In a related question, Tools and supplies for roadside trailer bearing repair, @Pᴀᴜʟsᴛᴇʀ2 said:

Something to think about is to worry about preventive maintenance more than worrying about having a breakdown on the road. If I were you, I'd put zerk caps on the hubs so you can push new grease into the hubs very easily.

The number one killer of the bearings on these is because of water ingress. If you check the seals and keep it greased regularly, it becomes a non-issue and breakdowns due to the hubs will become non-existent. One of the issues is, if you suffer a hub breakdown, you'll do more damage before you notice it than what you can repair on the side of the road (most likely).

Wheel: 5.70-8 4-bolt

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What is involved in installing zerk caps on boat trailer bearings, and what tools and supplies are required?

I'm going in green; I don't have any experience with bearings/grease/trailer mechanics.

1 Answer 1


If you have the tools, you can just install the zerks into the old caps by drilling small holes (holes just a bit smaller than the zerk's threads) and force threading the zerk into the caps. The zerk will create its own thread by deforming the hole in the cap. Then, just grease it from the outside as needed. Once the zerk is installed, it will take a bit of grease to fill the void, but the bearings and all will be completely coated in grease which will prevent most water ingress due to submersion.

To do this job, all you need is a drill and a bit the right size, along with the zerk, of course. You don't want to drill the holes while the caps are on the trailer, so you'd need a pair of channel lock pliers to pull the cap off. Take the caps off to do the job because you don't want to get metal into where your bearings are at. Don't over tighten the zerks, because you'll pull the zerk right out of the cap.

  • Thanks! What kind of grease do you recommend? For example, I have some Synthetic Grease. But I'm not sure if that's the right stuff or not.
    – User1974
    Jul 16, 2023 at 20:41
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    If you are using zerks, the intent is to use a grease gun. It's the only way you can get the grease into the cap/bearings without taking the cap off. If you take the cap off, you defeat the purpose. Something like this. Once you have the grease gun, you can put a tube of whatever high pressure grease you want to use. This and this will work Jul 16, 2023 at 20:49
  • That helps. Thanks. Is there any concern that the zerk will cause wheel balance issues? Should I position the bearing cap so that the zerk is opposite of the tire valve, to balance things out?
    – User1974
    Jul 16, 2023 at 20:57
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    No. Just center the zerk in the cap. Even if you are off by a little bit, the inertial forces are soooooo small, it wouldn't make a difference. The zerk is at the center of the cap and poses absolutely no risk of making the wheel out of balance. If you aren't feeling like this is a job for you, I notices Princess Auto sells the caps with the zerks already in them. Just get one the same size as the cap which is on your boat. A little more expensive, but maybe worth the hassle. Jul 16, 2023 at 21:01

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