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?

[Flyingw]

No, just making a point. Bath differentials arent under pressure so a heavy weight oil shouldn't foam up like that. Tomorrow, I'll run one of mine and pull the plug immedietly after so see if mine is that way.

[fordtech90]

You said you rebuild whole rearend including differential..id say you have major overheating? Have it all set up too tight...?

[Flyingw]

That is a good question Ford. It is possible to flip flop ring gear shims on those diffs. If the gear mesh is too tight, that would cause excessive heat. The book says up to .018mm backlash is acceptable.

[djm0242]

No the diff wasn't rebuilt. It was in great shape. Seals bearings axle tubes. No it's not overheating. Good questions :) I was reading that the fluid gets mixed with air and that it is expected to foam some. I just want to be sure that I'm experiencing normal operation. If not I wanna fix it. Flying- if you'll do that for me Id love to know what you find. It seems like the opinions are split some people say it shouldn't foam others say it is inevitable.

[Flyingw]

Roger that. Will do that tomorrow and report back.

[Flyingw]

Ride Report: After taking it around my hood and around my yard a few times, the gear oil was not foaming like cool whip. It had air bubbles in it from being agitated but I expected that. The air bubbles gave the greenish gear oil a white hue but nothing like you described.

[djm0242]

Ok Flying. I really, really appreciate you doing that for me. I'm working on a solution. I've cleaned out the diff. I used some gas and a squeeze bottle and my shop vacc. I put the rear end on jack stands and cranked it up and put it in gear. Got all the old lube out. Then added a little gas left it running and uncapped- add a little gas suck it back out etc. got it clean, clean. I think I may try some 75w80 full synthetic. I read that that stuff is great. Thanks again Flying. Ill let you know what happens.

[Flyingw]

Ya for sure. Its got me wondering whats causing the oil to foam.

[djm0242]

Still baffled- for some reason nobody has any gear lube around here that says "Hypoid" on it. There are GL-4 and GL-5 but even after all the reading and work I've done. I'm just not ready to jump on in with any old kind of lube. I'm guessing I'm headed to the dealership to buy the Honda version or Silkolene I'm ready to ride with out worries!

[djm0242]

Ok I cleaned this rear end out yet again. This time the fluid had a blue hue to it. I must've pumped too much marine grease into the axle tube and I'm guessing that the grease slipped past the seal contaminating the fluid in the diff. So today I bought some actual Honda brand shaft drive 80w90 Hypoid fluid. The fluid is still a little foamy but not nearly as bad. I've decided to run it for a little bit and then ill clean it out again. Hopefully the worst of the contamination is past. To FlyingW and everyone else that has helped with their suggestions I say THANK YOU!

[Flyingw]

You are very welcome. Keep us posted.