Fresh refill of tranny and transfer case oil: Where did it go?

[melvinjo]

Just did a rebuild on my 3 speed tranny. I refilled both the tranny and transfer case by using the fill hole technique. In other words, slowly fill up both units until the oil starts to dribble out of the corresponding fill hole

Si I drove it about 10 miles and checked for leaks: I have small one coming out of the parking brake drum area

Out of habit, I checked the transfer case oil level. And it appears it is almost empty? I cant feel the oil level at the fill hole with my pinky, and it barley comes out of the drain plug hole

I would say between the tranny and transfer case i put in almost 1 full gallon. Tranny is not overfilled

Am I over imagining things? There is no way I lost a large amount of transfer case oil on a 10 mile trip. There is barely any oil anywhere on the transfer case except around the parking brake drum

 

[SteveH]

Well, the parking brake drum area (a famous FJ40 leak point) is fed by the transfer case. I'd simply refill the xfer case and take another test drive and recheck. You (obviously) never want to drive with the transfer case underfilled. Who knows why it turned up mostly empty.

Long term, whatever else you do, be sure you remove the factory vent cap on the xfer case, and install and run a 3/8 piece of fuel line up to a high location. This will keep the transfer case from pressurizing, will reduce parking brake drum leaks, and help prevent the transmission from filling with the oil that is supposed to be in the transfer case.

You never want pressure or vacuum in an oil filled cavity on a vehicle. Axle vents should be handled the same way. The transmission does not need venting, as it vents through the shift tower.

 

[melvinjo]

I have heard about the pressure thing, but I dont have that issue here. The vent cap was just cleaned along with the recent tranny rebuild. Also, the transmission is not over filled, a common sign of a blocked vent cap. I beleive I will replace it with a fuel line as mentioned just as a
precaution

 

[BeerM3]

Long term, whatever else you do, be sure you remove the factory vent cap on the xfer case, and install and run a 3/8 piece of fuel line up to a high location. This will keep the transfer case from pressurizing, will reduce parking brake drum leaks, and help prevent the transmission from filling with the oil that is supposed to be in the transfer case.

I ask this without an understanding of how the internals of the stock vents work, but wouldn't an open line allow humid air into the transfer case or axle? On the TC & transmission, would the shared transfer line between the fill plugs that some folks sell be a more weather-tight option?

 

[S4Cruiser]

I have filled the tcase and then checked after driving and noticed the same difference as you. In my case it was based off the level of the truck being different for when filling and checking. Filled the tcase when the truck was on the lift and then checked with on the ground. Lifted truck to add some and it started dribbling out the fill hole.

 

[SteveH]

I ask this without an understanding of how the internals of the stock vents work, but wouldn't an open line allow humid air into the transfer case or axle? On the TC & transmission, would the shared transfer line between the fill plugs that some folks sell be a more weather-tight option?

Interesting thought. I live in Colorado where humidity is a non-issue. Also, normal vehicle operation heats up the oil and (in theory) drives off any moisture over time. Vehicles (like old farm tractors) that are parked for years outdoors often end up with water in the bottom of the oil pan or transmission case, due repeated condensation forming inside the cavities. I have never seen any water issues with gear oil in a Land Cruiser that weren't cause by immersion, so I guess I wouldn't sweat that. In theory, you are correct, but IMO the 'tube between the fill plugs' is a bit of a stop-gap measure versus replacing the seal between the cavities, and then venting the xfer case.

 

[BeerM3]

In theory, you are correct, but IMO the 'tube between the fill plugs' is a bit of a stop-gap measure versus replacing the seal between the cavities, and then venting the xfer case.

Good points. That's pretty much the way I've looked at it too (running a line between them). It's not a bad option, but it's not as good as a proper fix if you're tearing into it.

 

[ginmtb]

Check this thread:

Transmission to Transfer Case Bypass Hose