Replacing a boat trailer bearing.

How to change trailer wheel bearings

We won’t be going into issues like trailer-shaft condition, wheel hub problems, or the dismantling of various trailer brake-setups. All we want to do is access and replace the bearings on a standard single-axle boat trailer.

To replace the wheel bearings on a boat trailer, start by safely setting your jack under the side of the trailer. Next, jack it so that the wheel sits just off the ground. You don’t need to get under the trailer so don’t expose yourself to unnecessary risk.

There are two ways to protect newly installed trailer bearings. The first is to use a standard wheel hub metal cover (cheap and a little nasty); the second is to use a Bearing Buddy or similar system.

A Bearing Buddy is a cylindrical housing with an internal spring-loaded washer that pressurises the grease from the outside, ensuring that water is less likely to enter the bearing area. This is by far the best method if you want your bearings to last.

It’s not a technical job but it’s worth the effort. Ask yourself: how many boat trailers have you seen stranded on the side of the road with a buggered bearing? Yeah, that many, eh?


Replacing a trailer bearing

This tyre is left on the hub. All you do is straighten the split-pin and remove both the pin and the nut to remove the tyre and hub. Leaving the tyre on the hub can make the job easier and quicker. You can also see here that the grease is a light grey colour, a good indication that water is getting in. The bearings are not as bad as first thought, but for around $30 to $40 a wheel it’ll pay to replace them.

T he next step is to remove the old bearings. Be careful if you plan to keep them as spares because you never know what can happen when metal mixes with saltwater. If you don’t want to keep them, get in there and just knock ’em out. The main sections of the bearing case will come out without too much difficulty so just ease them out with a long screwdriver.

You can see here that the old collars have also been removed. They can be tricky, so use a screwdriver if it’s an emergency roadside removal. Otherwise, a copper dolly (a copper-ended type chisel) will do. You could also use your screwdriver but take extra care not to damage the inside of the wheel hub. If you’re confident that the original bearings can be reinstalled, remove all the old grease and check for wear and tear. Also look out for heat damage, indicated by a bluish tinge in the metal.

Clean all the old grease off the axle and check for further wear or heat damage. This is quite common but it’s often overlooked. The best way to get the old grease off without you wearing it is to use cheap plastic gloves. You might go through a few pairs but what the hell, they’re cheap as chips. 

Now for the messy bit. Using a newspaper, scrape out the old grease and gunk from inside the wheel hub. Then finish the job by pulling an old towel through the assembly. Once the old grease is out and the hub clean, check for further wear or heat damage inside.

 Pre-grease the hubs and new collars so they’re ready to be hammered into the hub. Remember to put the collar in the right way. The new bearings must sit inside the collar, after the collar is in position (cone facing out). Hammer the new collar in evenly using your copper dolly, and check that you’ve tapped the collar in all the way. One trick is to run your finger along the ridge inside the hub, checking for unevenness. You can also tap them in with a short length of PVC of the same diameter as the collar.

Now for the important part — packing your bearings with grease! It’s a lot easier than you’d think, so get a good dollop of grease in your hands and slap or force it through the gap between the inside and outside of the bearing. It should ooze out the top and into the bearing. Keep doing this until you’re confident that the bearing is chocked full of grease.

Now all you need to do is put the new metal ring and rubber seal on the inside, then put the wheel back on the trailer. Tighten up the nut so everything is pushed in and seated nicely, then back the nut off a touch. This should be enough to allow the wheel to spin, but not so that it wobbles.

And that’s it, you’re done!

Originally published in TrailerBoat #257, June 2010.