What is a diff breather and how does it work?

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Every 4X4 will have a factory-installed diff breather but these are often mounted too low, but just what is a diff breather and how does it work?

Every new four-wheel drive will have factory-installed diff breathers as well as transmission and transfer case breathers. The principal is the same, in that they’re all designed to help that particular item (diff, transmission, transfer case) release pressure (or breathe). But there’s more to it than that.


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What is a diff breather?

What makes diff breathers important, nay, vital, is that as the crown-wheel and pinion, wheel bearings, carrier bearings and oil heat up inside the diff, the air inside the diff heats up too. As the air heats up, it expands and needs to go somewhere. Instead of pushing the now pressurised air out of your seals (taking oil and bearing grease with it), it will vent through the breather that’s located at the top of your diff housing. The hot air is vented and your diff stays stable and operational.

Why do you need a diff breather?

While you want your diff to be able to release hot air, when it cools down it will want to do the reverse and breathe in and you don’t want that. Where this becomes a big problem is when we drive through water; be it a creek crossing, or putting the boat in at a boat ramp. This cools everything in the diff down very quickly, and if the factory breather tube, which is often only 4-6-inches long is underwater, it will suck a gutful of water into your diff, making your oil the consistency and look of a chocolate milkshake and this can wreck the mechanicals in no time (see below).


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Diff breather extensions are vital

The simple way to ensure you’re not going to suck water into your breather and thus diff is to extend the factory items well above where the breather heads are mounted from factory. Say, for an Amarok, they mount up on the chassis, but with an aftermarket diff breather kit, you can get them mounted way up on the firewall. Sure, you can still get water into them, but you’re going to have bigger problems than water in your diff if you do – you’ll most likely have drowned the rest of the four-wheel drive.

It’s a rather cheap bit of insurance and a simple DIY for those mechanically minded, with the average diff-breather kit going for around the $100 mark. Having your diff rebuilt when you destroy a crown wheel and pinion and bearings is going to cost closer to $2000. The kit we installed on the Amarok (pictured hereabouts) was from AOB (Air On Board). Cost us $68 direct from AOB, and came with a filter head, hoses, and push-pull connectors. The whole kit took us about 45 minutes to install, and this one came with a transmission and transfer breather as well. Well worth your time and the cost of a case of beer to add peace of mind to your river crossings.

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