Shimano SG-3R40 Nexus Internal Assembly Unit - 170 mm
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Product Information
Full details
The Shimano SG-3R40 Nexus Internal Assembly Unit is an essential maintenance component designed for cyclists who rely on the SG-3R40 internal gear hub system for city commuting. It restores smooth shifting and reliable power transfer to your drivetrain, making it ideal for mechanics or enthusiasts looking to service their own internal gear hubs. Please note that this unit requires specific mechanical aptitude and compatibility verification with your existing hub shell to ensure a perfect fit.
All features
| Model Part Number | 33S9070 |
|---|---|
| Brand | Shimano |
Extended Product Information
FAQs
Is this compatible with coaster brake hubs?
No, this specific assembly is designed for the SG-3R40, which is optimized for roller brake configurations, not coaster brakes.
Do I need special tools to install this?
Yes, you will need a cone wrench set and a standard tool kit for hub disassembly, along with a Shimano-specific internal hub grease.
What is the length of this assembly?
This unit is 170 mm in length, specifically sized for the SG-3R40 hub series.
How often should I service this internal assembly?
For typical city commuting, it is recommended to perform a thorough cleaning and re-greasing at least once a year.
Can I use standard bicycle chain lube inside the hub?
No, you must use high-quality, water-resistant internal hub grease to ensure proper component life and function.
Troubleshooting
Difficulty shifting between gears
Check the cable tension at the shifter and ensure the bell crank is adjusted so the yellow marks align correctly.
Grinding or noisy operation
The unit likely requires a deep clean and fresh application of Shimano-specific internal hub grease.
Hub slips under load
Verify the internal pawls are clean and the gear cable is not frayed or binding within the housing.
Pros and Cons
Pros
- Restores original factory-shifting performance
- High-quality construction from a trusted cycling brand
- Seamless integration with existing Shimano roller brakes
- Extends the functional lifespan of Nexus gear hubs
Cons
- Requires specific tools for hub disassembly
- Not compatible with non-Nexus or non-SG-3R40 hub shells
- Installation can be complex for inexperienced mechanics
Setup, Compatibility & Care
To install this unit, you must first remove the rear wheel and unscrew the left-hand cone nut to extract the old assembly from the hub shell. Before inserting the new 170 mm assembly, inspect the internal shell for debris or old, degraded grease and clean thoroughly. Apply a fresh layer of Shimano internal hub grease to the planetary gears and pawls. Once inserted, carefully tighten the locknut to the manufacturer's recommended torque settings to avoid damaging the bearing races. Regular care includes an annual inspection and re-greasing to prevent the internal components from seizing due to moisture ingress.