# Leakage from front diff vent tube.



## 70monte (Feb 5, 2008)

I thought there were some posts on here about this but I can't seem to find it. Today I drove the 98 K3500 to work. Because of the snow and ice on the roads, I used the 4x4 the whole way there which was 30 miles. I stopped for gas and noticed some fluid leaking from the front of the truck. I popped the hood and there is diff fluid all over the place around the top of the vent tube. The tube does have the plastic vent in it.

The truck did this before right after I changed the diff fluid for the first time. This was with the truck not in 4x4 but it wasn't as big of a mess as today. The front diff is not overfilled so I don't think its that.

Does anyone know what would cause the fluid to come out the vent hose? Thanks.

Wayne


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## B&B (Nov 4, 2006)

If your positive it's not overfull Wayne, disconnect the vent hose right at the diff and see if you can blow through it. Over years of age the gear oil makes the rubber hose swell internally and creates a restriction. Once the pressure builds up in the diff enough it will forcefully expel any pressure along with some gear oil. Make sure the vent cap isn't restricted either.


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## 70monte (Feb 5, 2008)

B&B,
Thanks for the response. Last year I changed the front diff fluid and filled it until it just started running out the fill hole. I let it run out until it stopped. Later, while driving the truck out of 4x4, it leaked fluid out of the vent tube. I thought maybe it had been overfilled and never added any more fluid. I checked the level and it was a little below the fill hole. At this time, the vent cap was missing on the tube. I bought a vent cap and installed it and it didn't leak again until the other day when I had it in 4x4.

I just found some reference on the internet about a newly designed vent tube connector, the big round plastic piece that the hose connects to. Supposedly the deflector on the inner part of the connector was previously made of plastic and sometimes got stuck upside down which allowed it to hold fluid which in turn then got pushed out the tube when things heated up. 

I went to dealer and looked at the new version and the inner deflector is made of metal and is weighted so that the deflector should always hang down and not allow fluid up into the hose. I ended up buying it in case I decided I needed it after I get a chance to take my old connector out and see what type of shape its in. I know the new connector was also made so the seal would be compatable with synthetic diff oil. The guy at the dealer said that there have been a few newer versions since the one that is on my truck. 

Have you heard of any problems with the old type of connector? I personally have not seen the stock one that is on the truck now so I don't know if it could be causing the problem. I will check the tube itself like you suggested. Hopefully the next few days will be warmer and I can hose off all the fluid and get this checked out. Thanks again.

Wayne


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## B&B (Nov 4, 2006)

The revision to the vent tube connector was actually due to the first design not being compatible with synthetic gear oil vs your issue with oil travailing up the vent hose. 

But it was also changed (as you saw visually) to help avoid that very issue...although it was only a common issue with the later trucks where some were factory filled with synthetic oil for cold climate use, but may help in your case regardless...especially if your running synthetic oil in the diff. 

Easy way to tell the difference externally between the old and new connectors is the revised one should be white in color. You'll likely find your truck has the one which is black color, which would be the earlier design. If that is indeed the case go ahead and swap it to the white one you purchased...along with checking the vent hose for restrictions like we already mentioned. That should solve the issue.


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## 70monte (Feb 5, 2008)

B&B, thanks for the help. My truck does have the black connector so I will change it out with the new white one as well as checking the tube for restrictions. I'm not currently running synthetic in this truck so this problem is not caused from that.

I did however used to run synthetic diff lube in the diffs of my 98 K1500 that has the black connector and I never had a problem with it leaking or coming up the tube. I don't currently run synthetic in it now but it still has the black connector and its never had fluid come up the vent tube.

Now I just need a warmer day and for the snow to melt off of the carport. Thanks again.

Wayne


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## 70monte (Feb 5, 2008)

Well, I got the new vent tube connector installed. The deflector on my old original one was stuck in the sideways position so I can see how diff lube could be flung straight into it and up the tube. The old style deflectors do not freely rotate by themselves like the new one does. It got dark as I finished so I have not drove the truck in 4x4 to see if fluid still goes up and out the tube. The vent tube itself was not plugged up. I'm going to keep my fingers crossed that this is the fix.

Wayne


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## B&B (Nov 4, 2006)

I think you'll discover it's going to work just fine now Wanye so take it easy on those fingers. :salute:


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## 70monte (Feb 5, 2008)

B&B, thanks for the confidence. Now I still need to fix the leaky oil cooler lines and the leaking valve cover gaskets. 

Wayne


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## 70monte (Feb 5, 2008)

It seems like the problem is fixed. I drove the truck about 30 miles to work when it was not in 4x4 and the fluid did not come out like it did last year after I first changed the fluid. I also used the truck in 4x4 out in the pasture last night chasing cows and it did not come out either so hopefully its fixed. Thanks again.

Wayne


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## B&B (Nov 4, 2006)

70monte;745514 said:


> I also used the truck in 4x4 out in the pasture last night chasing cows and it did not come out either so hopefully its fixed. Thanks again.
> 
> Wayne


Knowing that little detail...I hope you don't need to crawl back under it for a while. 

Sounds like its fixed Wayne congrats. :waving:


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## 70monte (Feb 5, 2008)

Unfortunately I do have to crawl back under it because I still need to replace the oil cooler lines. It didn't look like it was too messy under there even though there was cow crap all over the place. They just didn't want to go into the corral so I got to use the 4 wheel drive quite a bit. 

Wayne


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