Front Diff, Transfer Case, and Auto Transmission Breathers

All the metal caps on my truck were 1ways. I took them off and confirmed. Couldn't blow out of them. Front diff, rear, transfer

 

That is very interesting. You would think they would vent air out but not in.

 

Yes I believe that is what they should be, maybe just a description issue? They probably designed it that way to keep things clean vs atmospheric breathers especially with the long fluid change intervals. Shouldn't have the issue that the rear diff has since they aren't as low. Some people have had moisture issues with the ADD but I bet a lot of them are from broken or disconnected breather lines or poor sealing.

 

The dorman replacements metal caps are true in and out .

 

Its designed to be used in the event of a water crossing. Most rivers are significantly colder than ambient temp causing a rapid cooling of the casing results in an intake of air due to the temp change. I believe it should breath in and out as its name suggests but toyota might have wanted it to keep pressure for fluid longevity, either way I think it contributed to my leak.

 

I just hunted down my silver T case breather ends, removed them and tested them. when I removed the breather on the T case (not actuator) i got positive pressure, air releasing on the hose coming from the T case. sounded like an almost empty bike tube deflating for about 5 seconds. there was some positive pressure in there that the breather was not letting out is that normal? truck has not been used for a few days. Upon testing my breather, it is designed to air escape from the T case but will not let any air into the t case and it does seem to be testing fine which is odd since I had positive pressure. It is spring loaded however so perhaps the spring got weak and the blocking device sags down and will not let the pressure release out of the t case when its faced upright the way its mounted. not sure if its designed to have some amount of pressure in the T case and at a certain amount it releases/vents? anyway, I'm going to look for a replacement breather now. any tips on a true two way thats not as expensive as the arb unit?

 

i got the 30 dollar alternative to the ARB unit on Amazon and it works great. Bought 2 of them

 

this unit?

$46 Differential Axle Breather Replacement for ARB 170112 Kit Compatible with Drivetrain Assemblies, Differentials, Transmission and Transfer Case of 4×4 4WD Accessories

https://www.amazon.com/dp/B07V3C77HY

 

very similar except mine didnt have any text on the filter head.

 

Vacuum pressure does seem more likely although the one way breathers will require a certain amount of pressure to open so will hold some amount of pressure. It is possible that they intend for it to hold a bit and use a stiffer spring to achieve that as well. It would actually help prevent a vacuum forming when things cool.