The bearings on boat trailer wheels are used both in and out of the water and need to be sealed to keep water out of the hubs. If water gets inside, the wheel bearing grease will not work as well and the bearings could fail. You should check the bearings on your boat trailer at least annually and replace them if you see any rust or pitting, or you feel any fine metal particles in the grease. Changing the bearings is not complicated.
Jack the wheel of the boat trailer off the ground and remove the wheel.
Insert the a flathead screwdriver between the dust cap on the end of the wheel hub and the rim of the wheel hub. Tap the end of the screwdriver with a hammer.
Rotate the hub slightly, reinsert the screwdriver and tap it again. Continue doing this around the perimeter of the dust cap until it loosens and can be removed.
Straighten the cottar key under the dust cap until it can be removed from the hole in the spindle.
Grasp the castle nut with a set of channel-lock pliers and rotate counterclockwise to loosen and remove.
Remove the washer under the castle nut. Wiggle the hub to pop the outer bearing loose. Remove that as well.
Pull the hub firmly by hand to remove it from the axle-spindle.
Position the hub firmly in a bench vice. Use a flathead screwdriver to pry the rear grease seal out of the hub, then lift out the rear bearing.
Insert a brass punch through the rear of the hub so the point of the punch is against the outer bearing cone. Tap firmly with a hammer to loosen and then knock out the bearing cone.
Turn the hub over in the vice. Insert the brass punch through the hub, putting it against the rear bearing cone. Tap firmly with a hammer to knock out the rear cone.
Place the wheel hub in a shallow pan containing a couple inches of auto parts cleaner. Use a small paint brush to clean all the old grease from the inside and outside of the hub.
Place the new rear bearing cone inside the rear of the hub and tap it into position using the brass punch and a hammer. The brass punch ensures that the cone doesn't get gouged or scratched.
Place the new outer bearing cone inside the front of the hub and tap it into position.
Insert the new inner bearing, then lay the new grease seal on the inside of the hub.
Lay a block of wood over the grease seal and strike the wood with a hammer to force the grease seal into position in the hub.
Slide the hub back onto the spindle, pushing firmly to force the grease seal onto the shoulder of the spindle.
Insert the outer bearing and the washer. Thread the castle nut back onto the spindle-end.
Tighten the castle nut using the channel-lock pliers enough that you feel some tightness in the bearings when you rotate the hub. Loosen the castle nut a 1/8 turn and reinsert the cottar pin through the spindle-end to lock the castle nut in place.
Tap the dust cap onto the hub.
Push the end of a grease gun onto the grease zirk on the dust cap. Pump grease into the hub of the wheel until you see the spring on the dust cap begin to compress.