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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
Shimano Nexus 3, 7 and 8-speed hubs are currently in production as of 2013; the 4-speed has been dropped. Alfine is a high-end product line with 8 and 11-speed hubs. Alfine hubs feature lower internal drag and fancy features including optional hydraulic disc brakes and electronic shifting.
Nexus 7 and 8-speed hubs have an overlocknut spacing ranging from 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 124 mm, using a thinner locknut.
Alfine hubs have an overlocknut spacing of 135 mm.
Shimano sells shifters for these hubs only for flat handlebars, but aftermarket shifters are available to fit drop bars.
The large outer bearing cup at the right side of the Shimano 7- and 8-speed hubs is vulnerable to contamination with water, though Shimano has improved its dustcaps over the years. If the bearing cup becomes pitted, the hub shell must usually be replaced. Then it is usually most practical to replace the entire wheel.
(The right-side bearing cup of some 8-speed hubs is, however, indicated as a replaceable part. If you succeed in replacing one, please let us know how!)
Relubrication using oil and waterproof grease is highly recommended to keep water out of the mechanism. Coaster-brake hubs, however, cannot be oil lubricated; they must be lubricated with a special high-temperature grease.
Nexus and Alfine hubs use the same 3-spline sprockets as other internal gear hubs from Sturmey-Archer and SRAM/Sachs, also used on most coaster-brake hubs.
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. A larger sprocket requires a longer chain.Alfine sprockets include a protector ring which helps to prevent a loose chain from coming off. This is especially helpful if the hub is used with vertical dropouts and a chain tensioner.
Most sprockets made for this system are "dished" so you can adjust the chainline by flipping the sprocket over. Because the shifter mechanism is between the right-side dropout and the sprocket, the chainline is desirably narrow in spite of the large overlocknut spacing of these hubs.
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.
The circlip snaps on, also most easily by levering it into position with a flat-blade screwdriver. Sturmey-Archer circlips, made of round cross-section wire, are easier to install than the Shimano ones with a square cross-section.
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.
Alfine hubs have the Shimano CenterLock fitting, which accepts a proprietary Shimano disc brake rotor. Cable-operated and hydraulic disc brakes are available.
Nexus 3, 7- and 8-speed internal gear systems may incorporate all-weather braking systems. They are available in two forms:
Both of these systems work as well in rain and snow on a sunny spring afternoon, but they also have their limitations. A coaster brake can easily skid the rear wheel, but is hard to control and overheats on long downhill runs. A Rollerbrake is easier to control but may not be as powerful, and also may overheat. See the separate articles on this site about coaster brakes and Rollerbrakes.
Nexus 3-speed hubs are shifted using a bellcrank and pushrod, as described in the article about the 3-speed hubs.
Nexus and Alfine hubs with 4 or more speeds use a "cassette joint", a pulley between the right dropout and the sprocket, concentric with the axle -- a protected location which also moves the sprocket inboard, resulting in a conservative chainline despite these hubs' large overlocknut dimension.
Cassette joint parts are the same for the 4- and 7-speed hubs; different for the 8 and 11-speed hubs. See this document describing differences.
The photo below shows cassette joint parts for an 8-speed hub, from left to right, the driver cap, cassette joint and cassette joint fixing ring. The 11-speed hub also uses a driver cap; the 4 and 7-speed hubs use none.
The photos below show the steps in installation of the cassette joint on an 8-speed hub.
1. Sprocket and sprocket circlip are installed before the cassette joint parts.
2. The driver cap snaps on, concave side down.
3. The cassette joint is installed either of two ways, so the red dots line up.
4. The cassette joint fixing ring is installed so the yellow dots line up. Turn it clockwise to lock it.
Adjustment is made with the shifter in 4th gear for the 4, 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 the "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 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.
The axle flats and washer tab are not in line with each other, as with Sturmey-Archer and Sachs/SRAM hubs, and so you may have to file the dropout slots of an older bicycle to fit a Nexus hub. File only the lower edge of the dropout slots, to avoid disturbing wheel alignment. You may check your work using an anti-rotation washer: if the tab of the washer fits, the axle will fit. Except with vertical dropouts, the tab should preferably face the closed end of the dropout slot.
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 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 5R and 7L are nearly identical, as are the 5L and 7R, and so these pairs may be interchanged by switching sides. The 6R and 6L also may be used on the "wrong" sides of the hub for the best cable alignment with some bicycles. The 8L and 8R may be useful with forward-facing dropouts if you would like to run the cable up a seatstay.
The washers are color coded as shown in the chart.
There is another anti-rotation washer chart on the Shimano site, and it may be easier to read.
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 124 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. Oil lubrication, with waterproof grease for the outer bearings, 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.
Removing and replacing the internals of 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|