No. 5 – You can overfill a bearing protector

Bearing Protectors

Bearing protectors

Bearing Buddies® or similar bearing protectors are almost a standard feature on boat trailers. While some people claim that bearing protectors are a scam, a large proportion of boat trailers have them installed.

Why do people want them?

  • Trailer wheel hubs and roller bearings are packed with grease. They are protected from the elements by a grease seal on the side facing in, and a metal dust cap tapped into the end of the hub on the side facing out.
  • Problems come up when the bearings get hot. The grease expands, and when hot hubs meet cold water, the grease contracts, possibly pulling some (salt) water into the hubs. Repeat the cycle often enough, and you can wind up with contaminated grease, and corroded or seized bearings.

Bearing protectors were developed to help prevent these problems. They replace the metal dust cap, and are made of a heavy metal barrel with a flat steel disc inside, and a spring to keep the disc pushed back into the barrel. The disk has a grease zirc in the center.

In use, the bearings and hub are packed with grease, and the bearing protectors tapped into place. A small amount of additional grease is pumped into the barrel thru the zirc. The grease partially fills up the protector, pushing the disc out, and compressing the spring.

When the grease expands, it forces the disc out, further compressing the spring. When the grease cools and contracts, the spring pushes the disc back, keeping it in contact with the grease, and preventing water from getting sucked into the hubs.

So what can you do to screw this up? Overfill the bearing protector. If you put too much grease into the protector, the spring becomes fully compressed. When the hub gets hot, there is nowhere for the expanded grease to go, except out a small weep hole on the barrel, or out the back grease seal. Once the rear grease seal is compromised, it becomes a very easy way for water to get into the hubs.

You can tell if you’ve gone too far by trying to wiggle the disc. If the spring is fully compressed, and you can’t wiggle the disc, you’ve gone way too far. Another bad sign is if grease starts coming out of the weep hole when the hub is cold. To fix the problem, the bearing protector has to be removed, and some grease scooped out.

Another point – bearing protectors usually come with plastic caps to cover the ends. We’ve stopped using them. They are not watertight, so when they get hot and are then dunked in water, they can suck water inside the cap. This traps water against the springs, causing them to rust.

If you do use the caps, make sure you remove them once you’re back in the garage so you can check for trapped water.