Troubleshooting Shimano SM-RT900 Disc Brakes: How to Fix Common Braking Issues

The Shimano SM-RT900 [paid link] is a popular choice among road cyclists due to its high-performance features and advanced technology. However, like all disc brake systems, it can encounter common issues that affect braking efficiency. In this guide, we’ll walk you through some of the most common problems with Shimano SM-RT900 [paid link] disc brakes and provide solutions for fixing them. Understanding how to troubleshoot these issues will ensure that your brakes perform optimally for a safer and smoother ride.

Common Problems with Shimano SM-RT900 Disc Brakes

1. Weak Braking Power

Weak braking power is one of the most common complaints among Shimano SM-RT900 [paid link] users. This issue can occur for several reasons, including improper pad alignment, contamination, or worn-out brake pads.

Solution:

Check Pad Alignment: Ensure that the brake pads are aligned with the rotor. Misaligned pads can lead to uneven braking pressure. Adjust the caliper so that the pads are centered on the rotor.
Clean the Pads and Rotor: Oil, dirt, and grime can accumulate on the rotor and brake pads, reducing braking power. Clean both the pads and rotor using isopropyl alcohol or a disc brake cleaner. Avoid using household cleaners as they may leave residue that affects performance.
Replace Worn Brake Pads: If the brake pads are worn down below the minimum thickness, they will need to be replaced. Worn-out pads can significantly reduce braking power and may even damage the rotor.

2. Brakes Making Noise

A noisy brake system can be both annoying and a sign of underlying issues with the Shimano SM-RT900 brakes. Common causes of noise include contamination, pad wear, or rotor deformation.

Solution:

Check for Contamination: Oil or debris on the rotor or pads can cause squeaking or grinding noises. Clean the rotor with alcohol and inspect the brake pads for contamination. If the pads are contaminated, it’s best to replace them.
Ensure Proper Rotor Alignment: A warped rotor can create noise during braking. Use a rotor truing tool to check the rotor’s alignment. If the rotor is bent, gently straighten it using the tool.
Bed-in the Brakes: If your Shimano SM-RT900 disc brakes are new, they may need a proper bedding process. Bedding-in the brakes will create a layer of friction material on the rotor, which can help reduce noise. To bed in your brakes, make a series of gentle braking applications from a moderate speed, gradually increasing the force. Avoid hard braking during this process.

3. Spongy or Soft Brake Feel

A spongy brake lever feel is often caused by air in the hydraulic brake lines or insufficient brake fluid.

Solution:

Bleed the Brakes: The most common cause of a spongy brake feel in hydraulic systems is air trapped in the brake lines. Bleeding the Shimano SM-RT900 brakes will remove any air and restore proper braking feel. Shimano provides a detailed guide on how to bleed their hydraulic brake systems.
Check Brake Fluid: Low brake fluid levels can also lead to poor brake performance. Inspect the fluid level [paid link] in the brake reservoir and top it up if necessary. Always use the recommended Shimano brake fluid to avoid damaging the system.

4. Brakes Pulling to One Side

If your Shimano SM-RT900 disc brakes pull to one side when applied, this is typically a sign of uneven pad wear, caliper misalignment, or rotor issues.

Solution:

Inspect the Brake Pads: Check if the brake pads are evenly worn. Uneven pad wear can occur due to contamination or a misaligned caliper. If the pads are unevenly worn, replace them and realign the caliper.
Align the Caliper: A misaligned caliper can cause the brake to pull to one side. Loosen the caliper mounting bolts and center the caliper over the rotor. Tighten the bolts while ensuring the caliper remains in the correct position.
Check the Rotor: A bent rotor can cause uneven braking, resulting in a pull to one side. Use a rotor truing tool to check for any warping and adjust the rotor if necessary.

5. Brake Fade

Brake fade occurs when the braking performance diminishes during extended braking periods, such as during long descents. This issue is typically caused by overheating of the brake pads or rotor.

Solution:

Avoid Prolonged Braking: To prevent brake fade, try to avoid riding the brakes continuously during long descents. Instead, use controlled braking in intervals to allow the system to cool down.
Upgrade to High-Performance Pads: If brake fade is a frequent issue, consider upgrading to higher-performance brake pads designed for better heat dissipation.
Check Rotor Condition: Warped or damaged rotors can contribute to brake fade. Inspect the rotor for any signs of warping or scoring, and replace it if needed.

6. Rotor or Pad Wear

Excessive wear on the rotor or brake pads can affect braking performance and overall safety. It’s essential to monitor both components regularly.

Solution:

Measure Rotor Thickness: Shimano SM-RT900 rotors have a minimum thickness specification. If the rotor becomes too thin, it will need to be replaced. Regularly check the thickness of your rotor using a caliper.
Replace Brake Pads: Brake pads wear down over time and should be replaced when they approach the wear limit. Shimano SM-RT900 pads should be replaced if the pad thickness is less than 1mm.

Conclusion

Proper maintenance and troubleshooting of your Shimano SM-RT900 disc brakes are essential to ensure safe and reliable performance. Regularly inspect your brakes for common issues such as weak braking, noise, spongy feel, and uneven wear. By addressing these problems promptly, you can maximize the lifespan of your Shimano SM-RT900 disc brakes and enjoy better stopping power on your rides.

Always refer to the manufacturer’s instructions and consult a professional mechanic if you’re unsure about performing any of these troubleshooting steps yourself. With the right care and attention, your Shimano SM-RT900 brakes will continue to deliver the high performance you expect.