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This article gathers information common to many models of Shimano internal-gear hubs. Information about specific models is in the articles about
Pages about the 4- and 11-speed hubs are in process...
There are also articles on this site more generally about
These hubs have a overlocknut spacing ranging of 127 to 135 mm, as sold: see Shimano's overlocknut spacing chart. Additional spacers can take hubs out to 135 mm. If there is no brake installed at the hub, the overlocknut spacing can be smaller, down to about 126 mm, using thinner spacer washers. The Shimano "Center Lock" splined fitting is intended for attachment of the Shimano Rollerbrake; aftermarket adapters are available to allow use of disk brakes of other brands.
Shimano sells shifters for these hubs only for flat handlebars, but aftermarket shifters are available to fit drop bars.
A special and important vulnerability of the Shimano 7- and 8-speed hubs is with the large outer bearing cup at the right side. Shimano has improved its dustcaps over the years, but still, this bearing race is easily contaminated with water, and if it becomes pitted, the hub shell must usually be replaced. Then it is usually most practical to replace the entire wheel. That reminds me of a saying: "for the want of a nail the shoe was lost; for want of a shoe, the horse was lost; for want of a horse, the rider was lost; for want of a rider, the message was lost; for want of a message, the battle was lost, for want of a battle, the war was lost." Whew.
(The right-side bearing cup of some 8-speed hubs is, however, indicated as a replaceable part. If you succeed in rplacing one, please let us know how!)
Messengers on horseback are, very 1700s. You benefit from digital communication -- you are enjoying it right now -- but we still have to do battle with wet weather. Oil lubrication is highly recommended to keep water out of the mechanism. Coaster-brake hubs cannot be oil lubricated; they must be lubricated with a special high-temperature grease.
These sprockets are readily available in a range of sizes from 13-24 teeth. By changing the sprocket, you can raise or lower all of the gears at once.
The sprocket is held in position by a spring circlip (snap ring). The circlip can be pried off with a thin flat-blade screwdriver, and the sprocket can then be lifted off.
Most sprockets made for this system are "dished" so you can adjust the chainline by flipping the sprocket over.
The circlip snaps on, also most easily by levering it into position with a flat-blade screwdriver.
After re-installing the sprocket, it is a good idea to seat the circlip by going around it and tapping with a hammer and punch. This is especially important on coaster brakes, because the brake will become inoperative if the sprocket slips off.
Both of these systems provide quite a good rear brake, which works as well in rain and snow as it does on a sunny spring afternoon.
The Rollerbrake uses a proprietary splined attachment, but aftermarket adapters are available to fit a standard 6-bolt disk brake rotor.
There is also a front roller brake available, but, in my opinion, a conventional cantilever brake is better for the front. I would not particularly recommend the Nexus front brake. [Shimano has introduced an improved model with better heat dissipation since Sheldon gave that advice; still, except on a bicycle with a suspension front fork, there is an issue with fork-blade loading, as with any front hub brake. -- John Allen]
The cassette joint parts are different for the 7, 8 and 11-speed hubs. Seethis documentdescribing differences.
Cassette joint parts are different for the 7, 8 and 11-speed hubs, but adjustment is similar.
The adjustment is made with the shifter in 4th gear for the 7- and 8-speed hubs, 6th gear for the 11-speed hub. On the right side of the hub, just outboard of the sprocket, there is a "cassette joint pulley" which the cable turns as the gears are changed. Next to this is the "cassette joint bracket" which is stationary. Both the pulley and the bracket have index marks, and gear adjustment is correct when the marks on the two parts align with the shifter in 4th gear (6th gear on the 11-speed).
There are two sets of these marks, one on top, the other on the bottom. This lets you see one set of marks whether the bike is right-side up or upside down.
This procedure is the same for the Nexus 4-, 7- and 8-speed hubs, using 4th gear as the reference in all cases. In the case of the 8-speed, however, the marks you need to line up are yellow, not red.
Internal gear hubs always require some system for preventing the axle from rotating, as it is used as part of the gear train. Like most other internal gear systems, Shimano uses tab washers that engage the dropout slot to keep the axle from turning.
Because the shift cable linkage ("cassette joint unit" in Shimano-speak) is also keyed to the axle, there are different types of anti-rotation washers to fit different dropout angles. You need to select the correct type of washers for your particular frame.
(Earlier Nexus hubs only used an anti-rotation washer on the right side, but newer models use a pair of them, each a mirror image of the other.)
The washers are color coded as shown in the chart.
The Nexus hubs were not originally intended for use with bikes that have vertical dropouts. The anti-rotation washers provided with the hub have the wrong orientation for use with vertical dropouts, and originally, Shimano said that these hubs could not be used with vertical dropouts.
Shimano has reconsidered, however, and now makes available an optional set of anti-rotation washers that work with vertical dropouts. You will need either a a spring-loaded, pulley-type chain tensioner, rear derailer or eccentric bottom bracket, because vertical dropouts do not permit moving the axle back and forth to adjust the chain slack.
Note, only the eccentric bottom bracket, not the chain tensioner or rear derailer, will work with the coaster brake version of the Nexus hub, because backpedaling places the lower run of the chain under high tension.
I have a very nice 1970's Raleigh Competition racing frame which I converted into a Nexus 7-speed:
Sheldon Brown's Nexus Raleigh Competition
That worked out so nicely that I converted my early '70s Raleigh International, using a Nexus 8-speed.
I like the Nexus 8-speed a lot better than the 7-speed version.
Sheldon Brown's Nexus Raleigh International
Ideally, the frame should have a drop-out spacing of 127 to 135 mm to fit one of the Nexus hubs. Older bicycles are typically narrower than that. In the case of steel (Cromoly) frames, it is usually possible to spread the rear triangle to the needed width. Any good bicycle mechanic will be able to do this, or you can do it yourself.
If you leave off the Rollerbrake ®, you can get the spacing down to about 126 mm. This is what I did on my Nexus bike. The Rollerbrake ® is a separate module, and when you buy the hub it is not even installed. (The brake unit would get in the way of fitting the spokes through the hub flange, so it has to be installed after the wheel has been built.)
The Alfine 11-speed is oil-lubricated, but the other Nexus and Alfine hubs are packed with a special grease as sold. Mechanical problems can result from "preventive maintenance" including re-lubrication with incorrect grease. This is especially the case if a hub has a coaster brake, due to the heat this brake generates.
The hub must be disassembled into its major components, solvent cleaned, dried and re-lubricated.
Metal wear particles contaminate the grease, and so the hubs require periodic cleaning and replenishment of a special grease that does not make the pawls stick. Still, frequent failures of grease-lubricated hubs due to water contamination have been reported in wet climates --see photos here. Conversion to oil lubrication avoids this problem and also allows replenishment of the lubricant without dismantling the hub.
More information about oil lubrication is in the main file about internal-gear hubs.
Dismantling the Nexus and Alfine hubs is not as difficult as you might think, because of their modular construction.
If you unscrew everything that is screwed onto the left end of the axle, the whole mechanism can be pulled out of the right side as a unit.
These hubs have a rotary shifter rather than a shifter rod in a hollow axle, and so you can't add oil by squirting it into the end of the axle. To replenish oil between rebuilds, you must either unscrew the left bearing cone (which requires removing the wheel from the bicycle) or else add an oiling port, such as a Sturmey-Archer oil cap.
A Shimano Rollerbrake is lubricated without any disassembly, using the special Nexus brake grease -- there's a small rubber access plug on the side of the brake unit, just pop off the plug, put the nozzle of the grease tube up against it, and squeeze.
Shimano Tech Tips -- structure and function, troubleshooting charts etc.
Shimano Nexus lubricants.
|Harris Cyclery carries Nexus-equipped bicycles
from several manufacturers, including:
|Articles by Sheldon Brown and others|