rare front differential oil leak

[vidvis]

This one has me stumped - I have an 03 H2 with 66k miles - never been offroad. I replaced the front diff. oil seals about 6k miles ago when I noticed they were leaking (oil running down the case and output shaft flanges). I also replaced both half shafts at the same time as the boots were torn /and/ or they were noisy.

Everything was fine until a couple weeks ago. I am now seeing what looks, feels and smells like the front diff. oil appearing on the seam where the drivers side output flange meets the half shaft flange. As I drive, that oil is then flung onto the undercarriage in that area. I repeatedly checked the front diff. oil level and it is full.

I pulled the flanges apart the other day and found a small amout of oil in the space between, with no obvious sign where it came from. The output shaft flange (inboard side that faces differential is perfectly clean, i.e. no evidence of oil leaking from the seal and leaving an oil stain as it runs down the flange.

Only the outside perimiter of the flange shows oil (see pics). The end cap of the half shaft (concealed when flanges bolted together) is intact and seems fine and I wouldn't expect the grease inside it to resemble diff. oil anyway. How is oil getting in between these flanges? I have looked and looked and can't see oil anywhere else from above that would be dripping down onto the flange. Could there be a pinhole in output shaft and oil is traveling through it? I thought the shaft was solid.

I am open for any help or suggestions.

I will post a couple pics once I figure out how to insert them.

[vidvis]

I should add this only leaks after being driven - never after I park it and clean it up and check it later

[IRA51]

Take out the fill plug and get a sample of the diff fluid ,than see if it matchs the stuff that has leaked .if it is the same use lots of brakekleen and clean every thing than go for a very short drive and you should see where it's comeing from.

[vidvis]

I have done that IRA51 - about 6 times in the last couple weeks. I have little doubt I am looking at gear oil. I spray the whole area down with brake parts cleaner after each inspection to clean it all up, let it dry over night, inspect the next morning to ensure it is still clean, then drive it a short distance. When I get back home again, I get the results shown in the pics along with traces of oil splattered onto the frame in that area.

I was hoping this would be something simple like a leaking vent tube or a drip from something else, but can't find the source.

If it is leaking from the seal, the complete lack of any trace of oil on the face of the flange, as would be expected as it leaked from the seal and ran down, and only seeing oil on the outside perimeter has got me baffled.

[HUMTECH]

Take the halfshaft bolts out, drop the halfshaft. Remove output shaft from differential and coat the splines in thread sealer(pipe dope). Fluid is likely leaking past the splines on the output shaft. Just remove the nut on the output shaft and the output shaft will tap out with A small hammer.

[vidvis]

I thought about that Humtech, but again, there is no trace whatsoever of diff. oil getting past the shaft seal. I thoroughly hose everything down with parts cleaner before taking it out for another drive. The only traces of oil is on the perimeter of the flanges near the bolts - no sign of it running down the face of the flange or along the stub of the shaft or anything like that nor is there any trace of an oil leak anywhere on the diff. case

Yesterday I unbolted the half shaft from the output shaft again, and again found a small amount of oil in the space between the flanges as well as on the perimeter of where the flanges come together. I cleaned it all up and then applied a small amount of gasket sealer to the flange faces and bolted them back together.

I later drove about 60 miles on 3 seperate trips between city and highway and inspected for oil each time. No trace of oil anywhere whatsoever.

I have yet to unbolt the flanges and see if there is oil built up in the space I sealed.

Humtech, if I find oil in there, what would that mean? I thought the output shafts were solid. As for the half shaft, it does have an end cap pressed into it on the flange end that bolts to the output shaft, but it seems solid and I can't imagine something exactly resembling the clean gear oil I changed not that long ago coming from a half shaft.

[vidvis]

Humtech, I forgot to add, there is no bolt on my drivers side output shaft (or passenger either). Once the halfshaft is out of the way on the DS, the output shaft can just be tapped out. Is my output shaft different from what you have seen before???

[HUMTECH]

My bad, I was thinking about an h-1 diff where there is A nut holding the stub axle in. I will have A look at one tomorrow if I get A chance to try and figure out where that oil can be coming from.

[vidvis]

Thanks for the info. Humtech. Yesterday I separated the half shaft flange from the output shaft flange that I had previously reassembled with gasket sealer in addition to the bolts of course. I drove it around plenty after having let the sealer set up. When I opened it up, I found a small amount of what appeared to be gear oil inside the sealed area. However, I don't think it is was gear oil at this point.

The flange of the half shaft has a lid or cap pressed into it. I presume that make it easier to access if someone wants to rebuild it later. The oil appeared to be leaking from an area where the cap is pressed in. I am guessing that grease inside the CV joint area of the half shaft gets a bit runny when warm. I always thought the lube inside a CV joint would be a heavy grease that doesn't get that liquidity. By the way, the CV joint never got to feeling any warmer than the other one, and it is not making unusual noises or have any abnormal play in it either.

I cleaned everything back up, and again used gasket sealer prior to assembling it all and have no more leaking issues.

Would you replaced the half shaft or just leave things as is? Is was a replacement product from Napa, is about a year old, and only has 6k-8k miles on it.

[IRA51]

That is why I said to make sure both the diff fluid and your leak was the same ,glad you found it . ;)

[vidvis]

Ira - you were right. Geez, I've been working on my own vehicles for 30 years and even when I go back and compare the two substances, it is still hard to tell the two fluids apart. If not for seeing the oil/liquified grease seep out from the halfshaft end cap, I would still be looking for the cause.

The halfshaft was still under warranty and has already been returned and replaced with a new one.

[IRA51]

The way I check the diff is to put a bit on a paper towel of each and look at the color and see how it spread and than smell them both ,most of the time you can see right away if they are the same . you don't expect a new part to be defective.;)