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Keeping Trailer Wheel Bearings Properly Maintained

John Tiger, Jr.
January 2007

It's a subject as old as trailering itself, but keeping wheel bearings properly greased and maintained is a ritual many still forget to perform. The evidence of that is clear. It's still easy to catch a very familiar sight on the side of any highway in America on a hot summer day; a family sitting dejectedly on the grassy roadside, perhaps eating a picnic lunch, while Dad goes off to find a marine service dealer who can replace the trailer's damaged wheel bearings. While servicing wheel bearings isn't glamorous or sexy, it sure can save a lot of lost time and certainly prevents the loss of valuable vacation time — something no one can afford to lose.

Today's wheel bearing assemblies are no different than those of twenty, thirty or even fifty years ago. They still use grease as a lubricant and coolant, they still employ caged rollers that roll on a pressed-in race, and they still use a rubber-lipped seal to keep grease in and water out. What's changed is the grease used to lube them; today's synthetic greases, if used, can offer longer bearing life and a more forgiving environment against roller failure. In addition, there are more methods of protecting and greasing the bearings without actually changing the grease than ever before. While "Bearing Buddy" protectors have been available for many years now, they've since been improved, and have met many forms of competition. In addition, new forms of lubrication have been introduced in recent years; oil bath systems offered by several manufacturers have become more popular.

While greasing the bearings through an outside fitting can keep the water and potential corrosion at bay for a while, the most effective way to ensure that the bearings are full of fresh lubricant is to change the grease on a regular schedule, just like your Dad did before you. The only advantages that protectors like Bearing Buddies gives to today's trailer boaters are reduced grease change intervals and the ability to "top off" the grease between changes. Regardless, the grease should be changed at least once per season (more often if you trailer long distances or trailer frequently).


If you've never changed wheel bearing grease before, be prepared for a messy afternoon. Time-wise, that's about all it will take you, even for first-timers; it's an easy job. Tools needed are few and simple. You'll need pliers (side-cutting pliers work well when removing stubborn cotter pins), a lug wrench to fit the lug nuts on your trailer, a jack, jack stand, a hammer, large flat-bladed screwdriver, and a short (six inch) length of scrap 2x4. Of course, a grease gun with zerk end fitting will be needed if your wheels have bearing protectors installed (such as part number 1980S, 1781S, or 2047). A large pair of pliers (water-pump pliers or Channel Locks as they're sometimes called) may be needed if the large nut holding the hub on has been tightened too much.

If they don't have them now, this is the time to fit your wheel hubs with bearing protectors. Available from just about any trailer dealer, hitch installer or auto parts store, bearing protectors have become commonplace — RedTrailers.Com stocks the most popular sizes. Most common among boat trailers are the 1.781" and 1.980" inner-diameter sizes, but if you're in doubt, take your dust cap along with you to match up the inner diameter (the part that fits into the bore of the wheel hub). A pair of bearing protector covers will only add a few bucks to the tab, and protect your wheels from any excess grease that may escape the hubs at highway speeds.

While you're shopping, pick up a tub of wheel bearing grease. For those on a budget, regular mineral-based grease will work fine, but for the ultimate protection at slightly higher cost, synthetic grease will last longer in the hub and tolerate water ingestion better. Lastly, though it's not needed, a bearing packer will make filling the bearings with grease a much easier job — and much easier to clean up. Without one, you'll have to pack the bearings by hand. This simple tool allows you to capture a wheel bearing between its two plastic discs and pack it with grease using a grease gun. That's a lot neater and quicker than filling your palm with a blob of grease and wiping it into the bearing cage. Bearing packers can be purchased at any auto parts store, Sears, or big-box home centers for less than $20. It's a good investment, and besides — what fun would the job be if you didn't get to buy a new tool for your collection?


You'll have to jack up the trailer's axle, one side at a time, to service the wheel bearings. A floor jack is best but if you don't have one, the bottle jack from your truck will do fine. A jack stand is also needed to secure the trailer in the raised position and ensure that it won't come crashing down on you in the middle of the job.

Before raising the trailer, loosen the lug nuts. Jack the trailer up until the wheel can spin freely. Remove the lug nuts and the wheel, exposing the hub assembly. Check the back side of the hub, wheel and tire for grease spatters. If you see grease, the rear seal has failed and will need replacement.

You can now remove the hub. The dust cap or bearing protector must come off first. A dust cap has a small lip that can be pried off by carefully using a flat bladed screwdriver; lightly tap the screwdriver blade under the lip with the hammer, rotating the hub as you pry off the cap. Bearing protectors have no lip to pry under, so you'll have to (again, carefully) tap the outer diameter of the protector as you rotate the hub. If you use a plastic mallet instead of a hammer, you won't mar or dent the protector.

After you remove the protector/cap, rotate the hub slowly as you listen closely for irregular noises. You should hear nothing as the hub spins; if you hear grinding, scratching or rattling noises, of if the hub moves excessively on the axle shaft, you probably have bearing problems. A cotter pin keeps the castle nut from loosening; bend it out straight and remove it with pliers. If it's been bent too many times, replace it with a new one. Remove the castle nut and washer, then remove the outer bearing. Keep plenty of rags handy to catch loose globs of grease that may fall out as you remove the hub assembly from the axle.


A parts washer makes this step much easier, but if you don't have one, you can improvise with an old wash pan and a half-gallon of gasoline or parts cleaning fluid. Remove as much loose grease as possible from the outer bearing, hub, and inner bearing. If the rear seal is damaged, or if you detect problems with the inner bearing, pry out the seal with the flat screwdriver and discard it. Remove the inner bearing. Often, if the grease is still in decent condition and you can inspect the inner bearing by feel and with a flashlight, you might be able to get away with cleaning it and regreasing it without removing it (and the seal). You can leave it in place along with the rear seal; just be sure to wash out all the old grease and dirt using the solvent. However, I'd recommend replacing the seal and cleaning/regreasing the inner bearing every time.

Wash the parts as thoroughly as possible in the solvent (don't forget the nut, washer and cotter pin, as well as the dust cap/bearing protector). If possible, blow-dry them with compressed air to remove all remnants of old grease, dirt and washing fluid. NOTE: BE CAREFUL and DO NOT spin the bearings at high speed with compressed air! Spinning a bearing at high RPM with no lubricant can cause it to literally EXPLODE in your hand, causing severe injury. DON'T DO IT!

After cleaning and drying, inspect all the parts closely. If the roller bearings appear pitted, scored, galled or rusted, you must replace them. Take them to a trailer dealer for an expert opinion, if you're in doubt; replacing them with new ones now is far easier than when you're stuck on the roadside. If you replace them, replace the bearing races as well; these are press-fitted into the hub. They can be removed with a hammer and screwdriver, but have the dealer do it while you're there buying the new bearings; it's easier for him to do it with a shop press, and you won't risk damaging the hub with the hammer and screwdriver.


Packing the bearings with grease goes quickly with the bearing packer. Place the bearing on the bottom cup, screw the top cup down snugly over the bearing, attach a grease gun, and pump grease into the bearing until it just begins to flow out the sides of the rollers. If you elect to do it by hand, place a gumball-sized dollop of grease in the middle of your palm, and taking the bearing in your other hand, firmly wipe the edge of the bearing through the grease. Do this repeatedly until grease begins to appear on the other side of the bearing. Rotate the bearing as you go, ensuring that it's filled completely around. This is why the bearing packer is highly recommended; it ensures a fully-greased bearing, makes the job easier and cleaner, and the cost is low compared to the value the tool gives. Set both bearings aside on a clean dry cloth.

If you removed the inner bearing and seal, now is the time to re-install them. Check one more time to ensure that the inner bore of the hub is completely clean and dry. Place the greased inner bearing into the hub, seating it in the race securely (the grease will hold it there). Now, replace the rear seal. Clean the hub bore where it seats with solvent, making sure there's no grease, old sealant or dirt there. Select a short socket that matches the seal's outer diameter to use when pressing it into the hub bore. Coat the outer edge of the seal with liquid sealant, and gently tap it into the hub with a rubber mallet, using the socket as an installing tool. Seat the seal flush with the end of the hub bore; don't tap it any deeper.

Clean the axle shaft and inspect it for damage. If there's deep scoring, pitting or rust where the bearings ride, it may be time for a new axle stub. This can be an involved job, best left to a good trailer mechanic. If the area where the seal rides is scored or pitted, you can easily solve the grease leakage problem this causes by fitting the axle with a Spindle Seal, which is a stainless steel seal and O-ring kit that fits over the inside of the axle stub, forming a smooth sealing surface for the hub seal to ride on. Spindle Seals are manufactured by Bearing Buddy, and are available at most marine and trailer dealers.

Coating the axle shaft with grease before installing the hub will help ensure that enough grease is in the hub before it turns its first revolution. Put a healthy dollop of grease inside the hub, then slide it on the axle shaft. Next, install the outer bearing, making sure it's seated in its race. The outer washer fits in next, then the castle nut. Tighten the nut down as you spin the hub, ensuring that you don't tighten it so far that it slows the hub or stops it from turning. Grasp the hub's outer diameter and try to move it back and forth; if you can, the nut is not tight enough. Tighten the nut to the point that it slows the hub from turning, then back off a quarter turn and check for side-to-side movement again. If you try this step a few times, you'll get a good feel for how tight the nut should be. It can be tricky; too tight and the bearings will wear prematurely, too loose and the wheel will wobble. After you've found that "sweet spot," turn the nut slightly to expose the cotter pin hole and insert the cotter pin; bend the ends out and around the nut. Make sure the ends don't get in the way when you install the dust cap or bearing protector.


Clean the hub bore using solvent and a clean rag, then using the short length of 2x4 to avoid damaging the bearing protector, tap the protector into the hub with a hammer. Make sure it seats fully; you'll notice a different tone in the sound of the hammer blows when it does. Using the grease gun, pump grease into the bearing protector as you spin the hub to distribute the grease inside. Here's another tricky part; don't over fill the hub, or you'll blow grease right out the back of the rear seal. Some bearing protectors have an indicator that tells you when the hub is full. Without that indicator, watch the spring inside the protector carefully as you fill; when it fully compresses, stop pumping grease. Wipe any excess away, re-install the wheel and tire, and you're done — with that wheel. Now you can repeat the process for the other wheels on your trailer.


Costs and time spent are minimal for this job. Grease is cheap and readily available. A grease gun is a good investment, and should be taken with you on road trips in case of bearing failure or just a simple top-off. Grease guns are available for less than $20 in most home centers and hardware outlets. As mentioned, the bearing packer is a worthwhile tool to own for less than $20. Time involved is approximately one hour per wheel, so for a dual-axle trailer, expect to spend the afternoon with greasy hands. In all, this is a job every trailer towing enthusiast should be familiar with. If you end up needing new bearings and seals, these cost less than $25 for two sets (enough to do a single axle trailer). Just be sure to take the old ones with you to the auto parts store so the counter man can match them to a new set.

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