Front Differencial Vent

Z71SIERRA · March 9, 2005

Has anyone seen this one. My 2002 Z71 Sierra is leaking differencial fluid from the vent tube on the drivers side front inner fender below the main breaker/fuse box. I was changing my oil when I noticed my 6 month old Bilstein drivers side front shock was covered in oil. I figured "great a blown shock already". But when I checked it out I found fluid had leaked down from the engine compartment. The vent tube runs up from the front differencial an ends below the main fuse box. Why would a differencial blow out oil??? It is not making any noise and the 4wd works fine.

dino688 · March 9, 2005

only reason i could think that oil is coming out of the front diff is that theres too much and the oil comes out the tube since it expands under heat. or possibly you have water in the diff and thats displacing the oil....

sincityZ71 · March 9, 2005

Yep, there is most likely too much fluid in the front diff. Had the same thing happen to me, so I crawled underneath and unscrewed the filler bolt, and sure enough a bunch of oil came draining out. I also did that when the oil was cool as it expands when it is hot, which is why is blows out the vent tube. Made a big mess under the truck, but not as big as my now leaky diff/hub thingy...ugh

asilverblazer · March 9, 2005

Mine does it too. I think it is a combination of heat and excess fluid. I haven't removed the filler bolt to let any drain out. I figure a little too much is better than a little too little, especially since my has a leaky diff/hub thingy...ugh

Butch 02 Denali · March 9, 2005

This is actually a common problem. The vent is broken at the swivel. The old style is plastic, the replacement is metal. There is a TSB on it but I don't have it.

the color of the tube is important too. If I remember correctly, the white tube must be used if the diff fluid is changed to synthetic.

There were quite a few posts about this a few years ago, anyone else have any links or the TSB?

sincityZ71 · March 9, 2005

Mine does it too. I think it is a combination of heat and excess fluid. I haven't removed the filler bolt to let any drain out. I figure a little too much is better than a little too little, especially since my has a leaky diff/hub thingy...ugh

<{POST_SNAPBACK}>

Yeah i keep mine loaded up with gear oil now that is has that lovely slow leak. Glad I am not the only one with that. And I found it is horribly expensive to get fixed...they seem to want to only replace the whole hub assembly instead of just replacing the seals

Z71SIERRA · March 10, 2005

Thanks for the info...especially about the replacement vent. My truck has 38000 mi on it and I've checked the diff fluid level once a year or so ago and it wasn't overfilled (It was right up to the plug) but it didn't make sence that it started blowing lube after 38000 miles now.