Over time the bearings in the hubs of a bicycle wheel may come out of adjustment causing the wheel to wobble from side to side (this can also be the result of the wheel being out of true; a sure sign of loose bearings is that the rim can be moved laterally in the fork by hand). Additionally, road dirt and moisture infiltrate the bearings, causing rough operation and premature wear. Even if these issues do not arise, the bearings’ lubrication will eventually need to be replaced in order to maintain the life and health of the hubs. These problems can be addressed by overhauling the hubs. The basic techniques are similar to maintaining any other ball bearing assemblies, whether the headset or bottom bracket on the bike, or on complete different applications.
On some recent model mountain bikes, there has been a rash of rear hubs getting significant play after only a few rides; this may be due to bad cones or lock nuts. The drive side lock nut should be your number one suspect in this case if the bike is new.
Parts of the hub
From the inside out:
- Bearing cup
- Bearing cone
- Dust cover
- Lock washer
- Lock nut
- Quick release skewer
Main body of hub, holds the axle assembly and is the connection point for the spokes.
Is pressed into the shell.
Forms the outside bearing races, fits onto axle, usually adjustable.
There are three major types of bearings in use on bicycle hubs:
Cup and Cone types
- Loose ball bearings are placed individually in the bearing race
- Caged bearings are simply loose ball bearings held in a framework, which simplifies their insertion in the hub. They differ from sealed, or cartridge, bearings in that the bearings are visible in a simple cage made of a circular piece of sheet metal with holes punched for the bearings, and the bearings can be inserted and replaced into the cage with simple hand tools, or even just with the fingers. Cup and cone bearing hubs also usually have some form of sealing but it is separate to the bearings.
- Cartridge bearings are assembled and sealed in a permanently pressed housing which renders them inaccessible. Cartridge bearings which are sealed have the advantage of being highly effective at preventing dust and moisture from entering bearing housing and usually need no adjustment. They will generally last many years without service. If they do fail, they are simply replaced. Some hubs cannot be disassembled when the cartridge bearings are worn or fail; the more expensive ones can sometimes be serviced by the manufacturer…
Cleaning and repacking a traditional cone and cup front hub
- Place the wheel flat. Have something under the hub to catch loose bearings (unless you know for certain that they aren’t loose). Usually, it does not matter which side of the wheel is up, however a few nonstandard axles have the cone on one side cast as an integral non-removable part of the axle and therefore the other cone must be on the top side for removal. This will be obvious to inspection.
- Using a box or cone wrench, unscrew the lock nut from the cone. It will be necessary to hold the cone from rotating while doing this; this will usually require a cone wrench, as the width of a normal open or adjustable wrench head is too great to fit on a normal cone.
- Remove lock washer and any other hardware.
- Unscrew bearing cone
- Pry out circular dust cover situated above bearings (this may also be done after axle is removed, as is necessary on the bottom side of the wheel)
- Separate wheel and axle
At this point, depending on how the grease is distributed on the parts, the ball bearings may well stick to the axle, or drop out of the hub or into the axle hole through the hub, or remain in the cup. If the bearings are in a cage, they will generally remain in place unless the cage has been excessively worn.
It is advisable to leave the other cone and locknut assembly undisturbed in its position on the axle, as this will allow you to maintain the original side to side alignment of the axle assembly in the hub as much as possible. (Of course, this is mandatory where this assembly is not removable). It can be cleaned and greased in this condition. (If the cone is damaged, then it will need to be disassembled and replaced).
- Clean and inspect the bearings. Be prepared to replace any that are cracked or pitted. Most mechanics simply replace all loose bearings with new ones, as the cost is minimal compared to the labor involved in cleaning and examining old ones, and if the hub is reassembled with a bad or dirty ball it will rapidly wear. Similarly, caged bearings are usually replaced as a set, cage and all; in most cases, however, it is advantageous to replace caged bearings with loose bearings of the same size, as this results in a greater number of bearings in the hub, providing greater area and therefore greater resistance to wear, at the expense of only slightly more difficulty in keeping track of the bearings during assembly.
- Clean and inspect bearing cones. There should be no scratches or rough spots at all in the smooth track caused by the rolling bearings. A damaged cone can usually be replaced.
- Clean and inspect cups.
- The cup is factory pressed into the hub shell or sometimes cast as part of the shell, and is not generally user removable. Once again, the track of the rolling bearings should be completely free of scratches or rough spots. If the cup is damaged, sometimes a shop with a press can replace it.
- Grease bearing cups
- Re-insert bearings, which should be held in place by the grease
- Put another layer of grease on top of the bearings
- Re-insert dust covers
- Re-assemble by reinserting axle from underside, and replacing the cone, washer(s) and lock nut on top.
- Adjust as necessary. For ball bearings the adjustment is somewhat particular; there should be no excessive drag from over tightening, but also no excessive play from looseness. Although the proper adjustment is pretty obvious by “feel”, tightening the locknut on the cone usually disturbs the adjustment enough to throw it off; therefore a bit of experience helps to estimate to what tightness the bearings should be adjusted, before tightening the locknut to produce the correct result afterwards. In practice, usually three wrenches are needed; one on the locknut, a cone wrench on the cone, and a third wrench on the locknut and cone assembly on the underside of the wheel, presumably firmly gripping the axle. This provides the ability to minutely tighten or loosen the top cone and locknut independently until the perfect tightness is achieved.
Maintaining a cartridge bearing hub
There are many different designs so this is just an overview of the basic principles that can be used to service most cartridge bearing hubs.
Clean and lubricate bearings
If you ride in wet conditions you may be able to extend the life of the bearings by periodically cleaning and lubricating them. In most circumstances this is not required and the bearing will have an acceptable life with no maintenance.
The idea is to remove one of the seals from the bearing so it can be cleaned and fresh grease applied.
- Typically the end caps block access to the seal so need to be removed. The method of attachment varies from hub to hub. Some just press on and can be pulled off by hand, others screw onto the axle and have flats for removal with a spanner or are held on by set screws. The end caps may also be part of the axle itself and the axle is removed by inserting an allen key into each end of the axle and unscrewing.
- Now there is access to the seal it is removed. This can be done by prying it out with a razor blade or small flat head screwdriver.
- Clean the bearing using degreaser and or rag.
- Apply fresh grease, a grease gun makes the job easier.
- Push the seal back into place and replace the end caps.
Replacement bearings can be sourced from good bike shop or from any bearing supplier. Typically bearings are identified from the numbers on the side of the bearing, take the old bearings with you to make sure you get the correct replacements.
Removing old bearings.
- Remove end caps. Some just press on and can be pulled off by hand, others screw onto the axle and have flats for removal with a spanner or are held on by set screws. The end caps may also be part of the axle itself and the axle is removed by inserting an allen key into each end of the axle and unscrewing.
- Remove axle. Use a rubber mallet to hammer the axle out of the hub. The step on the axle will push one of the bearings out of the hub shell. Remove the bearing from the axle and use the axle to remove the other bearing from the hub shell.
- Some hubs do not use an axle with steps for the bearings to push against. These typically have a spacer instead. To remove the bearings push the spacer to the side and use a rubber mallet and a large flat head screwdriver to push the bearings out of the hub.
- Clean and inspect the hub shell and axle.
Installing new bearings.
Cartridge bearings are not good at absorbing side loads. When being pressed into the hub the force needs to be pushing on the outer metal ring to avoid damaging the bearing. A suitable sized socket can be used to do this.
- Lightly grease hub shell and axle where bearing will sit.
- Press a bearing into one side of the hub shell. Use a rubber mallet and socket trying to keep the bearings as straight as possible.
- Insert the axle or spacer.
- Press the second bearing into the hub. The bearing should be pushed in far enough that there are no side loads on the bearing. With good quality hubs you should just be able to push it in all the way and have everything line up. Cheaper hubs may require care to avoid putting side loads on the bearing. If the hub has a spacer to help keep it lined up you can insert the axle part way into the underside of the hub.
- Put the end caps back on.