The short version
- Two different systems get confused. One adds grease, the other keeps water out.
- A spindle fed axle pushes grease from the inner bearing outward through a hollow spindle.
- A bearing protector cap holds about 3 psi of positive pressure so a cooling hub cannot suck water in.
- Most spindle greasing horror stories come from not turning the wheel while pumping.
EZ Lube and Bearing Buddy do completely different jobs, and the confusion between them causes real damage.
EZ Lube is a lubrication route. A bearing protector is a pressure device. Fitting the second does not give you the first.
EZ Lube and Bearing Buddy do opposite jobs
The spindle is drilled, with a grease fitting at the outer end. Grease enters there, runs down the center, and emerges behind the inner bearing.
From there it is meant to push forward through the inner bearing, across the hub cavity, and out through the outer bearing.
That path only works while the bearing is turning. A stationary bearing is a wall of packed grease and rollers, so new grease takes the easier route.
The failure everybody describes
Pump into a stationary hub and pressure builds behind the inner bearing. The seal lifts and grease goes into the brake drum.
Contaminated shoes cannot be cleaned back to usable. That is a brake job on top of a grease job.
The manufacturer instruction addresses exactly this. Lift the wheel clear of the ground and turn it by hand while pumping slowly.
Rotation opens the path through the bearing so grease follows it rather than forcing the seal.
Doing it the way it is meant to be done
- Jack the wheel clear and support the trailer properly on stands.
- Remove the rubber plug in the cap to reach the fitting.
- Use a hand gun, not an air gun, because the pressure needs to stay low.
- Spin the wheel while pumping, slowly, one lever stroke at a time.
- Stop when clean grease appears at the outer bearing, and not a stroke later.
A disturbed seal is much easier to push out than a settled one, and this system relies on the inner seal holding.
Seals are inexpensive, and why they matter is on the seals page.
What a bearing protector cap does instead
This is the spring loaded cap on the end of a boat trailer hub, and its purpose is pressure rather than lubrication.
Behind the visible face sits a piston on a spring. Filling the hub pushes that piston out slightly, and the spring then holds gentle pressure on the grease, in the region of 3 psi.
A hot hub entering cold water cools fast, the air inside contracts, and water gets pulled past the seal.
A hub already held slightly above outside pressure has nothing to pull. That is the whole idea, and it works.
Why the launch is the dangerous moment is on the marine grease page.
Reading and filling a protector cap
The visible piston is a gauge. Press its edge, and if it rocks or moves slightly the hub is correctly filled.
A piston sitting hard against its stop with no movement means the hub is overfilled. Most designs include a relief that vents rather than forcing the seal.
Pumping grease in does not remove water, metal particles, or grease that has already broken down. It just adds volume.
The hub still has to come apart on a schedule so the bearings can be seen and cleaned.
The full procedure is on the repacking guide, and how often is on the intervals page.
How much pressure the gun itself is capable of is on the grease gun page.
What a yearly service still has to include, fitting or no fitting, is on the page about RV repack intervals.
Common questions
How does an EZ Lube axle work?
Grease enters a fitting at the spindle end, travels through a drilled passage, and emerges behind the inner bearing to push outward.
Why did grease end up in my brakes?
Almost always because the wheel was not turning while pumping. Pressure then lifts the inner seal instead of following the bearing path.
Can I use an air powered grease gun on an EZ Lube fitting?
No. Use a hand gun with slow strokes. High pressure is precisely what pushes the inner seal out of the hub.
Are EZ Lube and Bearing Buddy the same thing?
No. It is a spring loaded cap holding around 3 psi inside the hub so water cannot be drawn in as the hub cools.
How do I know a protector cap is filled correctly?
Press the edge of the piston. Slight movement means correct. No movement at all usually means overfilled.
Do EZ Lube and Bearing Buddy replace repacking?
No. Adding grease does not remove water, debris, or degraded grease. The hub still needs to come apart periodically.
Should I fit new seals before using the fitting?
If the hub has been apart recently, yes. A disturbed seal pushes out far more easily, and the whole system depends on it holding.