What do diff breathers do? Differential and Transmission Breather Kits

What do diff breathers do? Differential and Transmission Breather Kits

Why do you need diff breathers? The need for extended breather lines

When offroading in New Zealand, it's pretty much guaranteed that you will frequently encounter water. In fact length wise rivers span over 180,000km throughout New Zealand! But aside from rivers being almost unavoidable, they are a ton of fun to cross – so modifying a vehicle for water crossings is top of the to do list for many.  


Factory installed breathers are generally located on top of the axle housing, gearbox and transfer case in exposed positions. This is exactly where you don't want them on an offroad vehicle. In exposed low down positions they are easily submerged, damaged and blocked by mud and debris.  

Crossing water without the appropriate modifications can create some very costly problems or leave you stranded when water gets where it shouldn’t be! Luckily the solution to this issue is very simple and it doesn’t cost a lot of money. 

What do diff breathers do?

Well in short, they allow the equalization of air pressures. 

During operation the drive train of your vehicle heats up, this heat expands the air inside your gearbox and differentials creating a positive pressure. When these hot components meet cold water they are rapidly cooled and this creates a strong vacuum effect. This pressure equalization process happens quickly, and if breathers are submerged while this takes place then they act like a straw and will suck water inside.  

Why not just remove the breather, blank the hole off and be done with it? Well, if there was no breathers (Or blocked breathers) then outside debris would be sucked in through the next weakest link, usually the axle seals or pinion seals. This is why a clean free flowing breather is so important in a vehicle used off-road.   

The above image is water contaminated oil removed from the rear differential of a Toyota Hilux. Having lost its clean golden colour and turned a milky white, this is referred to as emulsified water. Its been churned up and thoroughly mixed by the differential while driving. A very small amount of water can do this, and it will significantly reduce the life of bearings and other mechanical components. Check out the following link for more info on The effects of water in oil 

Simple Installation

Breather kits are perfect for DIY installation, most vehicles require limited mechanical knowledge and can be installed with basic hand tools.  

From finding and removing factory breathers, attaching, and routing extended breather lines and mounting the breather housing to the firewall - we have you covered with informative, simple instructions for adding diff and transmission breathers 

Extending factory diff breathers is a sensible modification if you’re planning any water crossings in your 4wd. You can check out our range of diff breather kits at this link All Breather Kits They work great and its almost guaranteed these kits will help you in service costs and repairs in the long run, so they are a worth while investment.

Where to mount the Breather housing

Usually the best place to mount the breather housing is in a high position against the firewall. This is well above normal water crossing heights. For those deeper crossings, having the breather housing mounted high in the engine bay allows it to complete the pressure equalization process before being submerged by water. The filters Flatout Offroad uses, are not restrictive and allow the free movement of air. An added bonus is once the pressure equalization process is complete, these filters will not allow water ingress through them, even when submerged! 

Maintaining your breather extension / relocation kit

The breather housing shields the filters from a majority of dirt and dust so they are extremely low maintenance, and rarely require any input to keep functioning correctly. However checking the state of your breathers periodically is still recommended. On occasion hoses can be snagged by branches and filters can become partially clogged with dust. Check fittings for a secure fit, and that hose is located correctly. Inspection of these areas will keep the kit functioning as intended.

Planning the Perfect 4wd Trip

Ensure you are capable of the upcoming adventure and account for everything when planning your 4wd trip from navigation to track choice and accessories.

Discover your Favorite Trails

Throughout New Zealand, we are lucky enough to have a wide range of off-roading opportunities, for any skill level. With our beautiful beaches and rugged terrain, we believe New Zealand is one of the world’s leading off-road destinations.  

 From Ninety Mile Beach, the Forgotten World Highway, and the 42 Traverse in the North Island, to Skippers Canyon and Clarence Valley in the South Island, the opportunities for exciting trails and outstanding views are endless.


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