Hey everyone. I noticed a very small amount of liquid just under the rear driveshaft where it connects to the differential. No spots on the floor or anything, but I look between the driveshaft and differential and it looks a bit shiny like it has some oil in there. I did pull the fill plug, place my finger in there and got it covered in black fluid, so it didn't seem low, but I still kept adding fluid until it poured out (I had a leftover 1/2 quart from doing the front diff and there is still quite a bit in there, so I don't think it took much. I have a pump on it that adds fluid a little bit at a time. Plus I did spill some throughout the whole thing changing the front diff fluid. I have maybe 1/4-1/3 qt left. I can't really tell how much because it is in an bottle that has no clear spot to check how much is left.) just to be on the safe side.

I did notice old oil sludge around where the driveshaft is on the gas tank shield and I was told 2 years ago that it was probably a leak that was repaired by the previous owner. I just had the transmission and rear diff fluids changed today (also with a deep pan and rear diff cover) and the mechanic didn't say anything was wrong (and this mechanic would tell me if anything is wrong right away. He is honest and notices everything, but doesn't tell me I need a repair unless it is actually necessary. He did have to get another deep pan trans filter because the one I got didn't fit correctly and he also had to put additive into the rear diff because it is a G80.).

Do I have a real problem here? Is there a chance that it is residual from somewhere and not a real pinion seal leak? If it is a leak, is there any chance of the seal blowing out and puking the diff fluid all over the place? Maybe I should hit it with the car wash pressure washer again and see what happens? Or maybe that could be the cause of this since I wash the undercarriage of the car after snowstorms to get rid of the salt?

 

I took a cell phone photo of what I am talking about. The spot hasn't grown in size at all over the past 2 or 3 days that I have been tracking it. Please note that the grease on the gas tank shield has been there for a long time and that smudge is from my finger. Is this a real leak or could it be from water, snow or ice getting in between the driveshaft and the differential and mixing with dirt or old oil in there and leaving a stain?

The rest of the area behind the axle (especially behind the left rear wheel) is only wet because I skidded on ice earlier in the driveway, was unable to stop and I hit a snowbank going backwards down a hill outside the garage and the truck went over some of it and left a nice imprint of the rear bumper and trailer hitch in the snow (Oops.).

 

mine leaks @ the same point - its the seal and the mech (used to work for GM as a tech - now owns his own mech/tech shop) told me this is common and not to worry more than making sure the diff fluid is topped up.

the concerning part to me is the "black" fluid, have u changed the fluid in your rear diff ever? if not maybe this would be a good time to do so.

 

It was JUST CHANGED on Monday with a new cover, Lucas 80W-90 and an additive (mechanic said limited slip needs an additive). Last time it was changed before that was under 25-28k miles before that and it was black then and now. So this seal is bad? It seems that it was replaced before we bought it in November 2007. That is why there is sludge around it. How much is it usually to replace this seal? I am still going to wash the undercarriage with the car wash pressure washer and see if I can clean that off to see if it keeps losing fluid. It seems that it isn't losing fluid at a high rate because I only pumped a bit in there until it kept spilling out. Less than 1.3-1.6 quarts on both differentials (I did the front diff myself) and I spilled alot of it in the process trying to get it in there. Is there a vent somewhere in that area? Maybe I overfilled it and it spilled out the vent? The stain just seems frozen like it is in the photo. This just seems really weird. The only thing this car drips is engine oil out the rear main seal. It doesn't lose much (maybe a pint between oil changes), but it drips on the garage floor.

 

I just cleaned that oil off with a paper towel. It does smell a little bit like gear oil, but I honestly can't really tell. I'll have to monitor it for now. It does look a bit wet in between the driveshaft and the differential case, but as I said, there are no drips on the garage floor or visible fluid coming out after I cleaned it. I did check the driveshaft for play and there was none up and down or side to side, so no bad pinion or U-joint. I was able to rotate it a couple degrees until I heard a "click" (probably the park pawl in the transmission since I usually hit the parking brake then shift into park) and then it locked, but that was the only thing.

 

well since u just got it changed there's no worries bout the diff gear oil, the seal isn't "bad" but some fluid is bound to get by it at some points in its life

this isn't something that's gonna crap out your entire diff because of the seal weeping once in a while, you should see the amt thats all over my diff and its holding just fine. keep an eye on the fluid level thats all u really need to worry about. If it gets worse worse where it starts to drip sitting still and puddles, thats the time to start worrying about changing the seal on it.

 

Ok Thank you for the advice. I'll monitor the fluid level and any leaks. During oil changes I will top it up if I don't notice any major leak. If I do, I will start carrying gear oil in the car to make sure it is topped up. If it does get bad, I'll make an appointment to get the seal replaced. The oil I cleaned off this morning has not come back (but the car hasn't moved, so that could be why). I also just took a roundtrip 35-40 miles each way and I can't really see any more fluid building up.

Maybe this could be just a fluke somehow? The other night I was on ice and the car wheel hopped twice for a couple seconds each during a skid. Maybe the seal moved a bit and let some oil out in the vibration then reset itself?

 

So much for good news. I just drove 125 miles and not only is the leak back, it is worse. Now there is a line of fluid on the bottom of the differential case. Looks like I am going to have to have the seal replaced. I am not able to crawl under this truck in snow and refill the differential outdoors (no garage at my apartment near college). How much is it usually to replace this seal? Thanks.

 

sorry - cant help you there but maybe just call around and ask the local shops how much to replace the diff to drive shaft seal. plus keep in mind everywhere's different for standard shop rate pricing, so what may cost you $60/hr for labour could cost me $100/hr. this of course throws the entire cost range alllll over.

 

Ok, I called the shop that is installing my Posi-Lok system this Friday and they are going to replace the pinion seal in the same visit. It is a 4x4 shop, so they specialize in both of those. As far as I can tell it still isn't dripping, but a line of fluid is growing on the outside of the differential case only when I drive it. I don't believe it is in need of more fluid yet, but hopefully the temperature will get above 20 degrees so I can get under there in the snow and top it off. It is 0 now and it is supposed to get to -12 to -16 tomorrow night in Upstate NY. During the day it is not supposed to get into the 20s until Tuesday. I will DEFINITELY top it off then. Could all these days with extreme cold temperatures have anything to do with this seal leaking?