Why would my rear axle vent tube suddenly start blowing gear oil? I have had my Bronco for over a year now and it started leaking last week. What would cause this? Is my axle going to grenade?

 

Perhaps some water was able to get into the diff somehow, and now there is too much fluid in there? Have you recently driven through deep water?

 

I had a Bronco that did the same thing. It was a '83. 8.8 in rear, I think. When I put 33x12.5x15's on it, it would blow about 1/2 quart out the breather hose. After it got down that much, it would stop. I refilled it several times, but it was always a half quart low. I ended up just leaving it that way, no problems.