OK, this is getting frustrating and I'm HOPING someone can give me a little insight here.

A few months ago, I pulled the stock half shafts out of my car and replaced them with C5 units (cheap insurance). A couple weeks after that, I started noticing a small fluid leak from the driver side of the diff.

I figured I must have nicked the seal somehow during the swap, so I picked up a new seal from the dealer and swapped it in. I was very methodical about getting the seal in correctly and making sure the axle stub went back in carefully....

It still leaked....

OK, MAYBE I got a bad seal from the dealer. I tried one more.

It still leaked...

Now I'm thinking maybe the axle itself is out of spec or something. I picked up another re-manufactured C5 axle and one more new seal (since if the axle WAS the culprit it presumably would have damaged the seal).

After swapping in the SECOND new axle and the THIRD new seal, the diff still refuses to stop marking its territory wherever I park it. I even ran a little bead of permatex along the bottom of the diff side cover where it meets the outer edge of the seal on the off chance the fluid was actually pushing out there.

It's not a serious leak. It seems to lose about 2-3 ounces of fluid every few hundred miles so it's not enough for me to park the car, but I certainly don't want to keep topping off the diff every couple of months.

I thought it might have been blowing fluid out the vent on top of the case, but the fluid stain on the side cover seems to suggest otherwise....



I can't see any fractures in the case and the car has made plenty of hard pulls since the leak started with no adverse effects so I'm fairly sure there's nothing broken.

What I have noticed is that there seems to be a SIGNIFICANT pressure differential inside the case. When removing the half shaft or the fluid fill plug, you can hear a distinct hissing. I would have thought the vent on top was supposed to prevent that.

I know this problem plagued the C5s but I also know the seal was redesigned which was supposed to have largely remedied the issue. Anybody have any ideas? Input would be greatly appreciated!

 

Here's some ideas....

I recall (from C5) that the side covers were not flat where the seal is placed.

Check for flatness/ levelness and the groove for the seal too.

Check that the vent is not clogged or pinched.

With your "hissing" comment, pressure build up is a possibility.

 

My diff has been leaking from the vent since it was pulled and serviced a couple of months back. Its a very very small amout for me as well but mine is definately coming from the vent at the top. After a couple of hundred miles I pulled the plug and noticed a ton of air/pressure being released the more I turned/released the fill plug. When we pulled the diff it was noted there was a ton of fluid all over the diff but nothing was hitting the garage floor. Now, I see a thin 2" puddle on the floor after driving. When I checked the fluid this last time it was still dribbling out so it can't be loosing a lot.

 

Mine is the same way. It'll leak for awhile and I'll check it only to find the fluid still leaking out the fill hole as soon as I open it. It's apparently not losing anywhere NEAR as much fluid as it appears to be.

I'd like to check the vent but unfortunately I can't really get a look at it without dropping the cradle/exhaust/tunnel plate and lowering it a good 6 inches which I don't want to do if I don't absolutely have to. I lowered everything once already when I installed the diff brace on the car after the above photo was taken and I briefly checked to make sure the cap on the vent was loose (ie: wasn't stuck or something). It SEEMED ok.

 

Does anyone even have a pic of this vent at the top?

 

Your vent is plugged and possible you are over full also. Later! Frank

 

Any idea if the vent can be removed from the diff for cleaning without taking the entire back of the car apart?

 

This would explain the pressure relief as we both remove the fill plug, so now the fix?