[FJtest]

Has anyone else had issues with unmodified rear axle vent not working? I went to change out the fluid yesterday and the fill plug hissed like crazy when I cracked it. Kinda freaked me out looking for the snake that snuck up on me!

Tip: Remove the fill plug before draining. The fluid will drain faster and... if it is stuck, you are not left without transportation until you get it fixed.

Time to whip out the extra long pipe cleaners I guess.

NO pipe cleaner needed - that is the way it is supposed to work.

That exact same thing happened to me the first time I changed the rear diff lube on my '14. However, the hissing wasn't from air pressure escaping from inside the axle, it was air being drawn IN (vacuum within the axle housing).

If you take the vent fitting apart, you will find that it's NOT just a vent fitting, it's a check valve. Air will be released from the valve when the rear axle heats up and the air inside expands ... when the axle cools, the air will contract, but the check valve will not let air back in to equalize the pressure - resulting in a partial vacuum (lower than ambient pressure). I don't know why Toyota chose this setup (reduce the chance of axle seal leakage??), but it's the same on the breather for the front diff. The transfer case just has a straight-through breather fitting.

I added extended an breather (without check valve) to the rear axle (routed up into the jack compartment) and haven't had any issues with axle seal leakage or sulphurous gear oil fumes in the passenger compartment.

 

[FJtest]

Thanks! You saved me from diving under my truck for a few hours.


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But adding an extension fitting and tubing to bring both the diff lock and differential breathers up higher is still a good modification if you ever think you might find yourself in axle deep water. The breathers don't have any kind of filtration, and it wouldn't be impossible for dust or mud to foul the check valve and let water in.

I ran separate breather hoses from the diff lock housing and rear axle housing up into the jack compartment. I was originally just going to connect both lines together with a "T" fitting and run one line up, but then I thought there might be some chance of oil mist from the diff getting into the diff lock housing, and ran separate lines. Six years later, there has been no evidence of any oil mist coming out of the end of the diff breather hose, but I still feel better with independent vent lines.