Here's why I think leaks are unavoidable: Since you pump grease into the hubs
when the wheels are not rotating, the bearing is filled completely, including
the spaces between the rollers. Once the wheels begin to turn at speed, the
rollers clear a "path" of open space through which they travel. That volume
of displaced grease has to go somewhere - it can push back the piston in the
bearing buddy or it can ooze out the lip seal, or both. Since lip seals are
intended to seep just a little (the seepage is what lubricates them and keeps
them from wearing out quickly) the overfilled hub is very likely to leak at
the seal as long as there is much positive pressure behind it.
The fact that the hubs are stuffed as full as they can be with grease means
that there isn't much room left for water. The lip seal and bearing buddy
should have lots of protective grease blocking the entry of water.
If I understand the Spindle-Lube axles correctly, they should work in much
the same way, allowing the hub to be filled completely. The difference, which
may help them to leak less or not at all, is that the "old" excess grease is
allowed to flow out and is not held in the hub under spring pressure the way
it is with the buddies. If the wheel is spun a few times before the "exit"
fitting is closed, the hub should end up with just the right amount of
grease. The fact that the grease is so easy to change is also a big plus -
they just need to figure a way to get that old grease to go directly into my
garbage can without me having to touch it!
As an aside, I once tried filling the trailer hubs completely with grease
with the bearing buddies, then removing the buddies and putting on the
regular caps (thinking they'd be better at keeping water out). It was
impossible to install the caps. As I tried to tap them on, they would push
right back, sort of a "hydraulic lock".
Dave Kautz
P-15 #1632 Tilly Lucy
Palo Alto, CA