Rear Differential vacuum?

So I did the mod where you relocate the rear differential breather with hose to higher up on the chassis. What was interesting is that the 2 times I took off the stock breather, (once to measure the fitting and again to change it out later,) a loud hissing noise could be heard as the air sucked into the differential. I thought the stock breather was a 2 way open kind of deal that would equalize the pressure. I know the one I put on the other end of the hose was.

So could this be causing the howling? Mine didn't howl, but I only had 500 miles on it when I modded it.

Just throwin' it out there.

 

No, that's not what's causing the howling. My old 4Runner and my 1st generation Tacoma both did that too even after I replaced the breathers with OEM replacements because they were rusted solid.

 

Without repeating the good advice in fdbyrne's post, as far as I know, the stock breather is a one way valve. It allows gases to exit the differential without letting water in. Over time it gets dust and dirt in it and the components degrade, so the valve tends to become two-way anyway, so many folks relocate it. The vacuum is normal.​

 

OK, good to know. Thanks.