harryjames

Hi. I just bought a 2002 Mustang convertible with an automatic and V-6. The last Mustang that I owned was a 1991, and it had an axel vent with a cap that twisted and could pop up and down. That is, the cap sat loose on the vent tube that it covered. The vent tube was on top of the rear axel on the passanger's side of the car. The cap was prone to rusting shut, and with every oil change, I used to crawl under the back of the car and work the cap free, and spraying WD-40 on it as well.

My 2002 Mustang has a tube about one inch tall coming out of the top of the rear axel as well. But there doesn't seem to be a free floating cap on it. I have to crawl under the car when its up on blocks, so its hard to get a good look at this tube. I don't want to just start twisting it with a wrench.

Is anyone familiar with this item? The top of the tube feels like it is somewhat porous, rather than being smooth flat metal. Judging from the fact that I can find almost no discussion of the need to routinely free up vents that are rusted shut leads me to believe that the vent has changed from the 1991 model, and it breathes by itself without the need of a loose movable cap.

Any I right? Does the 2002 Mustang have an axel vent that is designed without a cap, and thus has no cap that can rust shut, and therefore no routine inspection is necessary?

mustang51js

i just had my rear worked on because it was squeaking and the guy showed me that my vent cap was smashed down, he took it off and said i dont need it, so i guess thats your answer.

67mustang302

The primary reason for the vent cap is pressure control of the axle housing. As the diff heats up the oil gets hot and produces some vapor, without venting it the pressure can build up and squeeze past the seals and cause leaks. Also when you suddenly go through a large puddle of water the housing rapidly cools causing the gasses inside to contract and try to draw a slight vacuum. Without the vent it would suck air in through the weakest parts, mainly the axle and pinion seals. If they're under water in the puddle they suck water in as well and you emulsify the oil in the housing. Ideally you want a tube running up away from the vent so it's high enough that it stays above whatever water puddles you may go through, so it just moves air back and forth.

mattdel

harryjames

Thanks for the replies. I crawled under the car again this afternoon with a mirror and a trouble light. My vent tube had a cap on it that was rusted tightly shut. The under coating seemed to cover the tube as well. I doused it with WD-40 and took a wrench to it and its spinning and poping freely now, like the one on my 1991 car.

I would bet that most of the older Mustangs out there have vent caps rusted shut. I don't know why people apparently are not blowing out there axel seals right and left. Maybe a frozen cap still leaks vapors when it has to. On my 1991 I had axel fluid blow out the seals and they soaked the rear brake linings with fluid, causing an expensive repair job. So I cared a lot about this matter.

Mustang51js, I don't know what the top of the vent tube looks like without the cap. Hopefully the air passages are still small enough to keep dirt out. When you next get your car on a lift, you could look with a mirror, or feel what the top of the tube is like with your fingers. You don't want no big open hole there I am sure. A new vent should be cheap and easy to put on if you need one. But without the cap, you know your vent is open anyway.

67Mustang302, thanks for the explanation of why the vent is needed. If I see deep water over the road, I'm just not crossing it. I'll get out and stop traffic and make a U-turn, or back up if I have to. I'm not required to ruin my car. I'll tell that to any cop.