View Full Version : Rear Axle Vent

04-02-2013, 11:24 AM
I did not see any threads named "Rear Axle Vent" in a quick search, so here goes. This is a problem with another late 80s Ford. After battling with a rear seal leak for most of the time I have had the vehicle, I have come to the conclusion the axle vent must be blocked. The vent is a little mushroom type cap, twice the size at least, and appearing as one of those tire valve caps. It has a sideways wiggle to it when I toy with it. I am curious whether there is a way to check this mechanism without (oops) breaking it off or something to that effect. If it wiggles, I am presuming it is NOT a twist off cap. It does not leak. When I open the diff check screw/plug there is a pressure of air (whether pos or neg I am not sure) situation, leading me to suspect this is what causes the leak. ????


04-02-2013, 12:08 PM
Did a quick search on the Corral and came up with this thread:


Either way it sounds like a quick fix so hopefully the carb cleaner route will work for you.


04-02-2013, 03:09 PM
Good idea

I used an fittings ran a peice of hose and I mini k&n breather

04-02-2013, 03:15 PM
Thanks so much for the prompt input. Now the question is ---how do you open/remove the vent---turn the cap?? I have never looked at it closely other than to know it's fairly flimsy to play with---jiggly. I did not see any base on it, but never really looked. I'm sure it is plugged. Too bad I did not realize it long ago.

John R

04-02-2013, 08:47 PM
OK Tom, I see what you mean. I started this job hours back because I have no clue how much fluid may have sneaked out on me at the diff case--I couldn't imagine much---and had to get this job started today. Incidentally, this situation results from a leak at the diff case and it must be my fault in not securing it well after the bearing seal job--not sure on that. The diff was fine for weeks after. I wasn't going to drive the car again until this leak is fixed. As far as the vent is concerned, I used a deep socket and took the whole unit off and allowed me to figure out how it works. The cap floats on a relaxed spring. When up, it allows air to escape. When down, it is closed ??--and this presumes that submersion in water closes the valve cap by compression or such? The spring doesn't have much tension and I see how the cap could get stuck open or closed. I couldn't tell whether this one was bad except it was sluggish. I soaked it in carb cleaner and blew it out with air----it appears acceptable so I reinstalled it. It was not difficult to remove (surprised!), but the big deal is to avoid getting crud down the hole. 10 years ago a shop opened the diff case and reinstalled the cover without a gasket. I should have bought a gasket when I did the work because I did not used the gobs of silicone they used in securing it. I literally had to pry the edge of the cover with a flat bladed putty knife and hammer to get it off.

04-03-2013, 06:42 AM
You should know that almost everything that has come with a rear diff in the last 10 years has had the cover sealed with oil resistant RTV. Not everyone seems to be able to restrain themselves from globbing on as much as they can fit, though. As an example, the workshop manual for an 05 Mustang calls for a 2mm bead around the cover. This is done by a machine at assembly, but takes a steady hand and a caulk gun in the field. On the flipside, Accurate Engines, a local reman outfit near me, puts high temp, low tensile RTV on absolutely everything and it's disgusting. They use the orange junk that expands on contact with oil and then dissolves in it. We get so much of their crap that they deny warranty on, and we find it everyplace: O-rings, rubber front cover seals, 5.4L intakes, everywhere, and as much as it takes to make it out the door not leaking.

04-03-2013, 10:53 AM
I've never used a gasket on the 8.8's in my cars. Always a very thin layer of RTV, let it sit for about ten minutes, and bolt up the cover. The difference is I have T/A covers on both my cars so they torque down way better than the tin stamped units from the factory.

All I can say is thank you for a great thread! I am going to check the breather on my Mustang as I have not cleaned that damn thing in a couple of years.


04-03-2013, 11:38 PM
Thanks for the comments guys. The Ford diff cover is hard plastic and you really have to scrub it with a flat scraper to release some of the adhesive. I also used a single edge blade---and then you have to work along the raised edge to get it all off. On Thursday (tomorrow), I will clean it up with brake cleaner and so clean the case edge and put all together. Today I bought the gasket and another tube of black gasket maker (the tube I used last month was old stuff). I am all confused now as to using any adhesive, but will likely use a light surface of it on the gasket. Tom, I feel like you would have to twist my arm to make me install it dry!!! Dunno why?

All of the jobs I have done involving gaskets--water pumps/thermostats, etc, --have not had a sealant problem, so I was surprised this one failed (and I had done the diff 15 years ago with no issues). ...So the reasoning that maybe excessive internal case pressure was pushing the oil out at a weak spot.

As far as making the job tight, the secret to me has always been to make sure the surfaces are CLEAN! As far as this job is concerned, I just hope I solved the seal leak problem on the RR wheel. Another thought --the book calls for 3.8 pints of oil in the case. This amount does not bring the level to the filler hole (contrary to my 1970s education that the level should be at the hole), so I wonder if there is such a thing as overfilling the diff and causing a seal leak at the wheel end. Whew....too much on this subject I know!

04-04-2013, 09:45 PM
OK--the job was finished earlier this afternoon. I tacked the gasket to the cover, and (Tom don't read this part), I put an itsy-bitsy bead of gasket maker along the raised lip on the cover which fits into the case. We'll see how this goes, but I'm leaving the Towncar in the garage for the weekend. For Friday, I'm taking the '88 Thunderbird to work. It has a coolant leak which has been spooky. Sometimes it leaks and sometimes it doesn't--I think its the timing cover. I also applied for Social Security this week, so I wonder how much longer I can screw-up DIY jobs!! My 93 year old aunt just suffered a major stroke yesterday (found out today) and I hope to be as healthy as she was at 90
....if I could even live that long.