<VV> Diff Still Blowing Lube Out Vent

[Richard Widman]

I didn’t pay much attention to the vent when I had mine apart, and if I was
near the differential and parts right now I’d pull the cover back off to
look more closely at the vent.  But let’s look at theory for a moment.

First, the gear oil should be at a level where it begins to lubricate all
parts when cold, but when expanded by heat it does not get too high to
create foam and cavitation.

The vent is there to let off air pressure when the gear oil expands with
heat.  The only oil that gets there should be by splashing.  If the vent was
not there, the pressure would go out the seals, taking fluid with it and
bringing in water if it was being cooled by going through high water (normal
here).  So its sealing pressure should be less than the seals.  As I
remember last month when I had mine apart, it is just the weight of the cap
that pushes it down to seal.

I see three solutions to this:

1.  Put more weight on the cap.

2.  Put a spring on the vent that gives it a little more tension and check
to make sure that it is sealing when closed, not a rough surface that does
not seal.

3. Remove the vent and replace it with a tube, not like shown in that
picture, but similar to what comes (or came on my 93) on Grand Cherokees and
Nissan pickups (at least here).  The Grand Cherokee comes with this fitting
and a rubber tube that goes up to the engine compartment.  No way for water
to get in or for fluid to splash out.  I think the hose is optional in the
Nissan, but I use their fitting to replace the lousy vents in Toyotas, then
adding the tube.  The other end of the tube can be clipped anywhere higher
than the differential. I like the engine compartment, although I once found
an idiot that connected the differential vent from a Grand Cherokee to the
overflow tube on the radiator. Murphy’s law.  In Toyotas I’ve put them over
the wheel opening and in engine compartments.  In a Vair you could just run
it up the side of the firewall.  No need for a cap or filter on the end, as
the oil vapors in the tube act as an excellent trap for dust.  Don’t need
anything big, even a ¼ inch hose is plenty.

 

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Richard Widman

 <http://www.widman.biz> www.widman.biz