BOAT TRAILER bearings have the unique privilege of being dunked in the water in their normal course of duty. A warm hub from traveling to the launch, suddenly gets backed in the water and the hub cools. Any air inside contracts and tends to suck water in past the seal or around the dust cap. Perfect seals and perfect dust caps won't allow this...so water always gets in. Water intrusion breaks down grease and rusts bearings, races, and axles. Salt water does it many times worse.
Bearings in good condition, fully greased, and properly adjusted, don't make any sound. If you hear anything from spinning your trailer wheel, you need to pay attention to your bearings.
First thing is getting them apart. Second thing is thoroughly cleaning the hub and bearings. Inspect the bearings. Rusted, pitted, ugly bearings are done for. Check the races inside the hub. If the races are perfectly smooth with no evidence of pitting, spalling, or corrosion, they can stay. If not, then they need to go. Bearing races(cups) and bearing rollers(cones) should be replaced together. If you find cheap crappy cheap junky bearings...replace everything. Inspect the axle. If there are worn spots where the bearings sit OR where the seal rides, then you have to decide whether the axle is a problem. Record the numbers on the bearings, seals, and races. Measure the axle diameter at the bearings and at the seal surface.
Now you have inspected all components on both sides of the trailer, go to a bearing distributor. Buy a new set of Timken bearings, Bearing Buddys, and a set of 'double-lipped' seals. Double lip seals don't let water in or grease out. This is important if running bearing buddies. Bearing buddies hold pressure on the hub cavity. If you use single lip seals the buddys will just work the grease out the back...make a mess. If you have a regular plain dust cap, or a dust cap with a grease fitting, instead of Bearing Buddys, then a single lip seal is OK. Then you can use your grease gun to pump a little grease 'through' the hub every so often, or, stuff grease into the cap and tap it on forcing grease through the hub and out the back...again messy. Bearing Buddys and double-lip seals are so much cleaner and better and everything. Either way, bearings want to be greased.
There are lots of ways to replace the races in the hub. I carefully tap them out with a tapered punch. They need to have an 'interference fit' or 'press fit'. If the races push right out, or drop right in, or if they spin in the hub, your hub is done for. Emergency repair can be accomplished by 'center punching' around the ID of the hub where the races go. This knurls or raises metal and 'grips' the race as you drive or press it in. It's a temporary fix if you gotta get the trailer on the road tomorrow morning. I've seen it last forever, but don't trust it. Races get driven in till you hear them seat. I sometimes use the old races, ground down a little, as a tool to press in the new ones. Usually a big socket will work. The best thing is to have a set of bearing drivers and/or a shop press. Don't drive in new races with a punch, that only works to get ugly ones out. Use lube in the hub and on the race to ease the installation.
Assembling bearings needs to be done with cleanliness. I use solvent first, followed with air, then carb cleaner, followed by air, then brake cleaner, followed by air. You do not want to pollute your assembly with any dirt. With everything sparkly clean, pack the bearings. Force grease by hand, or with a packer, completely into the bearings. If you have to set the bearing down, put it on a clean paper towel to keep dirt out, and cover it. Fill the sparkly-clean hub with grease leaving enough room to get the axle through. Install the rear bearing and tap the seal into place. Install the hub onto the sparkly-clean and freshly greased axle. Insert the outer bearing, wiggle the hub until the outer bearing, inner bearing, and seal are in place. Thread the nut into place. Tighten by hand.
Now the bearings need the proper adjustment. Tighten the axle nut with a wrench to seat all the components. Don't crank on it...just enough torque to 'feel' everything is seated good. Take the cotter pin, back the nut off enough to insert the cotter pin. This opens up the bearings 'just enough' to give them operating clearance. Do not back off more than 1/6 turn, or one flat of the nut. Put grease in the cap. Install the cap or Bearing Buddy and tap into place. Use a hammer that won't damage the cap. Tap it in straight. Read and follow all the instructions with the Bearing Buddys.
After all this work is done, take the trailer out for a run. Stop after the first mile or two and check the hubs for temperature. Slightly warm is OK, shouldn't be much heat there at all. Take the trailer home and check the play in the bearings. If the hub is loose on the axle with noticeable play, you need to readjust the bearings. If the hub is tight with no play, you need to readjust the bearings. There should be a nice, smooth rolling, silent, controlled action with only a hint of play, no tightness or tight spots.
Keeping the hubs in this condition is easy with the Bearing Buddys. Have a grease gun loaded with the same grease you used to assemble the bearings. Don't mix greases. Use the gun to pre-load the hubs until the spring is compressed in the bearing buddy. Don't add any more or you will push the seal out the back of the hub. The spring will keep the hubs pressurized even when you back into the water. No water can get in if there is pressure inside. If you forget to add grease and the spring pressure gradually decreases, the Buddys will have no advantage over regular dust caps. Keeping them filled and the spring compressed means your expensive bearing job could last as long as you own your trailer. Make this part of your pre-trip inspection...every time.
If you are traveling to buy a boat, or anytime you have to tow an unknown trailer, take basic tools for servicing bearings. More than once I have picked up trailers with ratty old rusty bearings. Disassembling, cleaning, and packing rusty/shot bearings in a Walmart parking lot can make the difference between getting home and sitting on the side of the highway with the hub welded to the axle, or bearing fragments all over the road. If you're towing a boat home that you just bought...likely you haven't performed all the legal paperwork just yet. What a target you are sitting on the side of the road with a smoking hub. Ticket(s) and towing...etc.
OK so, that's about all I've learned about trailer bearings, most of it the hard way.
