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Diff Breathers; why you should fit them to your 4WD

What are diff breathers?

An extended diff breather is a piece of hose that runs from your differential to a higher point on the vehicle (usually the engine bay). The hose is connected to the diff via a push fitting or hosetail and should have a filter on the other end. They are one of the first modifications you should do to a 4WD that is used off road.

Diff breathers in the engine bay

Diff breathers in the engine bay

Why are Diff Breathers important?

Extended diff breathers are extremely important insurance for your 4WD if you drive through water. In essence, when you go through a puddle that is near or above diff height, you are dunking a hot differential into cold water.

When you dunk something hot into cold water, it shrinks, and in the case of a diff, tries to suck air in. If you don’t have extended differential breathers, the line of least resistance is usually through your oil seals or the factory breather. This is problem when your diffs are underwater, as the water passes through the seals and mixes in with your oil inside the differential.

Prado muddy water over the diffs

To protect your differentials

Extended diff breathers also allow for hot air to exit through the hose. By fitting diff breathers, when your diff gets dunked in water it will contract, and suck air in through the breather (as a pose to water through the seals!).

Differentials are designed to run oil to keep the bearings and gears lubricated. When you add water into the mix you will damage both the gears and bearings, and it leads to expensive repairs. Trust me (I’ve had this issue with my Hilux as I never fitted breathers before taking it through puddles!)

Do I need diff breathers?

Diff Breathers are cheap insurance. To buy a kit and fit it might cost you $40 – $80 (plus labour if you can’t fit it yourself). To replace or rebuild a differential you would be looking at $600 – $2000. In my opinion, even if you are only going through water every now and again it is well worth it. Water in the differential will eventually make them whine and they will wear out much quicker.

Differential breathers

Water crossings will make your diffs suck water in

Factory breathers are rarely adequate

Most vehicles will come with a factory valve or breather, but very rarely are they up high enough and they have a habit of blocking and causing other issues. If you want your differentials to live a long, healthy life, fit breathers, change the oil regularly and let things cool down a bit before ploughing through water.

Your breathers should go to a point that is higher than where water will get to in a worst case scenario.

Fitting diff breathers

Fitting diff breathers is a piece of cake. Even those with minimal mechanical skill shouldn’t have an issue. To do it, you simply remove the breather that is in the diff (usually on the top of the pumkin) with a spanner.

Put thread tape on the new fitting (most already come with it on), and screw it in. Run the hose from the fitting to the engine bay (carefully avoiding any hot components) and cable tie it along the way. Once in the engine bay, you simply mount a small bracket, attach the fittings and a filter and you are done! Make sure that you leave enough hose to allow the vehicle to flex properly. If you don’t, you will pull the hoses out the moment your differential moves with the suspension!

Water crossings in the Kimberley

If you are doing crossings like this without breathers expect to wreck your diffs quickly

Buying a Diff Breather Kit

I looked at buying the individual components to make a kit up, and then decided it wasn’t worth it. To buy the parts yourself you will hardly save more than a few dollars, and you have to drive around to pick everything up.

My suggestion is to jump on eBay and grab a kit. As long as you know what size fitting your differential takes it’s a piece of cake. You can get two breathers (for both diffs) with the fittings, hose and filters for about $45 – $80. If you want 4 breathers (for the diffs, gearbox and transfer case) you will be paying around $80 – $110. Order it, wait a few days and it will arrive on your door step!

Making your own kits up

Most quality hose shops will have everything you need, so if you do want to purchase the parts individually just head to your local pneumatics shop. Make sure you get oil resistant hose, thread tape (as required), filters and a bracket (aluminium angle works brilliantly).

Gearbox and Transfer case breathers

While doing the differentials, it’s worth looking at your gearbox and transfer case. These will both have breathers as well, and you can run hose right up into the engine bay too. Some of these aren’t as easy to do though (like our Isuzu Dmax) so you might want to look into it before purchasing the extra hose and fittings.

Let your vehicle cool down before going through water!

One of the most important steps to take before crossing water is to let your vehicle cool down for 10 minutes. Whilst this might not always be practical, it is much better than dunking hot components straight into water! You should be stopping to check the crossing out anyway; its part of 15 ways to avoid drowning your 4WD!

Water crossings are a part of four wheel driving

Crossing a river

I wish I had fitted diff breathers to my Hilux earlier, and recommend them to everyone who might go through water. They can save you a lot of money in the long run!

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4 comments… add one
  • Bill August 4, 2020, 8:23 AM

    You lost me at the first sentence; “A diff breather is a piece of of hose . . .” What?
    I did persist though. Then I found this; “If you don’t have differential breathers, the line of least resistance is usually through . . . . the factory breather”.
    That’s when I stopped to write this and moved on.
    If you are going to write something of a technical nature and maintain a semblance of credibility, you had better get your use of language correct beforehand.

  • Aaron Schubert August 4, 2020, 5:50 PM

    Hi Bill,

    Thanks for your valued comment on my 8 year old article. I’ve made some amendments, which I hope you’ll find acceptable

    Have a great day
    Aaron

  • John Mincevich August 28, 2020, 7:49 AM

    replaced 2000 grand cherokee transfercase. Cant figure out if breather line get attached to vacumn or just run end up high to nothing

  • Aaron Schubert August 28, 2020, 4:36 PM

    Hi John,

    How was it prior? I would imagine the breather would run into the engine bay, and have a small filter on the end, but could be wrong

    All the best
    Aaron

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