Differential venting. Maybe?
Thread Starter
Racer
Joined: Nov 2005
Posts: 404
Likes: 0
From: KY
Differential venting. Maybe?
I just recently started noticing that my rear end is leaking fluid. There are three small spots in my garage(rather small so it can't be a big leak). Here's the weird part. I've been trying to monitor it over the past week or so and I can't get it to leak. Every time I park it I put some cardboard under there to try to catch it. I've let it sit for a few days(no leak), I've run it hard(no leak), I've cruised gently(no leak). I haven't been able to get under the car for a full inspection yet, but I have laid down behind it so I could reach up to the differential to see if there was fluid trickling down. I found small traces that appeared to be coming from the driver's side. After searching the forum I read about the rear end venting fluid under heated conditions. Even though it has been incredibly hot lately this is still news to me.
Does anybody think this is the case for me or are one or more of my seals breaking down. My car is an 04 with 6100 miles and even though that is a pathetic amount of miles the car has not sat for long periods of time without being driven at least a little bit.
Does anybody think this is the case for me or are one or more of my seals breaking down. My car is an 04 with 6100 miles and even though that is a pathetic amount of miles the car has not sat for long periods of time without being driven at least a little bit.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Heres what you do. Jack the car up on 4 jack stands or get it on a lift. MAKE SURE ITS LEVEL! Remove the fill plug. When you remove the plug, you should hear a slight IN RUSH of air. The Diff runs under a slight vacuum when it's cold which helps the seals seal in a static condition. If you dont hear the vacuum, the vent could be allowing air into the diff. When the differential is hot the vent allows any built up pressure to escape. If the diff is overfilled, it could come out of the vent with the air.
Once the fill plug is removed, allow any EXCESS oil that is ABOVE the bottom of the fill hole to drain out. The correct fill mark is oil even with the bottom of the fill port. If it is over full, the leakage condition could be caused by the overfill condition.
BC
Once the fill plug is removed, allow any EXCESS oil that is ABOVE the bottom of the fill hole to drain out. The correct fill mark is oil even with the bottom of the fill port. If it is over full, the leakage condition could be caused by the overfill condition.
BC
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
The vent is located on the drivers side on top of the housing. The small metal cap houses a ball , a spring and a seat. See if you can spray some cleaner in it. If you have a damaged seal, that will also allow the air to enter the diff. You just need to figure if the vent cap is working correctly. You could theoretically remove the fill plug, apply a slight vacuum on the port using a small hand vacuum pump and see if you can draw a vacuum. The differential is NOT a perfect seal. I imagine that if the car sits long enough, the vacuum will equalize some what and there wont be as much of an in-rush of air. I know that my 02 ZO6 has a GOOD seal and I was surprised at how much air rushed in!!
You can also Drive the car and get it up to full operating temp. Then let it cool down to ambient outside temp and check for the vacuum. if it doesn't hold vacuum in that period of time, something is wrong!
No diff leaks in my 02 ZO6 at all!
You can also Drive the car and get it up to full operating temp. Then let it cool down to ambient outside temp and check for the vacuum. if it doesn't hold vacuum in that period of time, something is wrong!No diff leaks in my 02 ZO6 at all!
Instructor
Joined: Jul 2007
Posts: 202
Likes: 9
From: Coventry, Warwickshire,
Hello, this sounds very similar to the issue that I have with my 01' coupe (16,500 miles). My diff looks to have a small leak, but I can never get it to leak when I want it too ( if that make's sense ). When I removed the fill plug to check the level it gave the impression that it was slightly pressurised. I reached up to check out if the vent valve had any evidence of oil around it-but it was perfectly dry. However, I did 'work' the vent a couple of times, and since then it has'nt leaked. This made me think that possibly the vent was not working correctly, causing the diff to get some pressure build up which in turn is causing the oil to leak (very slightly) out of the drivers side housing plate (which I'm lead to believe is generally not a great seal to begin with). I'm not totally convinced, but if you add to this that it only happens when the weather is really hot (by our standards-not very often) this would cause the oil to be possibly thinner than normal.Keep us informed if you find anything out, as I will should I get any more information. 
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