maat
yeah nah maybe
ok mate
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.... but don't try to trivialize my point of view with stupid pictures.
Probably both of us.And I thought that pic was aimed at me
Yes... Oil will lube the seal lips better. (Damn ... a point conceded )
But as for the breather argument, diffs have far greater need for a breather because there is so much more trapped-air inside.
And no matter whether your hubs are vented (to some safe level) or not, if you submerge them you are always likely to get water ingress because the pressure differential from depth-of-water is the main driving force.
So I suspect "hub water ingress rates" would vary very little between "vented" and "sealed" setups.
(Who's going to run out of breath first in this? ......................)
And think how travelling on steep side-cambers will tend to fill the hub on one side while draining the other one ...
The pressure difference from submersion is one factor and a relatively constant one. A foot down you'll have about half a psi. That's pretty minor.
What does make the difference is whether the inside of the hub cavity is at ambient pressure (0psi) or pulling a vacuum (-5psi wouldn't be impossible).....
...My rangie hubs take maybe 200cc each max. But draining them takes forever. On a side-slope you can't get much oil out the high side (the protruding stub is the only exit and it gets higher the more you lean over) and the low side has an air-lock preventing it completely filling.
When you take an oil hub off, they'll drip into a try for days. All those cavities in roller bearings are great at holding oil. Accidentally running them dry isn't a concern I've ever had.
When a warm hub gets immersed in cold water the metal housing actually contracts in size as it get cooled which by itself would actually tend to compress the air trapped inside. (True that this is effect is pretty negligible, but your -5psi figure above is just "plucked from the air" so it deserves an equally-dodgy counter argument Dougal. )
But there is more to my armoury..
To get the "vacuum" you talk of, the trapped air must be cooled and this process of transferring heat from the air to the cold hub metal takes much more time than the transfer of heat from the hub-metal to the water. So a short water crossing is unlikely to produce anything measurable as far as vacuum goes (in a grease-lubed hub)... whereas someone getting stuck in a boghole or during a river crossing is a completely different story.
And let's look at that more deeply. (Excuse the pun.)
So when someone has been stuck for 10 minutes in the middle of a river do you still think temperature difference would be having the major effect?
At that point, the trapped-air temperature won't be far off the river temperature!
In this scenario the absence of any vent tubing (to vent an OEM grease-filled hub) gives it the advantage that for more water to enter, an equal volume of air needs to escape past the seals. In other words, the lack of a vent tube is actually restricting the rate of further water ingress here.
And one final point (because hopefully I'll resist any further additions to this thread) ... Early 40-series cruisers have their handbrake shoes located right next to their rear-drive output oil-seals on the transfer cases. Surely no-one can argue that the performance of these brakes are seldom harmed by oil leaks?
My handbrake (designed like this) normally performs admirably but I am always aware that when I need it most (such as on extremely steep bit of track when I've lost traction and found I'm really in the sh#t ) some oil will inevitably tip off a seal lip (or wherever) onto the linings and make it barely hold (even when the braking action of the shoes are being backed up by having the transmission in low-ratio 1st and I've turned my engine off to get out and pull my hair out).
So I still thank Mr Toyota for making sure none of my other brake linings are so close to oil seals!
Yeah fair enough, lets calculate it then.
We all know PV=mRT.
Rearranges to P=mRT/V.
If we are holding volume, number of molecules constant then the only variable is temp.
This comes down to change in P is proportional to absolute change in T.
Take an axle running at 50C (323K) and put it into water at 10C (283K).
The change in pressure will be the ratio of 283/323 = 0.876.
If we started with 101.3kPa or 14.7psi (atmospheric) then we'll now have 88.7kPa or 12.8psi.
A bit under 2psi vacuum from a change in temp of 40C...
...The volume of air inside a hub will reach the metal temp within seconds. ...
.. Any river crossing I've done takes at least 10 seconds and will do that. You've then pulled the vacuum above and unless your seals can sustain the 2psi then you'll bring in water through the seals to minimise the vacuum.
Venting the hubs above the water line will remove the vacuum and prevent the problem. Oil bathing the hubs connects them to the main axle breather which also prevents the problem....
...Landrover does the TC mounted drum-brake hand-brake too. They have an oil catcher inside so when your rear TC oil seal leaks it is drained out and can be seen dripping off the backing plate behind.
I did mention earlier I've had oil soaked brakes before. The vehicle still stops, braking capacity is reduced by a bit under half (only one brake gets wet) and the vehicle pulls under braking.
It's not the immediate certain death that many assume it'll be.....
OK Couldn't resist one more post ...
Ahhh.mmmm (Clearing throat....)
So with ideal-situation maths, hot-to-touch hubs, and pretty-cold water you now calculate a value less than half of your earlier "wouldn't-be-impossible figure" of 5psi Dougal
Heat exchanger manufacturers go to a lot of trouble to extend surface area when trying to carry heat to/from air. Yet you say a smooth hub surface covered in grease achieves such a great result? That's truly amazing!
Hubs represent a small volume. So it stands to reason that pressure difference caused by temperature change can be eliminated by similarly small volume changes. And taking this further ...If a degree of vacuum starts to develop, it probably gets reduced or even eliminated just from the flexing of the seal rubber. And when you have a double-lipped seal (as we have) any vacuum will tend to make the outer lip "pull-in" to create an even better seal to stop water ingress.
Whatever Landrover did, Toyota did better... (for similar vintage)
Wayne? Are you out there? Am I doing alright? (I'm wasting too much time here... so I need someone else to take over..)
fok mense, kry 'n bitjie lewe