80-90 Hypoid Gear oil foam?

[djm0242]

Can anyone tell me if the 80-90w Hypoid type gear oil is supposed to foam up like cool whip? That's kinda what it looks like inside my rear differential. Is this correct?

[Jason125m]

It looks like that because it is full of mud and water! Change it! They are notorious for getting filled with mud and water.

[djm0242]

No this hasn't been in any water it's new oil.

[Flyingw]

That is not normal. What brand of oil? Have a pic of it foamed up?

[djm0242]

It's Valvoline 80-90w says its good for all limited slip and Hypoid applications. Sorry I cleaned it up the minute I saw it- no pic available. Maybe I need a specific oil??

[Flyingw]

No, gear oil should be non-foaming no matter what the brand. This is a little baffling. How did you find the foaming? Was it after a ride? Was the diff warm from use?

[djm0242]

Well I just rebuilt the rear axle assembly and new bearings, seals, and also installed grease zerks on both tubes. It works great. I have a habit of checking my work so I opened the differential and the new oil had turned into a creamy marangue like foam-gel. So I vacuumed all that out and put new oil in. I ran it down the road and then opened it up and low and behold its the same thing again. Oh and no it wasn't hot at all.

[Flyingw]

What does the oil look like after is been setting for a while?

[djm0242]

Ill check in a bit. I'm sure it will settle back down again.

[Flyingw]

You, know, I cant recall ever checking the oil level right after riding it. I usually check the oil when its been sitting for a bit. I think we need to do some investigating in to this and the properties of hypoid gear oil. Its possible this may be normal.

Any differential experts care to weigh in on this.

[djm0242]

I just asked a friend of mine who's been rebuilding all sorts of machines for over 30 years he used to own Honda of Plano here in north Texas- ill see what he says too.

[Dirtcrasher]

Still sounds wrong to me. Vent tube? Vent tube off or broke off? Rubber boot is perfect? Mating surfaces at the front of the diff perfect?


85's had plenty of water issues; Got better in 86/87 with some changes to all mating surfaces and a small seal on the brake drum rather than the hole drum spinning on a large seal.

All I ever use is 80/90 hypoid gear oil.

[djm0242]

I just went though it all. I even used clear hose on the vent tube so I could monitor the situation better. That's actually what prompted me to check. I could see a little bit in the tube so I opened the diff. Ill get some Silkolene or Honda Hypoid and see if that makes a difference. Oh and by the way. That's a big reason why I installed the zerk fittings on the tubes. I pumped both axle tubes almost full with Marine grease to keep water out. We'll see how that goes as well.

[Flyingw]

Its not a water intrusion issue but an oil issue. Do you know why some hydraulic shocks are charged with nitrogen? The nitrogen keeps the hydraulic fluid from foaming but that fluid is being compressed where the diff oil is a bath. Big difference.

[djm0242]

Hey Flying- not sure what you mean. Are you saying there's oil from somewhere?