The Nexus 4-speed hub is a discontinued product, at least in the USA. 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:

• Anti-rotation Washers
• Brake Types
• Cable Adjustment
• Cable Installation
• General Advice
• Hubs Covered
• Links
• Lubrication
• Sprockets
• Upgrading Existing Bikes
• Vertical Dropouts

There are also articles on this site more generally about

• Internal-gear hubs
• Internal gear theory
• Shimano product lines and buzzwords

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.

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:

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

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.

The four-speed hub was (and in some countries still may be) 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.

The internal mechanism of these hubs is complicated, and the usual repair is to replace it in its entirety. We have rebuilding instructions for both the freewheeling and coaster-brake versions of the hub, translated from the German versions, which were the only ones we could find online. The procedure given does not include information on timing the compound planet gears. Thanks go to Patricia Morris for pointing this out and for the photo below. The red arrow points to the timing mark. The marks on all three gears must point directly outward.

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.

Shimano lists the overlocknut distance of the 4-speed freewheeling brake hubs as 130 mm, as sold -- see Shimano's overlocknut spacing chart -- though also 123.5 mm and 127 mm, in its rebuilding instructions for the freewheeling/Rollerbrake version. 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 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.

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.