".
the cut of the gear is entirely diferent alowing a much larger contact patern and for the teeth to clide acros the gear face much easyer...
so larger surface area generating heat = more heat to have to disapate, not nesasaraly a bad thing, once broke in theres less friction and les heat.
besides, if your gear oil cant handel a sustained 235 deg get a diferent fluid..

 

Try temperatures over 600*F during run-in for AAM axles.

 

600? realy?
i cant think of a single gear oil, synthetic or not designed to run in this range???
as a fyi, we generaly paint dif covers at work with crylon, it generaly burns off between 250-275, we use it as a tattletale to see if the dif has been overheated durring breakin ...
we also do our own in house r&d..... i;d have to look back but i dont recall ever seeing a diff over 400, even towing durring breakin..

 

Just repeating what was said at a DC training session. By the way crylon is spelled with a K.

 

When I put a mag h pan on the rear dif the factory stuff was all milky looking too. Like the lower unit oil on a boat with a bad seal. Other posts on this site said that was typical of factory fill so I went ahead with install and refilled with mobile 1 syn.

 

This is a great thread. I with I could chime in with some answers. All I can say is that when I first changed my diffs the fluid looked like it has seen better days.

I put the Valvoline synthetic 75-140 in the rear and 75-90 in the front; we’ll see how they look at next change.

 

I had foam in mine today when I put on my MH covers. Only in the rear though, front was fine with 11,*** on the odometer. Probably 10,*** towing 15-18000 pounds.

 

Same here on the foam in the rear and none in the front.

Boris

 

I've seen Lucas oil additive do that in diffs and motor oils.

 

With foam like that and grey oil normally I'd say the cause was water intrusion, but it seems its somewhat normal on these trucks. When I did mine I didn't have any foam, but the oil definitely had a grey tint to it. I figured it was from lubes used during manufacture and assembly.

 

Have you set the backlash differently to require this? I've had good luck with Redline shock-proof and severe duty oils, but always had unique reason to require it. An oil that heavy sure will suck up a lot of power.

garrett

 

A little off topic but I see under bluebulls heading he's been banned, what happened? I've read many of his/her posts and learned alot. Maybe a little ruff around the edges but seemed to know his/her stuff.