Many Massey Ferguson farm tractor front hubs have the same system Neil has devised, but they are low speed. The advice about watching blowing out the inner seal is true. I would be careful about it on a duece because then it can get into the brakes if the inner seal is turned inside out by the pressure that can be put out by a grease gun. I note that Neil has two fittings on the cap, is one a pressure relief to limit the pressure applied by the grease gun to a safe level? Yes, the hub has to be full of grease for it to work right. Heat and resulting pressure could build up at prolonged highway speeds. It works on boat trailers, which have a spring in the cap to regulate pressure. If the second fitting on Neil's cap is a spring loaded pressure limiter, then the excess would be vented there. It might get onto the sides of the trailer, but that is better than inverting a seal from the pressure.
Properly hand-packed bearings will run many miles with no problem. I have always been amazed by how little grease they demand. Moisture getting into the grease, or incorrect grease is the biggest culprit in failures.
Regards Marti
