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 7 seven speed hub is one.

The overall range of the Nexus 7-speed is 245%:

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%

 

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

Ratio	0.750		1.000		1.333
Step		33.3%		33.3%

 

Wouter Pasman has posted an article in PDF format on the Web describing the workings of the Nexus 7-speed. It's a bit technical but if that's what you want, there you go. Thanks, Wouter!

The table below lists models of first, coaster brake, then freewheel/Rollerbrake Shimano 7-speed hubs from newest to oldest. The table links to current Shimano documents, but also to documents generated outside Shimano, or which Shimano no longer offers.

General information on installation and adjustment of newer Shimano Nexus 7-speed hubs is in the Dealer's Manual.

Shimano 7-speed hubs have a overlocknut spacing from 127 to 130 mm, as sold; -- see Shimano's overlocknut spacing chart. Overlocknut spacing can be reduced somewhat by using a different locknut and omitting the Rollerbrake, as described on the Rollerbrake page.

SG-7 series hubs went through several minor design changes, resulting in new model numbers and parts incompatibilities. The newer C3000-series hubs are significantly different from earlier ones, with pawls on the axle rather than the insides of the sun gears. Rebuilding instructions from Shimano in English are available only for one coaster-brake model and one freewheeling model, though others are similar. Reader Alesu has kindly provided translations from German of technical documents about DG-7 series hubs including rebuilding isntructions for a couple of additional ones. Links in the list below will take you to these documents.

Did you go too far when tearing down a hub? This site also includes information from reader Keith Lang on how to rebuild the axle unit of the 7-speed hub. Wouter Pasman's disassembly/reassembly instructions also include this information.

Replacement parts availability is a concern, and so you may have to substitute an internal assembly from a different model. The internal mechanism of these hubs is complicated, and the usual repair is to replace it in its entirety. It can usually be replaced with a newer version as long as the hub is of the same basic type (with or without coaster brake) and in the same series.

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

Most parts lists 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).

The Shimano Inter-7 hub Dealer's Manual/User Manual page makes many of the documents listed below available in other languages besides English, in case that is your preference.

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

I purchased a Shimano SG-7R40 hub, and installed it on one of my own bicycles, an early '70's Peugeot PX-10 racing bike. My initial impression on actually using one was extremely favorable. I particularly like the RapidFire control unit, which is very easy to use and has a very light touch. I also am pleased at how well-protected the linkage to the hub is. This hub uses a rotating ring operated by the cable, inboard of the chainstay. There are no delicate parts protruding out past the frame, as with other internal-gear hubs. I find the range of gears quite pleasant to use, and the efficiency of the hub doesn't appear to be any worse than the Sturmey-Archer FM four-speed unit it replaced.

My Peugeot "PX-7" has time-trial style "cowhorn" bars, which are a lot like the bottom part of drop bars. The usual orientation for the RapidFire shifter is on the right, hanging below straight bars, where it may easily be operated by the right thumb. The cable runs inward parallel to the bar.

On my Peugeot, I have it on the left side, clamped to the bar just below the brake lever, where it it very convenient to be operated by my left thumb. The cable runs downward, making a neat run toward the down tube of the frame. This works quite well for me. I have a separate page about this bike, with pictures.