Know-How: Bearing StraitsBy BoatUS Trailering Editors
Published: Fall 2012
We're not talking about the stretch between Alaska and Russia. No, this is potentially more hazardous
In a letter to BoatUS Trailering on page 6, a member does a good job explaining what it’s like to be in the Bearing Straits. You’re at the side of the road, a trailer hub is covered in grease, and all the plans for the rest of the day have come to a screeching halt.
Changing bearings is a job most of us don’t relish and while, most of the time, you can get away with not doing it for “that next weekend trip” and deal with the job later, neglected bearings can come back to haunt you. The good news is it’s a project that can easily be done in a few hours, depending on the number of axles on your trailer. But it’s also important to know what to look for before a bearing goes bad. Yes, they give you hints something isn’t right, but too many times, when you’re clipping along at 60 mph, those hints occur pretty darn fast. Prior to going on the road, take a look behind each trailer wheel.If a bearing seal is going bad, grease will be visible inside the hub. Take a look inside the fender as well because grease can be thrown there, too. This is an obvious sign that something isn’t right.
Anytime you make a stop along the way, carefully put your palm on each hub of the trailer tires. If one is warmer than the other, this means one of three things: Tire pressure is low; a brake pad is dragging; or grease isn’t able to keep the bearings running at the preferred temperature (about 120 degrees F without brakes, and no more than 200 degrees with brakes). Dust caps, both metal and the rubber outer sleeve or dust protector, can become loose, so make sure they’re properly seated and tightened.
Extreme pressure from overheated brakes
One other area to be aware of is the traditional zerk fitting, where grease is added on many hub assemblies. While generally reliable, caps with zerk fittings can lead to trailer bearing failure due to “overcharging.” The logic is, if a little grease is good, a lot is better, and that’s the start of bearing trouble. Many of the protector-style caps have spring-loaded bladders, so if the owner fills the hub and cap, maxing out the bladder, the hub overheats and the pressure has to go somewhere — usually out the rear seal or blowing the cap off. On the other hand, if the owner never changes the grease and only adds new grease from time to time, this can result in only the front bearing ever getting the new grease. The rear bearing gets all the old worn-out water-laden grease that is pushed back into the rear of the hub.
Newer versions use oil bath hubs that lubricate the bearings with a specially designed oil rather than the standard grease assembly. These are popular because one can actually look at the oil level through the hub and get a firsthand view if more oil is needed. There’s a zerk fitting on the edge to do just that. Any experienced trailer boat owner will say “you just never know when” the Bearing Straits will arrive. But that time can be delayed, if not avoided altogether, when you take care to look for a hint or two.
See video of Trailering Guy Dustin Hoover changing bearings, www.BoatUS.com/Trailerclub/magazine
Dust Cap Dramas
If the dust cap suddenly starts coming off, this, too, is a hint that something is wrong and, many times, it’s the result of the bearing assembly.
- Always check the rubber outer sleeve is properly seated on the hub because water can enter the bearing assembly during launching and retrieving. If you use a metal dust cap, be careful when using a screwdriver during removal because the cap will easily bend. Better yet, replace the cap whenever changing bearings.
- Cotter pins drag on the inside of the cap if not reinstalled properly.
- Loose bearing adjustment, causing hub to wobble and hit castle nut or cotter pin.