Differential Fill Plug Hissing on removal.
Thread Starter
Instructor
Joined: Feb 2014
Posts: 123
Likes: 70
Differential Fill Plug Hissing on removal.
Hey guys, I have been tracking down a differential leak in my C5Z. I started getting a gear oil smell after long trips on the highway. I had noticed that the drivers side axle seal was leaking pretty good. So I changed that last weekend with a new AC Delco seal. I drove it this weekend and I could smell diff fluid still. New seal looked pretty dry so I think it is working fine. Today I went under the car and sprayed brake cleaner as the diff housing was pretty dirty. I also decided to check the level in the diff. When I undid the fill plug it started to hiss. I should have checked if it was pressure or vacuum. I guess I will have to drive it some and pull the plug again. I added about 1/2 quart or more of fluid. I am going to jack it back up and check the vent. The leak on the diff seems to be from the drivers side. Anybody had anything like this before. Just trying to knock the last repair item out on this car. The hissing part is making me think that the vent is clogged up and it is pushing fluid out wherever it can.
Racer
Joined: Aug 2019
Posts: 412
Likes: 205
From: Castle Rock, CO.
2021 C6 of the Year Finalist - Modified
Those vents can sometimes get stuck in the closed position. I removed mine with the exception of the base that is pressed into the case. I then attached a hose using a worm clamp with a toggle valve on the other end. I plan to tie this up once I put my car back together.
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
Check the vent. It's a 1-way valve that lets pressure out when hot and then holds a vacuum in the differential when cold. I suppose the idea is that the vacuum will help keep the oil inside the case.
Thread Starter
Instructor
Joined: Feb 2014
Posts: 123
Likes: 70
Well crawled back under the car. Did not look like it had been leaking but only street drove the car a few times this week. Opened the fill plug and it hissed. But I could not feel anything coming out. I did feel the vent and it was stuck. So I cleaned that up with some brake cleaning. It was covered in gear oil so thinking it could have been the problem. I got to drive the car to Charlotte next weekend so we will see how that goes.
