Don't just relocate your stock diff breather. Mod it or you're not protected!!

[cloud]

The factory breather is a one way valve, but there is no need to buy the overpriced breather from ARB.

There are plenty of threads on breather valves here but I need to clarify something for you all.

I removed my breather while changing the oil in the diff and disassembled it to see what the deal was. Another member had told me that it wasn't a one way valve, but the ARB site claims different, though not vehicle specific as they just make general claims to apply to "many vehicles."

I have a 2003 V8 4x4 although I don't imagine there being any differences across this particular Toyota platform.

If you're going to buy some 5/16 ID fuel line to makes your own extended breather you can save a few bucks. I highly recommend it.

Before you reuse your factory breather: pull the cap off and remove the rubber plug. I chose to leave the spring in because reasons.

The cap can be popped off with vise grips and a Flathead screwdriver. Just be sure to recrimp it. I chose to use vise grips and a Flathead screwdriver to do this, I'm sure there is a better way but it worked and I'm about to drill a hole near my gas cap to run this hose down to the diff. (Edit: there was no need to drill, I never realized it but it's rubber around the gas cap. A couple slits cut with a utility knife worked alright) There are countless places to put your extended and modified breather. Do what you want, it's your life.

Here are some pics demonstrating what I'm talking about.

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[Rodtheviking]

I did this mod and used a crankcase vent filter housed behind the tail light inside the vehicle, works great.

 

[WhiteBoomer04]

Why drill a hole? on the 4th gen there is a rubber seal between the gas neck and the body. Just feed the hose up between the seal.

 

[cloud]

Why drill a hole? on the 4th gen there is a rubber seal between the gas neck and the body. Just feed the hose up between the seal.

It was a slight pain, took about fifteen minutes to route it. Seems like it will work just fine.

I don't recommend you feed it up, I'd recommend you feed it down.

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[cloud]

Not a bad idea, all in this cost me $20 and some time in the sun at 93 degrees (thermometer is in the shade)

I did this mod and used a crankcase vent filter housed behind the tail light inside the vehicle, works great.

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[Bluesky 07]

Forgive if I'm missing something obvious, but what protection is being missed by simply reusing the factory breather? You explain the how but not the why.

 

[cloud]

Forgive if I'm missing something obvious, but what protection is being missed by simply reusing the factory breather? You explain the how but not the why.

According to ARB, and also the laws of thermodynamics: when you use the diff, it heats up causing the gases inside to expand. When this happens the gases cause pressure on the breather, which in turn compresses the spring allowing the gases to escape.

With a hot diff submerged in water/mud; the diff can cool somewhat rapidly causing the gases to cool and reduce the volume in the diff. This will cause reduced pressure inside relative to outside a.k.a. a vacuum.

With the factory one way valve design, atmospheric air will not be able to flow into the diff and relieve the pressure difference.

According to ARB this leaves the housing seals as the only available entry for atmospheric air. But the reason you have low pressure is because your diff is submerged so instead of air coming in to the diff you get mud/water. This is not ideal because water promotes rust and the particles in mud will cause premature wear on your ring and pinion: like sandpaper being ground in to the gears.

Some may claim that water won't cool your diff enough to create a vacuum. I beg to differ. If you just spent ten minutes failing to cross an obstacle and finally pulled off the maneuver, and then you plow through a mud pit and get stuck (been there, done that) and have to wait for someone to hook up to your bumper and pull you out. You just might be in trouble.

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[Terminator03]

So, if I’m understanding correctly, you are saying that the rubber seal isn’t necessary once you relocate the breather since it won’t get submerged and need to seal. Is this correct?

 

[cloud]

So, if I’m understanding correctly, you are saying that the rubber seal isn’t necessary once you relocate the breather since it won’t get submerged and need to seal. Is this correct?

I cannot think of a reason why the rubber seal would still be necessary. By the time water would get into my breather up there I think I'll be parting the truck out.

Use your head, this seems like exactly what ARB sells, but I'm no expert.

There is at least one member here that doesn't believe there would ever be a situation in which a vacuum is created, that member also doesn't believe that this rubber piece creates a one-way valve. Maybe someone far more knowledgeable could chime in on this.

anybody have a spare axle that wants to do some science??

 

[Terminator03]

I cannot think of a reason why the rubber seal would still be necessary. By the time water would get into my breather up there I think I'll be parting the truck out.

Use your head, this seems like exactly what ARB sells, but I'm no expert.

There is at least one member here that doesn't believe there would ever be a situation in which a vacuum is created, that member also doesn't believe that this rubber piece creates a one-way valve. Maybe someone far more knowledgeable could chime in on this.

anybody have a spare axle that wants to do some science??

Hmm. The only reason I’m a bit bothered by this revelation is because I literally just ordered (2) new breathers (the front ones with the barb fittings) right before seeing your postings about this. I wanted to replace the engine bay one anyway since it was all rusty and messed up, so I figured this was a good excuse to get one to relocate the rear at the same time. Had I known this, I may have just ordered the front one, and used one of the old style sintered bronze breathers at the end of the hose in the rear. In hindsight, I probably should have done that anyway since as has been mentioned, if you submerged the height of your gas cap, you have bigger issues anyway!

 

[cloud]

Hmm. The only reason I’m a bit bothered by this revelation is because I literally just ordered (2) new breathers (the front ones with the barb fittings) right before seeing your postings about this. I wanted to replace the engine bay one anyway since it was all rusty and messed up, so I figured this was a good excuse to get one to relocate the rear at the same time. Had I known this, I may have just ordered the front one, and used one of the old style sintered bronze breathers at the end of the hose in the rear. In hindsight, I probably should have done that anyway since as has been mentioned, if you submerged the height of your gas cap, you have bigger issues anyway!

I'm sure you'll be happy with a better protected rear diff though!

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[Bluesky 07]

Though I’ve done it myself, seems to me the breather mod itself is second-guessing Toyota’s engineers as they surely know 4Rs will be submerged deeper than the factory-positioned breather. Yet they put it there anyway. So if the breather mod is necessary, the design is fundamentally flawed, and if modding the cap itself is also necessary, that’s an even deeper flaw.

Don’t get me wrong, I’m not saying the OP is wrong, more just thinking out loud in response to my innate reluctance to distrust those whose function it is to build a solid and reliable vehicle. On the other hand, Ford built exploding Pintos and the current loophole in helicopter fuel system crashworthiness that has needlessly killed and maimed countless people indicate that it does happen.

 

[cloud]

Though I’ve done it myself, seems to me the breather mod itself is second-guessing Toyota’s engineers as they surely know 4Rs will be submerged deeper than the factory-positioned breather. Yet they put it there anyway. So if the breather mod is necessary, the design is fundamentally flawed, and if modding the cap itself is also necessary, that’s an even deeper flaw.

Don’t get me wrong, I’m not saying the OP is wrong, more just thinking out loud in response to my innate reluctance to distrust those whose function it is to build a solid and reliable vehicle. On the other hand, Ford built exploding Pintos and the current loophole in helicopter fuel system crashworthiness that has needlessly killed and maimed countless people indicate that it does happen.

That's a very wise thought process you have there. I typically apply that to fluids, replacement parts, and greases.

I sincerely doubt Toyota engineers designed every 4runner to do the most extreme off-roading. I still can't get a snorkel made, even aftermarket, for this truck. They do need to balance their appeal between yoga pants and mud haters, yuppies and country folk.

No manufacturer is going to design a mass production vehicle capable of fording 48 inches of water. They likely know that if you're going to do that, you'll regear your differentials, run 35's or better on a minimum 3 inch lift, and install a snorkel and other scuba gear.

They install running boards knowing that those who want sliders will install sliders later.

I'm sure they recommend you don't submerge your rear end, but a few of us will do it anyway.

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[Runn4est]

Hmm. The only reason I’m a bit bothered by this revelation is because I literally just ordered (2) new breathers (the front ones with the barb fittings) right before seeing your postings about this. I wanted to replace the engine bay one anyway since it was all rusty and messed up, so I figured this was a good excuse to get one to relocate the rear at the same time. Had I known this, I may have just ordered the front one, and used one of the old style sintered bronze breathers at the end of the hose in the rear. In hindsight, I probably should have done that anyway since as has been mentioned, if you submerged the height of your gas cap, you have bigger issues anyway!

The front breather's are 2-way.

 

[Bluesky 07]

That's a very wise thought process you have there. I typically apply that to fluids, replacement parts, and greases.

I sincerely doubt Toyota engineers designed every 4runner to do the most extreme off-roading. I still can't get a snorkel made, even aftermarket, for this truck. They do need to balance their appeal between yoga pants and mud haters, yuppies and country folk.

No manufacturer is going to design a mass production vehicle capable of fording 48 inches of water. They likely know that if you're going to do that, you'll regear your differentials, run 35's or better on a minimum 3 inch lift, and install a snorkel and other scuba gear.

They install running boards knowing that those who want sliders will install sliders later.

I'm sure they recommend you don't submerge your rear end, but a few of us will do it anyway.

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I appreciate your thoughtful response and especially that you didn’t take offense. There are some hair-triggers around and you never know what’s going to set someone off.

Your take makes sense. My next question would be whether the depth needed to submerge the factory breather falls within Toyota’s definition of a typical water crossing (if they use such data).

(This is a tangent but I would be absolutely fascinated to learn the inside story of how vehicle specs are determined. Any kind of behind-the-scenes stuff like that is interesting to me. For instance, there was a guy in a Land Cruiser at the Kentucky Toyota Trail Ride who works for the Toyota division that designs and installs interiors. They do work for a surprising range of clients ranging from other automakers to aircraft manufacturers and hearing about their operation was a nice bonus on an already awesome day.)

At the end of the day, any mod like this one comes down to risk + expense + time vs. reward. Water crossings like the ones in the Kentucky ride (they start 3:52 into the video) make me glad I did the breather mod. Those are as extreme as I’m likely to get into so I’m comfortable not pulling the breather back out to remove the plug.

With that said, always ready to consider other opinions.

Good discussion here.

 

[Rodtheviking]

I cannot think of a reason why the rubber seal would still be necessary. By the time water would get into my breather up there I think I'll be parting the truck out.

Use your head, this seems like exactly what ARB sells, but I'm no expert.

There is at least one member here that doesn't believe there would ever be a situation in which a vacuum is created, that member also doesn't believe that this rubber piece creates a one-way valve. Maybe someone far more knowledgeable could chime in on this.

anybody have a spare axle that wants to do some science??

This was exactly my thought, if it gets up that high I'm screwed anyway. And besides I did an ARB dif breather kit on my old Discovery and it worked fine.

 

[Terminator03]

The front breather's are 2-way.

That is great news, thanks. I don’t have the parts yet, as I just placed the order yesterday, so I wasn’t sure if it was different, other than a barb fitting in place of the threaded type for the rear.


For those who are discussing submersion, it’s not only deep water crossings that this is important for, in some cases launching boats, the rear can get into the water at the height of the stock breather. I’ve personally never had that happen yet, but do know someone who got water into the rear ended that way.

 

[cloud]

The front breather's are 2-way.

I'd be interested to find out how you know. Mine looks exactly like the rear. Although once I modified it, the rear still appears the same as it did before.

Have you disassembled the front breather?

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[cloud]

That is great news, thanks. I don’t have the parts yet, as I just placed the order yesterday, so I wasn’t sure if it was different, other than a barb fitting in place of the threaded type for the rear.


For those who are discussing submersion, it’s not only deep water crossings that this is important for, in some cases launching boats, the rear can get into the water at the height of the stock breather. I’ve personally never had that happen yet, but do know someone who got water into the rear ended that way.

Hmmm. I never thought about boat launches. Id imagine engineers absolutely considered that in their designs, but at the same time I've always tried to keep tires out of the water because ramps are usually slick where they're underwater.

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[Runn4est]

I have not disassembled it, but I have installed the OEM front breather part 90930-03136 (instead of 90930-03031) on my rear diff, extended to the fuel door. I did the good ol suck test prior to install just to make sure haha.

You will also need the union part 90404-51319 for install directly into the diff.