Transfer Case Oil Change

I was changing oil in my transfer case, (Spicer 18), and when I removed the plug to let out the oil it sounded like it was breaking a seal and I could hear what sounded like an air leak. Is this normal for the transfer case to have a vacuum? This is a rebuilt case with 2500 miles on it.

 

Sounds as if the breather is clogged. Remove and blow air through it. Wash out with solvent.

 

Thank you, I'll try that

 

I'd think "hissing" is ok. The breather isn't really designed to let mass amounts of air (i.e., dirt, water...) in.

Now if it were drawing such a vacuum where it was going "glug, glug, glug...", then there might be an issue.

 

how would it create a vacuum? Especially if it shares oil with the tranny, which a lot do.