Bicycle Repair Cleaning and repacking a hub

 

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Over time the wheel hubs of a bicycle 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; close examination of what happens at the axle when the rim is wiggled from side to side will differentiate between the two cases). Additionally, road dirt and miosture 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:

• Shell
• Bearing cup
• Bearings
• Bearing cone
• Dust cover
• Lock washer
• Lock nut
• Axle
• Quick release skewer

Shell

Holds the axle assembly and is the connection point for the spokes.

Bearing Cup

Is pressed into the shell.

Bearing Cone

Forms the inside of the bearing race

Bearings

There are three major types of bearings in use on bicycle hubs:

Cone and Cup types

• Free bearings are placed individually in the bearing race
• Caged bearings are 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 beargins, and the bearings can be inserted and replaced into the cage with simple hand tools, or even just with the fingers.

Cartridge type

• Cartridge bearings are assembled and sealed in a permanently assembled cartridge, which renders them inaccessible. Cartridge bearings have the advantage of being highly resistant to infiltration by dust and moisture, and usually needing 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 sometime be serviced by the manufacturer.

Cleaning and repacking a hub

For 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 undistrubed 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 generally 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
• 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 overtightening, 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.

 

 

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