I know this is an older post, but I'll stir it a little. This bearing lube system seems to be controversial at times.
For those of us with the "Ultra Lube" or Dexter "EZ Lube" system. I do not use that bearing lube system. The EZ Lube has a grease fitting in the axle center and feeds grease between the back seal and the back tapered bearing. The grease can blow the back seal out or it will fill the hub completely with grease. Either is not good. It goes against all the sealing and lubrication technology I was taught (37+ years in industrial maintenance and talked to lubrication reps). If used as a standard axle, it's fine.
Some YouTube research into the EZ Lube system to watch.
DEXTER TV - Dexter Bearing Maintenance
www.youtube.com/watch?v=GnH-h3W9XvINotice the Dexter guru hand packs the bearings. He is not using a grease gun to fill the hub. So why doesn't he use the lube system, if they are telling you to use it?
A couple of issues: The "expert" uses a wood block (should be clean aluminum or brass) and hammer to install the back seal. Dirt falls off the block with the first hit. You've now got dirt in your hub and maybe wood splinters. He does not lube the spindle before installing the hub. You don't want the seal running on a dry surface and it installs with less chance of seal cutting.
We need to understand that when you heat up just about anything it expands, be it metal, glass, plastic, or grease. We need to agree that the back bearing seal is not a pressure seal. It has two functions- to keep grease in and contaminants (dirt and water) out. Most rear seals are a double lip seal with a tiny spring on top of the seal area to keep it in contact with the spindle surface. Also, for anything to flow there has to be a pressure difference. On the Dexter video, it states not to use a pneumatic grease gun because it pumps too fast (which really means it is generating too much pressure). Even the cheapest manual lever grease gun can generate 3,000 psi. Some manual grease guns will generate 10,000 psi, per Grainger's web page.
Ok, so now we pop out the rubber plug to expose the Zerk fitting. Grease gun is snapped on and you start pumping. If there is grease in the hub that is several years old, or the guy doing it has never seen the EZ Lube video and does not jack up the camper and spin the wheel, then what? The back seal can be unseated allowing what to enter? I never saw the back seal area cleaned and I doubt it ever does get cleaned, unless you pull the hub. So as the pressure drops and the back seal reseats, what is it pulling in with it? Grease + grit = lapping compound. Far fetched? Maybe. OK, the pumping is finished, the grease has pushed through the back bearing, filled the hub completely, and pushed through the front bearing. Pop the little plug back in and you're good to go. This is March and you are ready for June now. Things have warmed up like the air temperature, sun is out, and the roads. It also means all that captive grease is warming up, also. You hit the road, with your grease packed hub / roller bearings and what is happening inside the hub? The roller bearings have to push grease out of the way to turn, but it has no place to go. It is sucked back into the "lower" pressure area behind the roller bearing, only to be displaced by the next roller bearing. These are not ball bearings, with nice smooth surfaces. These are roller bearings, with square ends and bars for retainers between the rollers that is preventing the flow of grease. To say there is a greasy turmoil going on in and around the bearing, is an understatement. You have massive struggles going on. Lubrication in this application should take place as a film, not a bath. I would not be surprised that at times, the rollers may be sliding between the races without rotation. In an extreme case, with all this heat being generated, the grease expanding, the grease will probably pop out the little rubber plug to relieve the pressure or blow out the back seal. The grease has to go somewhere. Blowing out the back seal can grease your brakes, which is not good for stopping.
Look up some YouTubes on people "repacking" the bearings for the first time with this system. I find it interesting that the EZ Lube system does not come full of grease from the manufacturer. People have to use almost a full tube to fill the hub void between the bearings. Why? Because it's not needed, and the manufacturer doesn't want to buy all that grease either.
Just because an item made it to market, doesn't mean it should have. Think of particle board, ScotchLoc electrical connectors, Pet Rocks, etc.
Note on bearings: At stops while towing, check the hub temps with the back of your hand. If they are close to ambient air temperature, or a little warmer due to stopping, the bearings are happy. As little as most campers are used, bearings should be good for years, if installed correctly.
This is a low-speed application for roller bearings. Even 8" tires (16.1" diameter) are not turning that fast (at 60mph, they turn less than 1,300 rpm).
Note on Zerk fittings: Even if you "clean" the Zerk fitting off, you're still pumping fine grit in with the first pump. This mostly applies to exposed Zerk fittings on stuff like suspensions and universal joints.
Note: At work, a new mechanic greased a machine, with two 120mm ID tapered roller bearings on the drive shaft, doing a preventive maintenance check list. It started fine, but after a couple of minutes started to slow down to a creep. This machine was driven by a DC drive, so it was doing all it could to maintain the set RPM. When the drive checked out, we went deeper. When the Zerk ball was unseated with a small screwdriver, grease shot out like a bad zit. We had to bleed the grease off several times that day until enough got out to not cause an issue.
