[brinoff]

My 04 CC 4x4 now has 29000 miles on it. I took it in and had all the fluids changed for the 30000 miles service. After a 200 mile trip home from a mountain trip, I found a large (bigger than my open hand) spot of fluid on the driveway under the rear diff. I called to take it back to the dealership. In the meantime it has not leaked again. The dealership tells me that they cannot find a leak nor reproduce the leak. I feel confident it was coming from the rear pinion seal, as the yoke appeared wet when it first happened. When I went in to pick it up, they had left it on the lift for discussion. While everything appeared dry, there was some caked grease and oil on the gas tank in the radius of the pinion and driveshaft yoke. A different mechanic at the shop believed that may be spray from the pinion, (as the ujoints are not serviceable; thus not likely the culprit). They told me that they would replace the pinion seal as a preventive measure. Does this sound reasonable? As the truck has been leak free since I've owned it, I don't want to do any unecessary work on it. Searching the posts on this site has me paranoid about leaks from the rear. Thanks for your time and thoughts.

 

[HudsonValleyTitan]

My 04 CC 4x4 now has 29000 miles on it. I took it in and had all the fluids changed for the 30000 miles service. After a 200 mile trip home from a mountain trip, I found a large (bigger than my open hand) spot of fluid on the driveway under the rear diff. I called to take it back to the dealership. In the meantime it has not leaked again. The dealership tells me that they cannot find a leak nor reproduce the leak. I feel confident it was coming from the rear pinion seal, as the yoke appeared wet when it first happened. When I went in to pick it up, they had left it on the lift for discussion. While everything appeared dry, there was some caked grease and oil on the gas tank in the radius of the pinion and driveshaft yoke. A different mechanic at the shop believed that may be spray from the pinion, (as the ujoints are not serviceable; thus not likely the culprit). They told me that they would replace the pinion seal as a preventive measure. Does this sound reasonable? As the truck has been leak free since I've owned it, I don't want to do any unecessary work on it. Searching the posts on this site has me paranoid about leaks from the rear. Thanks for your time and thoughts.

Make sure it's rear diff lube. If so, you can't miss a leak. Check the axle vent and the drain and fill plugs to be sure their tight.

 

[brinoff]

While it was on the lift everything appeared dry, the whole case as well as the vent. My current thought is to go pick it up and watch to see if it leaks again. On the other hand they already have it, thus removing the hassle of getting another appointment and getting it there before work, a real hassle to be sure.

 

[Yahooligan]

Being that you just had the diff service done, I suspect the tech overfilled the diff. Your drive in the mountains heated it up enough to expand and come out of the vent tube, then leak down onto the pinion, which then flung it around. The remainder then ended up on your driveway. Now that the diff has "burped" the fluid level is low enough that it won't happen again.

 

[HudsonValleyTitan]

Being that you just had the diff service done, I suspect the tech overfilled the diff. Your drive in the mountains heated it up enough to expand and come out of the vent tube, then leak down onto the pinion, which then flung it around. The remainder then ended up on your driveway. Now that the diff has "burped" the fluid level is low enough that it won't happen again.

But he should be able to see where it was leaking from if it was leaking. That crap doesn't just go away like motor oil..and it smells. It doesn't wash off easily either. Anythings possible I guess but...that crap clings to whatever it's on so finding it leaking shuld be easy.

 

[Yahooligan]

But he should be able to see where it was leaking from if it was leaking. That crap doesn't just go away like motor oil..and it smells. It doesn't wash off easily either. Anythings possible I guess but...that crap clings to whatever it's on so finding it leaking shuld be easy.

On the other hand, when have you seen a leak self-fix?

The only other possibility I can think of is the seal is failing but the gear oil only being thin enough to leak when it's hot enough. When it cools off the oil thickens, just like motor oil, and the leak stops. If he sees evidence of a previous leak (crusty diry and oil on the underside of the truck above the pinion) then that would support this theory as well, however I don't know why he wouldn't have seen oil on his driveway before now. Unless the dealer put a different/thinner/wrong viscosity gear oil in the diff which is now making the leak more evident, they shouldn't have done anything to cause the leak or make it worse.

:cheers:

 

[brinoff]

So, would you support bringing it home and just watching for leaks, or let them work on it? Thanks.

 

[Yahooligan]

So, would you support bringing it home and just watching for leaks, or let them work on it? Thanks.

If I were the tech, I would add UV dye to the diff and let you take it home, put another 100-200 miles on it, then bring it back. If there's even the slightest least it will show up under the UV light and make it very obvious where the leak is coming from.

This will save you time since they won't be pulling your pinion seal and/or poking around and it will give the tech a smoking gun if the leak does come back. If there's nothing after another 100-200 miles but 1000 miles down the road you see a leak then that dye will still be in there to locate the source.

I've never been a consumer (or a tech, while I was working as one) that supported "exploratory surgery", it's a waste of time and money. Using a UV dye is a great diagnostic tool when searching for oil or coolant leaks.

 

[brinoff]

Great suggestion! I'll call in the morning with that idea before I go get it. Thank you.