grease contaminated front axle oli (1 Viewer)

[rc51kid]

I opened the fill hole to check my front diff oil and I had a oil come pooring out. Not so concerned about a little over fill. I might have filled it some on a a incline. But what has me concerned is that the oil ( mobile 1 synthetic 30,000 miles) is dark gray. I figure it is contaminated with birfield grease. My birfields are rebuilt about 40,000 ago with all new OEM stuff. Also the grease in the birfield always looks good and not soupy on a zip tie. The wipes are bone dry. So why am I pulling grease past the seals into the diff area? Would over filling the birf joint do this?

I guess I kind of have two basic ideas. Excessive pressure in the birfield pushes grease into the diff. Or the diff is forming a vacuum and pulling grease in. Maybe a clogged vent line?

Also I kind of figure a little moly grease inside the front diff really shouldn't hurt anything. There is still the proper amount of oil in there as well. Do you guys think it will hurt anything?

 

[chap79]

I would check the breather to make sure it is actually functioning. Also at 30k the diff fluid should be changed again. If no fluid is going into the knuckles I would just change the fluid and continue to monitor it. Just give if a check every week or two to see how fast it changes.

 

[mct75]

My fill plug made a sucking noise when I removed it once. Does the breather have a check valve in it or something? I'm ashamed to admit I have no idea where that hose goes.

 

[JohnVee]

My fill plug made a sucking noise when I removed it once. Does the breather have a check valve in it or something? I'm ashamed to admit I have no idea where that hose goes.

If it's stock, there's no hose for the breather, just a short nipple approx 1/2"dia on top of the axle housing. If a hose leaves your housing then somebody extended the breather up - likely to the engine bay.

 

[Kernal]

From the factory FJ/FZJ80's comes with a short section of hose attached to a pipe nipple (screwed into the top of the front axle housing). The hose runs a foot or so upward to a small plastic box thingy (breather assembly) that has a breather vent on top. That breather assembly is known not to work very well and the small pipe nipple that is screwed into the front axle housing can get clogged with grease preventing the system from venting.

The fix is to run a hose from the pipe nipple on top of the axle housing up to the engine bay and zip tie it off somewhere and then add a small filter on the open end of the hose to prevent dust or water from entering. A few people have widened (drilled out) the ID of the small pipe that is screwed into the housing in addition to the above hose extension mod.

 

[ZackR]

I had the same issue you are having and it was caused by a mostly clogged breather. On mine it was actually leaking the birf soup mix out of the breather hose. I extended the breather up into the engine compartment when changing the front diff fluid and will eventually need to do a full birf job. For now I'm going to keep an eye on things and change the fluid more often to monitor (in addition to keeping the moly grease topped up in the birf).

 

[Peru Darrell]

The grease wont hurt the oil or the diff gears(it's like running heavier weight gear oil), But chances are if the grease is getting into the diff, the diff oil is getting into the birfs.
I even saw some guys shoving bananas into their diff on a show about trucking in Africa once. They just kept stuffing dozens of bananas in their diff each day because they didn't have heavy weight oil.

Extend your breather hoses up to the engine bay connected to a cheap fuel filter where you don't have to worry about river crossings or road junk clogging the breathers.

 

[mct75]

They just kept stuffing dozens of bananas in their diff each day

 

[NLScooby]

"We're not falling for the banana in the tailpipe trick...."
Name that movie....

I need to check my breather valves and extensions as well - this is a good reminder....

 

[Tools R Us]

The grease wont hurt the oil or the diff gears(it's like running heavier weight gear oil),

To a point, true, until it becomes too thick. A prime job of the oil is to cool the ring gear, once it becomes too thick, it gets slung away and cant transfer heat from the gear to the housing.

But chances are if the grease is getting into the diff, the diff oil is getting into the birfs.
...

Not necessarily, the knuckles don't have breathers, so it's normal for some grease to migrate into the axle. The front axle gear oil needs to be changed more often than the rear.

 

[rc51kid]

To a point, true, until it becomes too thick. A prime job of the oil is to cool the ring gear, once it becomes too thick, it gets slung away and cant transfer heat from the gear to the housing.



Not necessarily, the knuckles don't have breathers, so it's normal for some grease to migrate into the axle. The front axle gear oil needs to be changed more often than the rear.

Tools good point on the heat. I am going to clean out the breather system (which is extended). I think the little nipple end is removable from he axle housing, right?

I have full synthetic in there now with the idea of longer intervals between changes. but I think I am going to switch back to plain old cheap dino and just change often. I feel better about that anyway incase water or what not gets in there.

 

[Peru Darrell]

To a point, true, until it becomes too thick. A prime job of the oil is to cool the ring gear, once it becomes too thick, it gets slung away and cant transfer heat from the gear to the housing.



Not necessarily, the knuckles don't have breathers, so it's normal for some grease to migrate into the axle. The front axle gear oil needs to be changed more often than the rear.

Ok Tools, You are right, but it would take a lot more grease than the OP described, like nearly a pound. I would hate to see someone cook their ring gear. Maybe I should have given a legal disclaimer??? hahaha

 

[ChaseTruck]

It'll probably take very little moly grease contamination in the gear oil to make it appear to be black. I would think it'll take quite a lot more to significantly change the lubrication properties of the stuff in the pumpkin.

 

[mct75]

FWIW I removed and cleaned out my breather. It is very easy on a FJ80. The nipple unscrews from the axle with a 12mm socket, and there's a 10mm bolt that goes into the frame rail forward of the brake line. In my case, the nipple was clogged and the breather (a curious thing with a hose barb and a spring loaded captive metal cap, not sure of the theory of operation on it) was totally caked in grime. I cleaned it all up and I think I won't have to worry about hissing drain plugs for a while.