The Shimano FH-RS400 [paid link] hub is a popular choice for cyclists seeking a reliable, durable, and smooth-running rear hub. However, like any mechanical component, it is prone to wear and tear over time. One of the most common issues cyclists face with the FH-RS400 [paid link] hub is rough-feeling bearings, which can significantly affect the overall performance of your bike. In this article, we’ll walk you through why your FH-RS400 [paid link] hub bearings may feel rough and provide detailed instructions on how to fix it.

Understanding the Issue: Rough Bearings in Your FH-RS400 Hub

The feeling of roughness in your FH-RS400 hub is often caused by issues with the internal bearings. These bearings are crucial in allowing the freehub to rotate smoothly, so any imperfections or damage can disrupt the fluid motion, creating resistance and affecting your ride quality.

Possible Causes of Rough Bearings

• Dirty or Contaminated Bearings: The most common cause of rough-feeling bearings is the buildup of dirt, grime, or moisture within the bearing assembly. This contamination can make the bearings less smooth and increase friction.
• Worn Bearings: Over time, even the best quality bearings can wear out, leading to roughness. This wear and tear is often exacerbated by neglecting regular maintenance or riding in harsh conditions.
• Improper Adjustment: If the bearing preload (tightness) isn’t set correctly during installation or maintenance, it can cause the bearings to either be too tight or too loose, leading to rough operation.
• Insufficient Lubrication: Lack of proper lubrication within the bearing assembly can also cause roughness. Without the right amount of grease, the bearings may not spin smoothly, causing friction and resistance.

How to Fix Rough Bearings in the Shimano FH-RS400 Hub

To address the roughness in your FH-RS400 hub, you’ll need to properly inspect, clean, and re-lubricate or replace the bearings. Below are the detailed steps to help you fix the issue.

Tools Required

• 10mm socket wrench
• Shimano FH-RS400 freehub removal tool (or compatible tool)
• Grease (high-quality bicycle grease)
• Clean rag or towel
• Bearing grease or oil
• Plastic bearing press [paid link] or a clean hammer (if replacing bearings)
• Small screwdriver or prying tool

Step 1: Remove the Rear Wheel and Freehub

Before working on the bearings, remove the rear wheel from the bike. You’ll need to detach the freehub body from the hub shell.

1. Using your 10mm socket wrench, remove the axle nut.
2. Use a freehub removal tool to disconnect the freehub body from the hub shell. This may involve removing a locking ring that holds the freehub in place.

Step 2: Inspect the Bearings

With the freehub body removed, inspect the bearings for any visible damage or wear. Look for:

• Pitting or scoring on the bearing races.
• Dirt or debris embedded in the grease.
• Excessive play or movement in the bearings when you manually rotate them.

If you notice any of these issues, it’s time to replace the bearings. If the bearings seem in good condition, you can proceed to clean and lubricate them.

Step 3: Clean the Bearing Assembly

Clean the bearing assembly thoroughly to remove any dirt, grease, or debris that may have accumulated.

1. Use a clean rag to wipe down the inside of the hub shell and freehub body.
2. Carefully remove any remaining old grease from the bearing surfaces. Use a rag or small brush to ensure all surfaces are clean.

Step 4: Lubricate the Bearings

After cleaning, it’s essential to lubricate the bearings to ensure they run smoothly. Apply a thin layer of high-quality bicycle grease to the bearings and the bearing races. This will help reduce friction and prevent the bearings from drying out.

• Be careful not to over-lubricate; excess grease can attract dirt and cause further issues.
• If you are replacing the bearings, ensure the new bearings are well-greased before installing them.

Step 5: Adjust the Bearing Preload

One of the most common causes of rough bearings in the FH-RS400 hub is improper preload adjustment. Preload refers to the tension applied to the bearings, which affects their performance.

1. Reinstall the freehub body onto the hub shell.
2. Ensure that the hub axle is aligned correctly, and tighten the axle nuts to the specified torque (refer to Shimano’s specifications).
3. Carefully adjust the preload by tightening or loosening the locknut to ensure the bearings spin freely without excessive play. It’s important to find a balance—too tight will cause drag, and too loose will result in excess play.

Step 6: Reassemble the Hub

Once the bearings are cleaned, lubricated, and the preload is correctly set, reassemble the freehub body onto the hub shell. Make sure all components are securely in place and that the freehub body rotates smoothly.

• Double-check the axle nut to ensure it is tightened to the correct torque specification.
• Spin the freehub body by hand to feel for any rough spots or resistance. If it still feels rough, recheck the bearing adjustment or consider replacing the bearings.

Step 7: Test the Hub on the Bike

Before hitting the road, test the hub on the bike to ensure the roughness is gone. Install the rear wheel back onto your bike and check if the freehub rotates smoothly when you spin the wheel.

If the hub still feels rough, repeat the cleaning and lubrication process, ensuring that the bearings are properly adjusted.

Preventing Rough Bearings in the Future

To keep your Shimano FH-RS400 hub running smoothly and prevent rough bearings in the future, follow these simple maintenance tips:

• Regularly inspect and clean the bearings, especially if you ride in wet or dirty conditions.
• Lubricate the bearings every 6-12 months, depending on usage.
• Pay attention to unusual noises or resistance when pedaling, as this can indicate bearing wear.
• Avoid over-tightening the bearing preload, as this can cause premature wear.

By staying on top of regular maintenance and adjustments, you can ensure your FH-RS400 hub remains smooth and efficient for many years of cycling enjoyment.