Dust caps are considered “the basics” of bearing protection. Look around the boat ramp and chances are good that half the trailers there have dust caps instead of a more expensive kind of bearing protector. But with their simplicity, dust caps can be high maintenance. These essential parts of your boat trailer keep dust and dirt and water from the bearings inside. But if they’re damaged, and it’s going to happen, every expert will tell you to toss them and get a new set. Dust caps work well, but their real benefit is cost $4-$8 for a pair.
Many BoatUS Trailering readers have written about dust caps coming off. Sometimes, it’s an indication of excessive heat caused by bearing or brake failure.
Caps can come off as a result of damage when removing to check or service bearings or when putting them back on. Experts strongly suggest replacing a bearing cap when bearings are checked or regreased.
There are instances of a cotter pin on a bearing not being properly set after changing hubs, bearings, or grease, and the pin actually touches the inside of the dust cap, eventually pushing it off.
If the bearings aren’t adjusted inside the hub properly, the hub can wobble; this, in turn, causes the castle nut or cotter pin to loosen. When removing a dust cap, jack the trailer tire up so the wheel can spin freely. As the wheel rotates, tap the dust cap from the top of the wheel so that you’re hitting it in a variety of places.
Many suggest using a flat-edge screw driver to do this, which also works (and doesn’t require the tire to be jacked up). If you choose this technique, replace the dust cover.
Quick Tip: Add some grease to the inside of a dust cap. With the dust cap in position over the hub, place a small 2x4 over it and pound in place with a hammer. This sets the dust cap evenly.
Grease is kept around your boat trailer bearings by a seal on one side of the hub (preferably a double-lipped seal) and pressure from from a rubber plug or grommet positioned on the outside of the hub. But there are variations on this technique.
Some modern bearing protectors, such as Tiedown Engineering’s SuperLube is designed so that ant new grease pumped into a zerk fitting in the center of the hub will push out and replace any old grease, which is contained in the dust cap. During routine maintenance, the rubber plug is removed and the old grease can be easily taken out of the dust cap reservoir.
When adding new grease, the wheel should be jacked up so that the tire can spin. New grease is added until old grease flows out of the hub near the spindle. This requires looking at the inner hub while turning the wheel.
It’s important to periodically inspect the rubber cap or grommet for cracks. If these have been in place for a while, or the trailer has been sitting unused for a long period of time, the rubber parts can dry out as a result of sun. Some manufacturers are using a threaded reusable dust cap (Tiedown’s Vortex Lubrication system for grease and the TurboLube system for oil do this).
Because overdoing it with grease can be such a problem, and can have such a bad effecton bearings, while underway, Kodiak Trailer offers the Red Eye Bearing Protector, which is designed to tell you when grease is, and isn’t, needed. When a red washer (the eye) is flat against the housing, grease is added until you can see the “full” mark when the red washer is extended.
These protectors provide 3 psi pressure of grease on the bearings inside, making the system watertight. They can be wasily checked by simply pressing on the “piston” in the center; if it moves freely, the pressure inside is adequate. If it doesn’t, grease is applied until the piston comes out 1/8-inch. Many trailer boaters purchase a “bra,” a protective Bearing Buddy dust cover.
The wood-and-hammer technique used for dust cap removal can also be used for a Bearing Buddy. There’s no need to jack the trailer up either. Just lay the wood against one side of the Bearing Buddy and strike with a hammer. Then place the wood on the opposite side and hit it again. Continue to do this until you’re able to loosen the Bearing Buddy from the hub.
Avoid overgreasing, which can destroy the bearings. Too many times a trailer boat owner will add some grease before every trip to the boat ramp with the idea that “if a little grease is good, a lot is better.” So not true. Continually adding grease adds excessive pressure to the real seal of the bearings so that it blows off. Or, if the real seal holds, the dust cap blows off.
Oil Bath Hubs
The semi you see on the highway is probably running on oil-lubricated hubs. A number of manufacturers including EZ Loader and Ranger use oil-bath hubs as standard parts of their trailers (EZ Loader’s hubs are identified as “Reliable”; see photo).
The upside is this: As the trailer wheel rotates, oil coats the bearings through centrifugal force, in many instances as much as four times for every turn of the tire. Best of all, the oil level can be easily seen by simply looking at the hub.
Not all trailer manufacturers are onboard the oil-filled hub wagon, though. Shoreland’r sent a note to owners two years ago expressing concern about excessive heat buildup in boat trailers using oil-filled hubs when dropped in cold water. The potential exists says Shoreland’r, of creating a vacuum inside the hub assembly that can allow water to enter.
That won’t happen with grease. Another concern is the chance of hitting a curb with an oil filled hub, breaking its cover, and losing the bearing protecting oil right there.
It’s also been argued that oil hubs are a bad idea if your trailer sits for long periods of time. The oil will settle, through gravity, against the lower half of the bearings, leaving the upper half of the assembly prone to contamination. Again, this won’t happen with grease.
One other note about oil-filled hubs: They’re not recommended for use with solid rotor disc brakes because of the heat that is generated. If you have vented rotors, then all is well.
Both Tiedown Engineering and Kodiak Trailer make oil hubs. Tiedown offers the TurboLube system which was a 2001 Marine Aftermarket Accessories Trade Show Innovation Award winner. Tiedown recommends changing the oil every 50,000 miles or two years and to use only 70- to 90-weight oil, avoiding two-cycle.
As is the cae with grease, a milky-looking oil indicates the presence of water. Kodiak, as a matter of fact, produces a system (XL Prolube) that can convert hubs from grease to oil. One component of this system is the two-part unitized seal that slides onto the trailer spindle and locks into position while an outer part spins with the rotating hub, providing a watertight enclosure fir the bearing assembly.