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Shimano Nexus and Alfine 8-Speed Hubs

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by Sheldon "All Fine with Me" Brown
revised by John "...Roku...Nana...Hachi" Allen
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Nexus Hub Cutaway

New! On-line Gear Calculator for Internally-Geared Hubs

General information

Another article on this site covers maintenance issues that apply to 4-, 7-, 8- and 11-speed Shimano Nexus and Alfine hubs:

There are also articles on this site more generally about

Read those articles along with this one. For more-detailed advice on installation of sprockets and setting the gear range, see the section on sprockets in the main article on internal-gear hubs.

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Gear range

Nexus is a family of parts, of which the Nexus Inter 8 eight speed hub is one. The Alfine 8-speed hub is a very similar, higher-end model, with dual roller clutches and needle-bearing pinions.

The overall range of the Shimano 8-speed hubs is 307%:

Ratio 0.527 0.644 0.748 0.851 1.000 1.223 1.419 1.615
Step 22.3% 16.0% 13.9% 17.5% 22.3% 16.0% 13.9%  
 

For comparison, the Nexus 7-speed hub as a range of 244%:

Ratio 0.632 0.741 0.843 0.989 1.145 1.335 1.545
Step 17.3% 13.8% 17.3% 15.8% 16.6% 15.8%  
 

Does the hub need repair?

The Nexus 8-speed is more rugged than the 7-speed, but it has some well-known failure modes, and there are also well-known ways to prevent failure.

Aaron, of Aaron's Bicycle Repair, reports:

A "clunk" now and again on a Shimano 8 speed hub is normal. It is the sun gear rotating and engaging the axle pawl. Even if you pedal lightly it will make that noise/feeling but not as loud. The harder you pedal during shifting or right after, the louder the noise. It can change as the hub gets older. Full cleaning and lubing usually restores like new function but is expected that there will be slight differences in the noise over time.

Sometimes the shift spring on the axle can get weak or the axle sleeve that lifts the pawls can get sticky as it wears. I have solved the problem by replacing the axle unit or rebuilding it.

Care should be taken to release force on the pedals when shifting. Applying power to a pawl which is partly engaged can damage the pawl. Shock loads have also broken other parts of the axle assembly. Aaron has photos of axles showing typical failures. He also recommends not standing to pedal on hills. Instead, shift down and spin.

Probably the most common failure, though, is due to insufficient lubrication, leading to contamination by water and dirt. That comment leads into our next topic...

Installation and Rebuilding Instructions

The table below lists models in each series of Shimano 8-speed hubs in order from newest to oldest.

These hubs have a overlocknut spacing ranging of 132 to 135 mm, as sold; -- see Shimano's overlocknut spacing chart. It is possible to reduce the spacing by leaving off the Rollerbrake and using a narrower locknut. See our Rollerbrake page for instructions.

These hubs have gone through several minor design changes, resulting in new model numbers and parts incompatibilities. Model numbers are in the form SG-8Rxx --: example, SG-8R20. The first of the two digits after the "R" represents the series, reflecting the number of roller clutches and whether the hub has cable shifting or electronic shifting. The greatest compatibility is within each series.

The right-hand column in the table below holds links to available information about these hubs. Shimano has rebuilding instructions available only for one model, though others are similar. Several models are documented only by compatibility information in parts lists for other models.

The internal mechanism of these hubs is complicated, and the usual repair is to replace the mechanism in its entirety. Shimano indicates little compatibility with hub shells of different models -- see the last two pages of this document, but the internal mechanism can usually be replaced with a newer version as long as the hub is in the same series (with or without coaster brake; same number of roller clutches contacting the shell -- but also be aware of other minor differences, which may be reflected in the design of the shell). See this Shimano document for description of some internal differences. I haven't had the opportunity to experiment, but I suspect that Alfine shells are largely compatible with parts for Nexus hubs that have two roller clutches contacting the shell, and vice versa. A third roller clutch inside the mechanism of premium models does not affect shell compatibility.

Shimano sells the axle assembly only as a unit and does not provide rebuilding instructions for it -- but you might disassemble it either by mistake or to cannibalize parts. Rebuilding instructions for the axle assembly are available, on the Web site of Aaron's Bicycle Repair.

The right-hand hub bearing cup is vulnerable to damage from water contamination. Better lubrication than is provided at the factory is recommended -- even with a new hub -- to forestall this problem and to make cleaning and rebuilding easier. The right-hand bearing cup is listed as a replaceable part in some parts lists. The old one would have to be extracted and a new one pressed in. If you succeed with this, please send advice, because that repair can save a wheel!

Do not lubricate the cassette joint (cable attachment parts)-- see advice in the Nexus technical article.

Most parts lists linked in the table below include some compatibility information, and many are formatted similarly so that you can compare them visually (like an astronomer looking at two sky photos in a "blink comparison" when searching for an exploding star or an asteroid).

Click here for an On-line Gear Calculator for Internally-Geared Hubs

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Model Features Documentation
Alfine SG-S505 Two external roller clutches, CenterLock rotor fitting, electronic shifting; mostly compatible with S501.

Parts list, exploded drawing
Dealer manual

Alfine SG-S501

Two external roller clutches, CenterLock rotor fitting; backwards-compatible with S500. Parts list, exploded drawing
Installation instructions

Alfine SG-S500

Two external roller clutches, CenterLock rotor fitting; mostly interchangeable with S501. Parts list, exploded drawing
Installation instructions
Alfine
WH-S500-8D
8-Speed rear wheel; CenterLock rotor fitting; two roller clutches Parts list, exploded drawing
Installation instructions
Alfine
WH-S500-V-8D
8-Speed rear wheel; CenterLock rotor fitting; two roller clutches Parts list, exploded drawing
Installation instructions
Nexus SG-8C56 One roller clutch, coaster brake Parts list, exploded drawing
Installation instructions
Nexus SG-8C45 One roller clutch, coaster brake Parts list, exploded drawing
Nexus SG-8C31 One roller clutch, coaster brake Parts list, exploded drawing
Installation instructions
Nexus SG-8C22 One roller clutch, coaster brake Parts list, exploded drawing
Nexus SG-8C20 One roller clutch, coaster brake

Parts list, exploded drawing.
Complete shop manual, in English

Nexus SG-8R56 Electronic shifting, two external roller clutches, Rollerbrake/brakeless Parts list, exploded drawing
Installation instructions
Nexus SG-8R55 Electronic shifting, two external roller clutches, Rollerbrake/brakeless Parts list, exploded drawing
Nexus SG-8R45 Electronic shifting, one roller clutch, Rollerbrake/brakeless Parts list, exploded drawing
Nexus SG-8R36 Two external roller clutches, Rollerbrake/brakeless Parts list, exploded drawing
Nexus SG-8R35 Two external roller clutches, Rollerbrake/brakeless Parts list, exploded drawing
Installation instructions
Nexus SG-8R31 Two external roller clutches, Rollerbrake/brakeless Parts list, exploded drawing
Installation instructions
Nexus SG-8R30 Two external roller clutches, Rollerbrake/brakeless Parts list, exploded drawing
Installation instructions
Nexus SG-8R27 One roller clutch, Rollerbrake/brakeless Parts list, exploded drawing
Installation instructions
Nexus SG-8R25 One roller clutch, Rollerbrake/brakeless Parts list, exploded drawing
Installation instructions
Nexus SG-8R22 One roller clutch, Rollerbrake/brakeless Parts list, exploded drawing
Installation instructions
Nexus SG-8R20 No roller clutch, Rollerbrake/brakeless

Parts list, exploded drawing
(and for the belt-drive version)
Installation instructions
Rebuilding instructions, Shimano site
Rebuilding instructions, on this site

Complete shop manual, in German

Nexus WH-8R25 8-Speed Rear Wheel; for rim brakes only; two external roller clutches Parts list, exploded drawing
Installation instructions

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Converting an Existing Bicycle

In some cases, it is possible to convert an existing bicycle to the use of a Nexus hub.

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

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

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.)

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Links:

Shimano Tech Tips -- structure and function, overhaul, troubleshooting charts etc. -- older page

Shimano Dealer's Manual/User Manual list -- newer page, no rebuilding information

nexus-greases
Shimano Nexus lubricants.
Harris cyclery carries Nexus-equipped bicycles
from several manufacturers

Aaron's Bicycle Repair, Seattle, Washington, USA -- specializes in internal hubs

Hubs to upgrade existing bikes

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