Front Differential Is Leaking From The Breather Plug

[Demo13723]

so I recently picked up an 85 4x4 and knew she'd need a little love, it's my daily so I try to keep her as mechanically sound as I can, doing all the work in my off time. First issue I noticed was that the front differential was leaking. At first glance and brief study I thought the rack and pinion seal could be the problem after observing the oil buildup in the area. I changed that out and assumed all was well. This morning I saw the small puddle under the diff and noticed the breather plug was bubbling and that it was the source of the leak. First thought is maybe it was overfilled with oil, next is maybe it was the source to begin with which brings me to my overall question, how do I fix it and stop the leak?
Gears are 4:88 and the truck was on level ground when the oil was filled to the bottom of the fill hole, it oozed out prior to putting the bolt back in.

 

[tbplus10]

Ok, properly serviced this shouldn't happen.
And the breather in correct working order should prevent fluid from coming out any other seals or holes via over pressurization.
This leaves the question of why is your axle building enough internal pressure to force fluid out the breather which is designed to expel vapor or gas, not fluid.
I see you serviced the unit, did you drain/flush it to ensure no water contamination? Water contamination would create steam easily, and in turn over pressurize the system and force out fluid.

 

[Demo13723]

I let it drain from the seal but not from the drain plug so that could very well be the issue. Just curious though wouldn't the water contamination eventually resolve itself through the breather?

 

[tbplus10]

Not always, temp creates steam, steam gathers at top areas of case, some may escape, but majority condenses on inside of case then flows downward as moisture to repeat this pattern all over again.

 

[jazz]

I let it drain from the seal but not from the drain plug so that could very well be the issue. Just curious though wouldn't the water contamination eventually resolve itself through the breather?

If there is water in diff it will always settle to bottom. As with boat motors we pull the plug on bottom end after engine has sat a few days and clear water will come out first as it will separate from the oil over time. Draining immediately after use the liquid would be milky in colour. Is your breather plugged? If so it could build pressure and leak.
I check my rear diff annually as it gets under water frequently during fishing season.

 

[tbplus10]

Jazz you make a good point with getting water in the diff during boat launch/recovery.
I had this problem on the axle of another truck a few years back, every time I put the boat in the axle seals would leak and allow water in, then one day I found a 3' receiver hitch extention made just for use while launching, haven't had the issue on any trucks since then.

 

[rickc5]

My suspension shop noticed that the front diff vent on my '83 was also leaking gear oil and they recommended replacing it rather than messing with it. However, I will be draining and refilling the differential before I replace the vent. Heck, a new vent/breather costs less than $10.

 

[rickc5]

I finally got all the gear oil replaced in the diffs, tranny & xfer case. Filthy job, but it was needed--except for the tranny--as it had some newer oil. The stuff in the diffs was black and thick like honey--nasty stuff. Put some Mobil1 full synthetic oil in the tranny & now it shifts better. Expensive, but seems to be worth it.

While buying new breather vents, I found lots of kits for relocating the vents to a higher location so you can ford deeper water. Just sayin', in case you might want to do that.

 

[toyotafan]

Any updates from the OP @Demo13723