Transfer Case Pressurized

Hello all,

This is my 1st post here, and I am in need of some advise. Was doing some routine maintenance on my 2019 TRD-OR (A/T, 58K miles). I have had zero problems with the truck since I bought it new, I stick to the maintenance schedule for everything, etc. I was checking the rear diff, front diff, and transfer case to make sure the oil/fluid was at the correct level for peace of mind. I want to note the truck was sitting in the garage for almost 48hrs before checking these fluids. Checked the rear and front diffs, everything was good to go.

Went to check the transfer case, started to unscrew the fill plug. I noticed it was pretty pressurized (I unscrewed the plug slowly to begin with, no fluid came out with the pressurized air). Thought it was odd and checked the level, perfectly fine.

This being my 1st truck I am slowly learning a lot of "truck things" on my own. I dug around on here and found a post about the TC breathers and its hoses. Crawled under there tonight and popped the one that is easiest to get to (It is the one on the black actuator). Blew into it a little, seemed like no blockage. Didn't have enough time to pull the one off the top and blow some air into it to see if its clogged. Double checked for any "seepage" or any type of leaks around the TC, nothing at all.

So my question/concern is; is some type of pressure normal, even after sitting for almost 48hrs in the TC? I called 4 stealerships and got 4 different answers... I am hoping I am over thinking this and its nothing to worry about. Any help would be appreciated!

 

Do you know for sure that it was positive pressure? Could it have been a vacuum?

 

Now that I think about it, not 100%. Sounded like it was blowing out, but I don't remember feeling it on my hand. If was was sucking in/vacuum, is that normal? The diffs had zero pressure when I opened the fill plug on them. It was more of a hissing sound then a sucking sound.

 

Normal.

 

Still don't understand why there was pressure (especially after sitting that long) if it has breathers on it.

 

Someone correct me if I am wrong, but I think the factory breathers allow air out, but not air in. Since they are not filtered, letting air in would allow for dust and dirt to get in there.
So as the diff heats up the fluid expands and pushes air out of the breather (without the breather it would blow oil out the seals) Then as it cools down it just creates a vacuum in there.

 

They suck instead of blow.

 

Ball valves have very good seals. If it is not going to let fine particles and water in, it is going to seal air pretty well. Also, it likely has a fine coating of oil vapor on it from breathing, which helps the sealing action.


When I extended the breather on the rear diff, I was similarly surprised when the stock breather was vacuumed to the hole and sucked in air.

 

The diffs were fine, it was the TC with the pressure. When I took the hose off the TC actuator I could only blow air out/into the hose. Wouldn't let me suck air in. I guess its doing its job. That is why I was surprised with it having pressure in it.

 

Like mega-maid.

 

I believe that the TC is connected to the front diff and the MT, when applicable.

 

If it had cooled down, yes, there might be a slight vacuum. This is why, after every deep water crossing or extended time in water above the axles/X-fer case, you are supposed to hopefully] change the fluids because as they rapidly cool down, they can pull water past the seals and contaminate the fluid.

 

The two breathers up in the engine bay (front diff and transfer case) I believe are two-way unlike the rear diff. I have not verified myself on those but based on all the other posts on breather extension / locations. Surprising that the TC would be pressurized.

 

No water adventures since it is my daily. Could cold weather create the vacuum? Garage is between 35 & 50. I just want to make sure I'm not going to mess up seals or break something.

 

Here is what the insides of the rear diff breather looks like. I did not remove/replace my front or T case breathers, but I imagine they are the same type.

 

Pretty much nothing to it. They look the same for the TC, just got done crawling from under the truck and followed the lines (I think I stayed with them the whole time tracing them). The one from the TC actuator, and one from the top of the TC run up on top of the transmission. You can kind of see them from the back of the engine bay and they both look like that. I got both hoses off and blew into them, neither seemed like they were blocked. So I am at a lost on why there was pressure in the TC when I checked the fluid.

 

I would not excessively worry about it to be honest. I could see where it would get some pressure from heat generated in use. I cannot remember noticing any pressure when changing mine, but would not be surprised if it did.

The rear diff mod relocation came about from people towing boats and stuff and then backing into a boat ramp where the diff is hot and cooled quickly where they are worried about sucking in water. so they extend the breather into the tail light or fuel filler area to raise it up out of the water. Pressure differential and all causing a vacuum and the worry that quick cooling would suck in water. But I do not think in normal use it is something to be worried about.

 

Guessing since there isn't much concern about the issue, wont worry too much about it and will just keep an eye on it. Thank you everyone for the input/feedback, appreciate it very much.