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%

 

The table below lists models of each type of Shimano 7-speed hub in order from newest to oldest. The links in the right-hand column are to available information about these hubs.

These hubs have a overlocknut spacing ranging of 127 or 130 mm, as sold; -- see Shimano's overlocknut spacing chart.

The 7-speed hubs have gone through several minor design changes, resulting in new model numbers and parts incompatibilities. Rebuilding instructions are available only for one coaster-brake model and one freewheeling model, though others are similar.

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.

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; same number of roller clutches).

The right-hand hub bearing cup is vulnerable to damage from water contamination. Oil 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).

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.