Was working under my '92 318 4x4 yesterday to drop the gas tank and noticed a patch of oil on the side of the tank which lined up with another patch of oil on the underside of the bed. Both of these patches of oil were in line with the input on my rear differential. Looks like the pinion is flinging oil around the underside of my truck.

The differential itself has no oil collecting on or around it, aboslutely none. I had replaced the oil in it probably about 2 months ago. The fluid level is normal and I've not been noticing any sort of strange noise/vibration from the rear end.

The patches of oil were more like light a staining, when I touched it I could not smear it, nor could I feel or smell any residue between my fingers. So there is not that much there. But I have no doubt of where it is coming from. Also I haven't noticed any indicative puddles on the ground after its been parked for a long while.

I've heard of overfilled differentials doing this before, although I don't think thats whats going on here. Should I be concerened?

 

maybe a issue from years gone by and was addressed by PO , unless you are the original owner. i would not be concerned since no sign of fresh oil.

 

Just sounds like a leaking seal.

 

Im the only owner of this truck, we'll my father being the only previous and this repair had not ever been done to my knowledge. Should I be worried? Should I bother fixing it if my fluid level stays nominal? I'm going to be doing U-joint replacements soon, sould I plan on replacing the seal with them?

 

the seal is cheap and its pretty easy I would; that seal is 20 yo....

 

Have you recently greased your u joints? When I did that it flung some grease around and did what youre saying.

 

Another thing it could be is if the truck was left parked for several months and never run then the seal could have dried up and shrank. After the truck is drove awhile the seal will g t wet with oil and swell back out to stop the leak. I bought a z71 from my dad a few years ago and it had sit for 6-8 months and was never started. Once i put the new battery in and started to driveit I noticed a trans lea km and also a rear diff leak. I topped the fluids of and drovethe truck for about a week and both the trans and diff stopped leaking. If you are changing the u-joints I would definitely change the seal just to be on the safe side