Diff Breather

A proper bidirectional seal should not depend on DP to seal. The diff breather is nothing but a relief valve. The axel seals should keep the inside in and the outside out without assistance. If the differential can heat up enough to overcome the seal, then the answer would be to vent it hence the relief valve. But a relief valve that creates a DP that overcomes the seals keeping the external pressure out is kind of stupid. As is a poorly constructed check/relief valve for the environment. I don't normally question the designer's intentions, not true because I have designers working for me, not in the automotive industry, but in this case... using a check valve to regulate internal pressure in a vulnerable area that can allow internal contamination doesn't make sense. Thus the diff breather mod.

 

I changed my diff fluids today and the rear diff hissed quite a bit when I removed the fill plug. Guess I need to order some breathers.

 

I have not heard anyone mention oil viscosity and heat affects in your discussion re the expanding and contracting diff oil What if the oil thins when heated, the rotating gears cavitate the oil which causes air to be introduced into the oil thus creating an expansion and contraction during heating and then cooling?

 

Do the diff breather mod and be done with it...

 

I did some more Googling last night and found posts by Land Cruisers, 4Runners, Tacoma's and others that also held discussions about the one way vent, pressure, temperature, thermodynamics, but sadly, no discussion of enchiladas. I also found a post in an industrial group discussion on shaft seals (Kalsi Engineering rotary shaft seal) consideration that mentioned maintaining a slight overpressure on the lubricated side of the shaft allows some beveled seals to "rotate along the shaft axis, thereby reducing the seal shaft interface for lower friction and longer seal life". Whether our seals are of such design is unknown and not worth my time to research.

Otherwise, the off roading, mudder, yee-haw, boat trailering crowd all echoed the same concern/problem, hot axle housing suddenly immersed in cool water, mud, baby oil, or other liquid was a recipe to contaminate the gear oil due to the thermodynamic effects already discussed. If you mudd, boat, drive into your neighbors pool, do the breather mod. If not, you're probably fine replacing the oem vent every 10 years to avoid a corrosion induced vent lock.

Good discussion.

 

So my food container seals work as designed! Yay!!!

 

Do you keep enchiladas in them?

 

Last meal I had out of that container was a combination of an Easter Ham slice, leftover restaurant linguine with Francese sauce topped with Mama Hand Models homemade green bean simmered in pork fat.

Heated in a microwave for 2 minutes and eaten with a gas station plastic fork.

 

I’m almost certain it only lets air out not air in.

 

Yum!

 

Sounds like the best option is to design a hose extension with a dual pressure/vacuum vent design.

Leave the stock overpressure valve on the extension, then T off the same breather line with a vacuum vent. It would be similar to having both the stock valve on AND a similar stock valve but flipped around backwards. You would want to design the backwards vacuum vent so that it only lets air in at or right below atmospheric pressure though.

My guess is you would want internal pressure anywhere between 14.7 psi to whatever the current stock valve set point is. But then at altitude pressure is a little lower (where I live it’s 12.4 psi) so it would vary. This could all be a moot point though, because you would actually want to design the new inbreathing set point to a % psi above the failure point of the seals (assuming that even is your first point of water ingress and not the pumpkin seal).

But then again we’re overthinking it, just swap your gear oil a couple days after deep water crossings!