Thursday, March 25, 2021

Bearing Replacement


If it turns on a shaft, it probably has bearings. Bearings wear out with use and are considered a “consumable” item, they are designed to be replaced on equipment that is intended to be used for any length of time. The cheap, imported gear (tools, rolling stock, and machinery) is often not designed for long life. It's often cheaper to throw away a modern tool than it is to repair it- this is by design. “Planned obsolescence” was a marketing strategy that gained a wide following in the 1970s, that's the idea that in order to get repeat sales you need to make everything so poorly that it will fail shortly after the warranty expires. This is why I shop flea markets and estate sales for older tools and equipment, I have a better chance of finding something that will be usable for many more years rather than having to throw it out. I have power tools and kitchen appliances older than most of our readers that are still working, try finding anything in a store today that you'll be able to pass down to your kids or grandkids.

Bearings are simple, I covered the basic types last week, and most of them are replaceable. The work of replacing them can be dirty, greasy, and a pain in the neck but is generally worth the effort. Being able to do some of your own basic repairs makes you a little bit more independent and opens up opportunities to rehabilitate things that others have no further use for. Fixing up a trailer, wagon, bicycle, or vehicle might come in handy if our normal system of supply crashes. We invented the wheel to make life simpler, it would suck to lose them.

Most bearings are assembled in a hub that connects the wheels to the axle/shaft. I'll use a diagram of a common trailer hub/axle to explain the parts and procedures, bicycles and vehicles are very similar with minor differences due to the load they carry.

Courtesy of

This is a boat trailer hub, the dust cover is water-tight and designed for ease of adding grease to push out any water that may have gotten into the hub. Other trailers and most vehicles use a simple metal cup-shaped dust cover (this is the original “hub cap”). Dust covers are most commonly pressed or hammered onto the hub, there are no threads, so removing them takes a small hammer and a pry bar. Gently tapping on the pry bar to force it into the joint where the cap meets the hub will give you enough of a gap to pry the cap off. Work around the cap as you tap and pry, don't try to do it all from one spot or you'll damage the cap.

Once you get the cap off, you should see a mess of grease and metal parts. If you don't see any grease, you either have sealed bearings or it was assembled wrong. Grease is cheaper than bearings, so I was taught to always pack grease in until you can't see the bearings. This keeps water and air away from the metal to prevent rust, but also makes it a mess to work on. Current training is to always wear vinyl gloves when working with oil and grease (latex won't last very long, it dissolves), but I normally just clean my hands rather than wear plastic gloves. Wipe away as much of the grease as you can so you can see what you're working with.

Once you can see the retaining nut, give the hub a good shake front-to-rear and side-to-side. Any wobble you can feel is too much wear on the bearings. The retaining nut is locked in place by either a cotter key (if the nut is “castellated” and has notches cut in one end) or a locking collar underneath it (if it is a standard nut).

Cotter keys are rarely reusable, but you might get lucky, I've seen a lot of nails and bits of wire used when replacement cotter keys aren't available. Cotter keys are a piece of soft steel or aluminum wire that has been bent back on itself. Inserted through a hole in the axle, the “legs” of the hey are then spread apart to keep it from falling out. To remove it, use small pliers to straighten the legs back out and pull it back through the hole in the hub, twisting as you pull.

Locking collars look like washers with tabs around the edge. Once the retaining nut is in the proper position, one or more of those tabs is bent up against the flats of the nut to keep it from turning. To remove the nut you'll have to find the tabs and use a chisel or pry bar to push them back down.

Removing the retaining nut should be simple, they're not forced on with a lot of torque and they come off easily. Once you've done that the hub will come off of the axle. The outer bearing is behind a thick washer and will drop out without effort, but the inner bearing should have a dust/oil seal behind it and those can be more difficult to pop off. Tapping around the back of the hub with a hammer, sometimes with a bit of force, will pop the inner seal off of its shoulder on the axle and let you remove the hub.

Now that you have the hub off, it's time to decide what needs to be done to it. If there wasn't much free play in the hub when you tried to shake it, you can get by with cleaning and re-greasing the bearings. If the bearings or races (cups in the picture above) are discolored from heat (usually blue tints, but any color other than shiny metal), are rusted, or are obviously damaged they'll need to be replaced. Remove as much grease as you can using rags and/or solvents if they're available. A stiff brush and a bucket of diesel fuel is a quick way to remove a lot of old grease, but be safe while doing so,

Outer bearing will fall out easily. There are bearing pullers designed to gently extract the inner bearings and both races, but a hammer and long punch will do in a pinch. The hub has precision-bored holes for the races to sit in, but there will be notches in the bottom of each hole. The bearing extractors have “fingers” that catch the lip of the races at these notches and pull them out. Using a hammer and punch from the back side, you can gently tap on that lip exposed at the notches, alternating between the notches with each tap. The goal is to slide the races out of the holes as evenly as possible without getting it cocked to one side.

Modern bearings will have part numbers laser-etched into one of the flat surfaces, any decent parts store can find you replacement parts if you have the numbers. If there are no visible numbers, check parts catalogs and the manufacturers information to find them, otherwise you're going to need a good set of calipers to carefully measure inner and outer diameters of the bearings and races. Taking those measurements to a GOOD parts store will get you replacements, but you'll have to find someone who knows their job. If you plan on having this piece of equipment around for years, having extra bearings on hand at home is cheap insurance.

OK, the old ones are out and you have the new ones in hand. Reassembly is pretty straightforward, but you need to grease the bearings before installing them. The old-school method is to place a large blob of fresh grease in the palm of one hand and swipe the outer edge of the bearings through the blob to force grease up into the bearing. Dig that edge into the grease, pushing down against your palm to make sure the grease is going up into the bearing. Modern shops have toys that “pack” the bearings without the mess.

Races are a “press-fit”, so they need to be forced into the hub. Having a hydraulic press makes life easier and ensures that the races go in straight, but you can get the job done with a hammer and some properly-sized pieces of steel. I look for large sockets that are the same size as the outer diameter of the races and use them to guide the races into the hub. Slow and gentle taps on the sockets while checking alignment will get them seated. I have seen people use sockets on each race with a threaded rod run through the centers. Tightening nuts on the threaded rod will gently force the races into position.

Once both races are in, place the packed inner bearing into its race and install the oil/dust seal. This is another press-fit, but seals are very thin metal so you have to be extra careful to keep them straight. At this point, I normally add extra grease to the cavity in the hub between the bearings. Filling that cavity ensures that the grease in the bearings stays there and doesn't flow out when the bearings warm up.

Place the hub on the axle and push it on until the oil seal pops up onto its shoulder. Next you install the outer bearing and washer, followed by the retaining nut.

Tighten the retaining nut until it touches the washer. Sometimes you'll be able to find a torque setting for the retaining nut, but on most trailers you want it snug enough to eliminate wobble but not so tight that you're putting excess pressure on the bearings. If you have a cotter key set-up, tighten the nut until it touches the washer, then turn it until you have the holes lined up for the cotter key. Install the cotter key and bend the legs to keep it from moving. Locking tabs are about the same, get the nut tight enough to hold everything in position and find a tab that you can bend up to keep the nut from turning.

Pack some extra grease in around the retaining nut to protect it and place the dust cap into place. Using a rubber hammer and tapping on the dust cap as you spin the hub will get it seated. Put the tire back on and that job is done.

There you go, you're ready to get rolling again. Doing this yourself saves a lot of money and gives you confidence in your equipment. Taking it to a shop is less messy, but the rates they charge is getting ridiculous. Spending a couple of hours in the garage learning how to do it yourself will also give you the knowledge you need if you ever have to do it away from home. I've done a few trailers on the side of the road and more than a few pieces of agricultural equipment literally out in a field.

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