Why Your Shimano SM-RT70 Disc Brakes Might Not Be Set Up Correctly and How to Fix Them

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Shimano’s SM-RT70 [paid link] disc brakes are a reliable choice for cyclists who demand precise, consistent braking performance. However, even the most robust braking systems can face setup issues. Whether you’re dealing with poor performance, squeaking, or inconsistent braking, it’s essential to diagnose and resolve setup problems to restore full functionality.

This guide will walk you through the common reasons your Shimano SM-RT70 [paid link] disc brakes might not be set up correctly and how to fix them.

Common Setup Issues with Shimano SM-RT70 Disc Brakes

When the Shimano SM-RT70 [paid link] disc brakes are not functioning as expected, several factors might be at play. These problems often arise due to improper installation, alignment issues, or incompatibilities with other components in your bike’s braking system. Here are the key setup problems you should look out for:

1. Rotor Misalignment

Improper rotor alignment is one of the most common issues with disc brake setups. If your rotor is not perfectly centered in the caliper, it can result in uneven braking pressure and cause the brakes to rub against the pads.

2. Brake Pad Positioning

Incorrect brake pad positioning can cause poor braking performance. If the pads are not aligned properly with the rotor, they may fail to provide the necessary contact area, leading to weak braking force.

3. Improper Brake Lever Feel

If the brake lever feels too soft or spongy, this can indicate air trapped in the hydraulic system, worn-out brake pads, or insufficient brake fluid.

4. Dirty or Contaminated Rotors and Pads

Brake pads and rotors covered in oil, grease, or other contaminants can lead to reduced braking efficiency and cause noise. These substances can also damage the rotor surface, affecting brake performance.

5. Incorrect Rotor Size

Using the wrong size rotor can affect braking power and cause poor performance. Shimano SM-RT70 rotors are designed to fit specific frame and fork standards, so it’s crucial to ensure the correct rotor size for your setup.

How to Fix Setup Issues with Shimano SM-RT70 Disc Brakes

1. Aligning the Rotor

The first step in ensuring proper braking performance is to check the alignment of your Shimano SM-RT70 disc rotor. Here’s how to fix any misalignment:

  • Inspect the Rotor: Spin the wheel and look at the rotor while it turns. If it wobbles or rubs against the brake pads, it’s misaligned.
  • Adjust the Rotor: To fix a warped rotor, carefully bend it back into shape using rotor truing tools. Alternatively, you can use the brake caliper itself to realign the rotor. If the rotor is severely damaged, consider replacing it.
  • Check the Caliper Position: Loosen the caliper mounting bolts, align it with the rotor, and tighten the bolts. Ensure the caliper is positioned centrally relative to the rotor.

2. Adjusting the Brake Pads

If the brake pads are not aligned correctly, follow these steps to adjust them:

  • Check Pad Alignment: With the wheel removed, visually inspect the position of the brake pads. They should be aligned with the rotor and should not rub when the brake lever is released.
  • Align the Pads: Use the caliper’s pad adjustment screws to reposition the pads. You can also adjust the pistons inside the caliper using a tool if needed. Be sure that the pads are parallel to the rotor for even contact.
  • Clean the Pads: If the pads are contaminated, clean them with isopropyl alcohol and a clean cloth. In cases of excessive contamination (such as oil or grease), you may need to replace the pads entirely.

3. Fixing the Brake Lever Feel

A spongy brake lever feel is often caused by air in the hydraulic lines. To address this, follow these steps:

  • Bleed the Brakes: If you suspect air in the hydraulic system, bleeding the Shimano SM-RT70 brakes will remove trapped air. Shimano provides a specific brake bleeding kit, and the process involves attaching the kit to the brake lever and caliper, then pushing fluid through the system until no air bubbles remain.
  • Check Brake Fluid: Low or contaminated brake fluid can also cause poor lever feel. If the fluid is low, refill it with Shimano-approved brake fluid.

4. Cleaning Rotors and Pads

Contamination on your rotor or brake pads can result in reduced performance or noise. To fix this:

  • Clean the Rotors: Use a clean rag and isopropyl alcohol to wipe down the rotor surface. For stubborn grease or dirt, consider using a dedicated disc brake cleaner.
  • Clean the Pads: Similarly, clean the brake pads with alcohol or a specific cleaning solution for brake components. Avoid using any oil-based cleaners, as these can contaminate the pads and rotor.
  • Replace Worn Pads: If the pads are excessively worn or contaminated beyond cleaning, replace them with new Shimano-approved pads to ensure optimal performance.

5. Choosing the Right Rotor Size

Ensure that you’re using the correct rotor size for your Shimano SM-RT70 disc brakes. These rotors are available in several sizes, typically ranging from 140mm to 180mm. The size you need depends on your bike frame, fork, and personal riding style.

  • Check the Frame and Fork Compatibility: Consult your bike’s specifications or the manufacturer’s guide to determine the correct rotor size.
  • Match the Rotor Size to Your Riding Style: Larger rotors (160mm and above) offer better braking power, especially for downhill or aggressive riding. Smaller rotors (140mm) are sufficient for lighter riders or more casual cycling.

6. Caliper and Brake Mount Compatibility

Ensure that your brake caliper is compatible with the frame and fork mounts. Shimano SM-RT70 is compatible with most modern post-mount systems, but it’s important to double-check the specific requirements for your setup.

  • Check the Mounting System: Verify whether your bike uses a post-mount or IS (International Standard) mount system. Shimano SM-RT70 rotors are designed for post-mount, but adapters may be needed for IS mounts.
  • Use the Correct Adapter: If your bike uses an IS mount, make sure to use the correct adapter to ensure that the caliper aligns properly with the rotor.

Conclusion

If your Shimano SM-RT70 disc brakes aren’t performing at their best, it’s likely due to setup issues such as rotor misalignment, improper brake pad positioning, or contamination. By following the steps outlined above, you can troubleshoot common issues and get your brakes functioning like new again. Ensure your setup is correct by regularly inspecting the components, maintaining cleanliness, and addressing issues before they lead to poor performance or safety concerns. Properly set up Shimano SM-RT70 disc brakes will provide you with reliable, high-performance braking on every ride.