Using a grease gun to grease wheel bearing has always been, despite Bearing Buddy and all the other's claims, a poor way to grease wheel bearings. The problem is that as Jim said, the entire cavity must become filled before grease reaches the far bearing. From then on, each time more is pumped in, what greases the far bearing is the old grease that's been drying out in the hub cavity. Far better to go the extra mile, remove the hub, and hand pack both bearings, allowing you to actually inspect the bearings for rust or other damage. Seals are cheap and a new one at the same time assures water and dirt will stay out until the next time you service the axle. Pumping grease in until it oozes out also runs the risk of dislodging the seal. In addition, with the cavity fully packed with grease, as the hub warms up, grease and trapped air will expand pushing more grease out making a mess of the inner sidewall of the tires (and brakes) and causing confusion as to whether the seal is really bad. Properly hand packed bearings and fresh seal will result in clean tires and a timely warning (leaking grease) if something is amiss with the axle. A real problem is that adjusting wheel bearings is becoming a lost art. Most upcoming mechanics are only familiar with sealed bearings now that virtually all autos and most trucks are equipped with sealed bearings on all four wheels. You can read all the books you want but nothing takes the place of an experienced mechanic teaching you by letting you feel the difference between too loose, too tight, and just right bearing adjustment. Sadly many current wrench turners never got that memo.
