4wd Extended Diff Breathers
Diff Breather extensions are an essential modification if you plan on doing any kind of water crossing when touring in the outback. Even if you don't plan on going through much water, diff breather extensions allow you to keep the beathers in a high area out of the way of dust, and other grit that may cause your outback adventure to grind to a halt!
Extended diff breathers have a filter element which keeps the air clean and eliminates dust that will destroy your diff gears. A very small investment in some breathers will save you a lot of hard work later on. The best thing is, you can install them yourself!
Beather extensions can also be used on the gearbox and transfer case. The vehicle has standard diff breathers installed which allow for expansion. As the diff heats up, a one way valve allows hot air out of the diff. If the diff is cooled quickly the air is sucked in via oil seals. This is ok for the factory vehicle until you start doing water crossings. If the diffs are underwater, they will suck in water.
Diffs Heat Up
Picture this scenario. You are driving for some time and your drivetrain has created a lot of heat through the friction on the diff gears. The air inside your diff housings, gearbox and transfer case has heated up. When the temperature of air increases, it expands. This means the volume it requires is now larger causing pressure inside the diff casings. The hot air attempts to vent through the factory diff breather.
The factory diff breather is a one way valve which allows the hot air to escape the diff. If this is to become blocked with dirt or mud, the pressure could be enough to force oil out through the next weakest seal. This is not a good situation for your diff.
Diffs Cool Down
Continuing the scenario. Now your drivetrain is nice and warm and you've approached a creek crossing deep enough that it's going to come up past your door sills. You're easily going to submerge or douse the drivetrain. As you forge through the water, the drivetrain is suddenly cooled causing the air inside to reduce in volume. The air from outside wants to enter the diff to equalise the pressure. Often it will enter via the oil seals in your diff.
If the hubs are underwater, it won't be air that enters the diff. Factory breathers are useless if fully submerged in water. You will end up with an oily water sludge in your diff housing which will not lubricate the gears.
Extending Your Diff Breathers
Aftermarket diff breather kits are available and are very good quality. The kit works by attaching breather hose to the diff (often replacing the factory breather) and routing them up to the firewall or an area where it won't get flooded by water.
The hoses are run under the body of the vehicle and to the front of the car where a filter block is mounted in the enginebay as high as possible. Breather filters prevent dust and moisture entering the diff breather lines.
Make sure to leave enough hose to allow the diffs to move up and down with the suspension as your car flexes over rocks and other terrain.