Originally Posted by Dualsportist
Actually, I don't plan on ever using the zerks on my trailer's hubs. I have seen the pnuematic pressure of grease and I know of no known seals that will withstand the pressure required to push old grease out of old bearings.
There is little pressure required, unless you are trying to grease them in sub-zero weather. The bearings are open to the outside of the hub, so the grease just flows through the rear bearing, filling the center cavity, then out through the outer bearing.
Of course, the warmer the grease the better.