Rear Diff Breather Extension Install

[Bad1975]

Problem is the one way (check) valve. When your hot diff is submerged in cold water, the air inside it quickly cools causing a drop in air pressure. This sucks in water around the axle seals since the check valve closes.
Edit:
Here is article about it

Why You Need Diff Breathers

photo by Luka Banda via iStock A huge wave comes raging over your windscreen, your engine screaming, and your seat getting dirtier and dirtier – congrats, yo

www.4wdtalk.com

The math states otherwise, the 1/4 steel axle housing will transfer the temperature change very rapidly, however both the oil and air inside the axle are excellent insulators and will cause the reaction a significant delay to cool those two volumes down(anywhere from 3-10 minutes). The math also states the pressure differential it could develop if instantaneous temperature transfer could occur from 250F to 33F at 5000' is <4 PSI and ~4 PSI at sea level. The higher the elevation the less differential it can develop. Since it's not going to rapidly cool the oil and air it doesn't pose the risk they want you to believe. Been there done that and nothing ever got into my axles, with the breather on the axle.

The bigger worry would be the axle shaft contracting due to the rapid temperature change, but rubber expands as its temperature decreases.

These simple breathers have been around forever and worked just fine; they do however require periodic maintenance.

The front is the one to be concerned with since water can lift the cap up when entering water too quickly, but even then it would likely be less than a few grams of water it would allow in before the water forced it to seal anyway.

If we are going to freak out about breathers lets mention the other style is open to the air allowing dirt into your diff at all times. To each there own but neither style is a concern to me.

 

[ultane]

When I lived in the Charleston SC area, frequent street flooding was common. More that one friend of mine who drove Tahoe’s would have their differential fill with the salt water in the streets. They soon learned that if that happened, to get to a competent shop to have them drained, cleaned out, and refilled.

 

[MSINAL]

The math states otherwise, the 1/4 steel axle housing will transfer the temperature change very rapidly, however both the oil and air inside the axle are excellent insulators and will cause the reaction a significant delay to cool those two volumes down(anywhere from 3-10 minutes). The math also states the pressure differential it could develop if instantaneous temperature transfer could occur from 250F to 33F at 5000' is <4 PSI and ~4 PSI at sea level. The higher the elevation the less differential it can develop. Since it's not going to rapidly cool the oil and air it doesn't pose the risk they want you to believe. Been there done that and nothing ever got into my axles, with the breather on the axle.

The bigger worry would be the axle shaft contracting due to the rapid temperature change, but rubber expands as its temperature decreases.

These simple breathers have been around forever and worked just fine; they do however require periodic maintenance.

The front is the one to be concerned with since water can lift the cap up when entering water too quickly, but even then it would likely be less than a few grams of water it would allow in before the water forced it to seal anyway.

If we are going to freak out about breathers lets mention the other style is open to the air allowing dirt into your diff at all times. To each there own but neither style is a concern to me.

"lets mention the other style is open to the air allowing dirt into your diff at all times"

I'm not a saying that check valve breathers need to be eradicated, the people designing powertrains know far more than me about it, and they choose check valves for a reason. The open breathers however, make sense to me for people that are crossing and stopping in rivers with drivetrain submerged. Open breather in engine compartment is less likely to fail as well for those in rust inducing environments.

Edit: i scoured the internet trying to determine why check valves are used. Here is the limited info i could find, it's all mostly subjective from 4x4 sites:

- Check valves dont seal completely, so they limit water ingress but not air. Not sure i believe this.

• Long hose runs can be a potential for condensation to drain into diff. Plausible and concerning.
• Older toyota vehicles used a bellow (accumulator) to create a sealed system allowing for expansion and contraction of air. Seems like the perfect solution!
• People have put balloons on the diff vent to mimic the bellow system. I wont be recommending this to anyone.
• fuel filters (one for each circuit) are used to recreate the arb breather but with better filtration. Looks sleazy.
• Expansion of air in diff is a significant safety concern as it can push oil out of axle seals and contaminate brakes. Could blow out a seal as well, potentially.
• Vacuum in diff is a much lesser concern for manufacturers, can pull seeping oil and environment at seals back into the diff.
• you should change, or at a minimum inspect, fluids after water crossings deep enough to reach the pinion and axle seals.

Good luck making a decision.