sealed diff "breather"

[taslucas]

Just extended my front diff+transmission breather and put a cheap fuel filter on it as im sure lots of people have done. A question came to mind, I'll try to explain it as best i can: as the air in the diff heats up, how much volume needs to leave the diff to keep the inside pressure low enough? I was thinking that if you were to block the end of the fuel filter then the volume of air in the metre or so of tube plus inside the fuel filter might be enough to accept the expansion of air from the diff.....?
Does that make sense?
and if it was, then you could have fully "sealed" diff breathers......

[taslucas]

sorry Mods, i think i should have put this in the general mechanical.....Feel free to move it:)

[growler2058]

The problem is that if your diffs are hot and you hit cold water the sudden contraction can draw water past your seals. So i dont rekon a sealed system would work

[AB]

x 2 with growlers sudden contraction hot to cold scenario you would definitely require an open breather. Not sure what would actually happen if it was completely sealed and it tried to contract with no breather. I would imagine that it would try and draw air from the weakest points and do damage.

[NissanGQ4.2]

The problem is that if your diffs are hot and you hit cold water the sudden contraction can draw water past your seals. So i dont rekon a sealed system would work

x 3, sealed system will not work

[flemj]

Hi Guys,

What might work but is impracticable would be a balloon type system. You blow it up and when the diff hits the water it draws air from the balloon or when it gets hot the balloon gets bigger.
Not something I want under my bonnet

John

[growler2058]

Would need to be tuff material but woulkd work i spose

[GRA.GU]

You mean like this? http://locktup4x4.com.au/universal-118/differential-215/diff-breather-kit-1176.html

[taslucas]

x 2 with growlers sudden contraction hot to cold scenario you would definitely require an open breather. Not sure what would actually happen if it was completely sealed and it tried to contract with no breather. I would imagine that it would try and draw air from the weakest points and do damage.


But when you think about it, if it's sealed when it's cold then it has the right volume of air in it. As the air warms up it expands but does not escape, so when the diff suddenly cools there is still the right volume of air there already. That theory obviously doesn't work for the small amount of air that's just in the diff housing but with the added volume of tubes and a container of some sort, maybe it would be sufficient?
For simplicity lets say the diff breather was attached to a sealed 20lt drum, that would have to be enough extra air volume to stop the diff sucking water past the seals?
Now continue to make the sealed container smaller until theres just enough volume to still work.

[GRA.GU]

Agree with your thinking and reasoning, taslucas, except on the point that if its sealed when cold it will still have the same amount of air in it. That's the point, it's not really sealed, the air can leak in and out.

The link that I've put in above overcomes those issues with the bellows arrangement, but I'm not really advocating that device as I suspect it may be vulnerable to damage by stray sticks, although to some extent so are my rubber tubes.

Cheers.

[04OFF]

I think a large but sealed reservoir would help, but only because it will increase the time it takes to heat the air in the diff housing, because there is just more air to heat, if the whole system is sealed, heat will still make the air expand, and create some positive pressure in the whole system.

Regardless of any water crossings and sudden cooling, diffs have breathers so this added pressure can escape easy, instead of pushing/blowing past seals causing leaks, cars never designed for off road still have diff breathers to protect seals in this way.

[taslucas]

Thanks for all the replies guys. Was just thinking out loud really, lol thanks for humouring me. Your right though, they have breathers for a reason. Mine are now right up out of the way:-)

[Sir Roofy]

but when you think about it, if it's sealed when it's cold then it has the right volume of air in it. As the air warms up it expands but does not escape, so when the diff suddenly cools there is still the right volume of air there already. That theory obviously doesn't work for the small amount of air that's just in the diff housing but with the added volume of tubes and a container of some sort, maybe it would be sufficient?
For simplicity lets say the diff breather was attached to a sealed 20lt drum, that would have to be enough extra air volume to stop the diff sucking water past the seals?
Now continue to make the sealed container smaller until theres just enough volume to still work.

but why do you want to seal off the breathers ,are youn contemplateing going snorkleing in the gq

[taslucas]

but why do you want to seal off the breathers ,are youn contemplateing going snorkleing in the gq

Lol, it gets wet here! Nah it was just a thought really.....I like to know why things are done, not just how to do them.

[Sir Roofy]

lol, it gets wet here! Nah it was just a thought really.....i like to know why things are done, not just how to do them.

good enough all i know is you enter a crossing with hot diffs
and whamo you get a gut full of water or worse crack the housing

but when you think of it the breathers arnt very big normaly ,what 1/2" high with a little cap on top
so your theroy might work

[taslucas]

good enough all i know is you enter a crossing with hot diffs
and whamo you get a gut full of water or worse crack the housing

but when you think of it the breathers arnt very big normaly ,what 1/2" high with a little cap on top
so your theroy might work


Standard ones on the GQ are a bit bigger than 1/2 inch. I have a picture in my members ride thread if ya want a quick squiz:-)

[Dr Gary]

My previous Patrol (GQ) managed to suck water through the axle seal with factory breather, and it had only 25k on the clock. Crossing shallow water at Roper Bar, so I suspect any restriction would be problematic

[taslucas]

My previous Patrol (GQ) managed to suck water through the axle seal with factory breather, and it had only 25k on the clock. Crossing shallow water at Roper Bar, so I suspect any restriction would be problematic

That's no good, are you sure it didn't splash up into the breather?

Lucas