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The Shimano Nexus 4-Speed Hub

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by Sheldon "What Four?" Brown
and
John "Fourgone" Allen Spoke Divider
Shimano Nexus 4-speed hub

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

General information

The Nexus 4-speed hub is a discontinued product. We provide information about it here for the sake of completeness and to assist people who who would like to keep this hub in service.

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.

Gear range

Nexus is a family of parts, of which the Nexus Inter 4 four-speed hub is one.

The overall range of the Nexus four-speed is 184%.

Because the four-speed hub only gears up, it needs a smaller chainwheel and/or larger sprocket than most other internal-gear hubs to achieve a desirable range of drive ratios:

Ratio 1.000 1.244 1.500 1.843
Step 24.4% 20.6% 22.9%  


For comparison, your old 3-speed had a range of 178%:

Ratio 0.750 1.000 1.333
Step 33.3% 33.3%  
 

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

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How it works

The four-speed hub has planetary gearing with a unity ratio and three increase ratios. Its operation is very similar to that of gears 5 through 8 of the Nexus 8-speed hub. A more detailed description is provided in another article on this site.

Installation and Rebuilding Instructions

The 4-speed hub was available in a version with a coaster brake, and a freewheeling version which could optionally host an external Shimano Rollerbrake. There is a page on this site with detailed information about Rollerbrakes.

Shimano lists the overlocknut distance of the 4-speed freewheeling brake hubs as 130 mm, as sold -- see Shimano's overlocknut spacing chart. If not using a Rollerbrake, it is possible to reduce the overlocknut distance by using a thinner lockwasher, as described on the Rollerbrakes page.

The only rebuilding instructions we could find are for a freewheeling version, and in German. The procedure should be clear enough from the images.

The internal mechanism of these hubs is complicated, and the usual repair is to replace it in its entirety.

The right-hand hub bearing cup is vulnerable to damage from water contamination. Better lubrication is recommended to forestall this problem and to make cleaning and rebuilding easier.

The 4-speed hub uses the same cassette joint as the 7-speed hub.

The shift lever for the 4-speed hub is discontinued, but the cable pull for the shift levers for Shimano 7-speed and 8-speed internal-gear hubs is close enough in the lowest 4 gears that these shifters can be used with the 4-speed.

The 4-speed hub was sold for a short time with an automatic, electronic shifting system.

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Model Features Documentation
Nexus SG-4C35 Coaster brake Parts list, exploded drawing
Installation instructions
Nexus SG-4R35 Freewheeling/Rollerbrake Parts list, exploded drawing
Installation instructions
Nexus SG-4R31 Freewheeling/Rollerbrake Rebuilding instructions (in German)
AUTO-D Electronic shifting for 4-speed hub Assembly manual

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Converting an Existing Bicycle:

In some cases, it is possible to convert an existing bicycle to use a Nexus hub. Sheldon had a very nice 1970's Raleigh Competition racing frame which he converted into a Nexus 7-speed.

Sheldon Brown's Nexus Raleigh Competition

Sheldon Brown's Nexus Raleigh Competition

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Links:

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

nexus-greases
Shimano Nexus lubricants.
Harris Cyclery carries Nexus-equipped bicycles
from several manufacturers, including:

Breezer Bicycles

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

Hubs to upgrade existing bikes

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