Question about diff breather mod - why 2 way?

Been getting ready to do the diff breather mod on my 2010, but I noticed that the OEM breather on the diff is a 1-way, and the one people are replacing it with at the end of the hose is a 2-way. Doesn't that introduce the possibility of getting contaminants down the hose and into the diff by using a 2-way always open breather?

 

"One way breather" is a misnomer. It's just called that because it's supposed to filter water and contaminants out when it's letting air into the differential. Your differential is not vacuum sealed. Air is constantly flowing through the breather in and out of the gearbox.

It's always been a 2 way- that's the function of breathers- let hot air vent when the diff heats up, allow air to flow back in when things cool down.

The breather mod that you've seen (adding a hose to the breather to raise the air inlet/outlet location) just buys you additional insurance in case you're driving through high water. The problem I see with some of these write ups is they don't include adding a filter to the end of the hose.

 

Umm... not so sure about that...

The breather on the diff. is ONE WAY... lets hot, expanding gasses out when pressure inside the differential is greater than the force of the spring in the breather/ check valve.... Otherwise it is normally closed at 0 or negative pressure... so nothing is allowed in.

The contamination occurs when you drive into cool water with a hot differential when off roading... and the water and mud can suck into the differential past the axle seals.

Using a TWO WAY breather, up high allows the hot gasses to escape, and allows cool air to return to the differential during a water dunking. This is a vacuum breaker, like on a sprinkler system... at the high point so mud won't suck into upper sprinklers as water drains out of lower sprinklers. Put your thumb over a straw, and you can pull water up, out of a glass of water. Take the thumb off the straw (allow air into the straw) and the water can't stay or get into the straw.

This is my understanding and since my new Tacoma differential was contaminated after a muddy water bog crossing in Baja, I know it can happen.

 

The above is not correct. The ONE way breather will not allow air back in. When you hit cold water it creates a vacum and water is pulled in from the axle seals. Without the vacuum air pressure normalises. Put a one way breather on extended lines and you still pull water from the axle seals. The one way valve itself being low is a non issue as that is not where water enters... and yes, water can get in from the relocated 2 way filtered breather, but the one way only needs submersion to the axle seal to suck water.

Crap.. my keeyboard is jaccked so someone beat me to it

 

If you extend the breather long enough (using just a regular air hose) and put it up high enough into an area that won't get hit with water or dirt, just slap on the stock breather end and call it good. You don't need a filter and you don't need anything special.

On my 96, I ran my rear diff breather the whole way to the engine bay. I *T'd* the front into it and the end of the breather sat next to the clutch resevoir.

 

No, no crap... it is good to have several confirm what I typed, and I appreiate it!

 

Yes... the breather has a tiny opening... and more than likely the air in and out will always be what is in the five foot section of tube... I put the breather in the truck bed side storage compartment... It is protected and too high up for water to get in. Others have located it in the gas filler bay or behind the brake light lens or the open tiny compartment in the bed.

My breather install photos are in the link in my signature, below.

 

Also, remember the two way valve is what Toyota use's on the front remote breather, I'll follow their lead.
Why they didn't do a remote at the rear makes no sense.

 

X2 (specially on the Off Road TRDs)!

 

OKAY! Now we're getting somewhere with some learning! (you guys are awesome).

So it would seem that if the axle seals are pulling in water in a dunking because the OEM 1-way breather suddenly snaps shut creating a vacuum, that Toyota didn't create a very good offroad design!

So everyone is adding a 2-way higher up. But what about a filter as TX Tacoma mentions? I drive down a lot of dusty dirt roads. Whether I put the new breather in the gas cap bay, in a side compartment or high up in the fender well, it's going to suck dust into that hose. Is there a filter that can be added? Seems to me that not pulling water into the diff is a good thing. But so is not pulling in granitic dust!

I believe I read somewhere that if you put the OEM 1-way breather at the end of the hose, that it still snaps shut when the diff gets dunked and cools off rapidly, but that this 5 feet of flexible hose is enough to overcome the vacuum problem at the axle seals because this hose compresses instead. Anyone confirm this?

 

Your TRD OFF ROAD has a remote two way breather up front now and you drove through all those same conditions, Are you going to put a filter up front also

 

One of the TW'ers put a fish aquarium stone (the kind that bubbles out air) on the end of his tube. Another put a mini K&N looking breather filter... which is cool.

I did what most did, and what Toyota does... put the two way breather at the end of the tube... The opening is tiny and you could wrap a filter cloth around it, if your dust will be that intense! Sounds like a Baja scenario?!!

 

"One way breather" is a misnomer. A breather breathes: breathes in, breathes out.

If your differential "breather" is not actually a breather, but rather a one way check valve for airflow, then you are correct in your contention that your differential and axle tubes are under a perpetual vacuum and will seek to pull contaminants through the axle seals for the life of the rear axle.

I do not argue that the gearbox will develop a vacuum when the hot air being expelled causes this condition during operation. I argue that the vacuum in your diff is not perpetual, nor is it designed to be alleviated by airflow sucking through the axle seals. In my years of aircraft gearbox and transmission design, creating negative pressure across external seals and expecting them to do their job is what we call a pisspoor design. I give Toyota more credit than that.

 

someone actually suffered DAMAGE from not doing the breather mod??

 

Maybe it already has one inline. Do you know?

 

No not for a fact.
Maybe this calls for a internet bet, I bet it does not .

 

Yes, if I didn't have the gear oil replaced soon after the trip, me... and anyone who goes into water more than 18" deep (that covers the differential)!

 

I agree it isn't really a breather... unless you call something that exhales only, a breather! I removed it off the differential and easily blew out through it with a small amout of resistance from the spring... But, the second I tried to reverse the air flow (ie. suck air through it) it closed. So no air or water can be drawn into the differential through that 'breather'. It must get contaminated through the axle seals.

 

I think you're over-complicating things.

The diff breather is just an opening that prevents pressure from building up in the diff. It's not a closed system even if the thing is shut. There's nothing scientific about it.

It's not any different than putting a pan of water on the stove with a lid just resting on top.... when the water boils, the lid lifts up slightly to let out the steam.

 

Well I know that. But the difference is when the diff is cooled, the 1-way shuts. When the diff is cooled with a 2-way, it remains open potentially allowing debris in. Obviously sucking water through axle seals is a problem. But so is any contamination.