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[Nexus 7 gear hub] Replace core assembly?

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[Nexus 7 gear hub] Replace core assembly?

Old 03-28-23, 06:28 AM
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Winfried
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[SOLVED] [Nexus 7 gear hub] Replace core assembly?

Hello,

Someone I know rides a bike with an old Shimano Nexus 7 gear hub with a coaster brake, possibly an SG-7C18.

We'd like to remove the coaster brake for a lever-actuated Roller Brake instead. Apparently, this requires replacing the assembly as the two cores are incompatible, ie. you can't install a "lever brake" on a Nexus that used a coaster brake.

To avoid building a new wheel, does someone know if that old hub is compatible with the latest Nexus 7 gear hub for lever brakes (SG-C3001-7R), so that all it'd take is swaping the core assembly and avoid building a new wheel?

Thank you.



---
Edit: It looks like the hubs are incompatible → build a new wheel with a new hub

"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. [] 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."

https://www.sheldonbrown.com/nexus7.shtml

Last edited by Winfried; 04-03-23 at 01:13 AM.
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Old 03-28-23, 03:55 PM
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They are not in any way compatible. If you want a roller brake you need and entire new hub.
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Old 03-28-23, 09:32 PM
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Roller brakes are the stupidest thing ever invented. More drag than the Titanic. LOL.
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Old 03-29-23, 04:34 AM
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Originally Posted by GamblerGORD53 View Post
Roller brakes are the stupidest thing ever invented. More drag than the Titanic. LOL.
I went the roller brake route on my "winter" bike, which was requiring a rear rim change every couple of years. Nexus 8-speed hub.
As a rear brake, the roller is adequate, and I've had no issues with drag. And no rim replacements!


Roller brake replacement for V-brake eliminated rear rim wear.
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Old 04-03-23, 01:12 AM
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Thanks for the infos.

Coaster brakes are very much useful on a handcycle, something I didn't mention.

The goal was actually to add a mid-drive, but it turns out that, unlike Bafang, a Tongsheng is available in a version that's coaster-brake-compatible, so the user won't need to replace the Nexus.
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Old 04-03-23, 02:00 AM
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Originally Posted by GamblerGORD53 View Post
Roller brakes are the stupidest thing ever invented. More drag than the Titanic. LOL.
Disagree. Very good for low maintainence. Not very good for performance.
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Old 04-03-23, 02:04 AM
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Originally Posted by Winfried View Post
Hello,

Someone I know rides a bike with an old Shimano Nexus 7 gear hub with a coaster brake, possibly an SG-7C18.

We'd like to remove the coaster brake for a lever-actuated Roller Brake instead. Apparently, this requires replacing the assembly as the two cores are incompatible, ie. you can't install a "lever brake" on a Nexus that used a coaster brake.

To avoid building a new wheel, does someone know if that old hub is compatible with the latest Nexus 7 gear hub for lever brakes (SG-C3001-7R), so that all it'd take is swaping the core assembly and avoid building a new wheel?

Thank you.



---
Edit: It looks like the hubs are incompatible → build a new wheel with a new hub

"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. [] 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."

https://www.sheldonbrown.com/nexus7.shtml
The main thing is that the roller brake version has external splines on the hub body itself. These are needed for the roller brake to even function. A coaster hub does not have these splines and therefore no simple conversion is possible.
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Old 04-03-23, 03:06 AM
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Originally Posted by ign1te View Post
Disagree. Very good for low maintainence.
For that reason, they're very common in the Netherlands, and Germany.

Incidently, those countries have bike modal shares way higher than the US.
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