Shimano’s BR-R8170 [paid link] hydraulic disc brakes are a popular choice among road cyclists due to their reliable performance and excellent stopping power. However, if you’ve noticed that your brakes feel spongy, you’re not alone. A spongy brake feel can significantly reduce your braking performance and safety on the road. In this article, we’ll explore the reasons behind spongy brake performance in Shimano BR-R8170 [paid link] disc brakes and provide you with step-by-step instructions to fix the issue.
Common Causes of Spongy Brake Feel in Shimano BR-R8170 Disc Brakes
Before you begin troubleshooting, it’s important to understand the possible causes of spongy brake feel. In hydraulic disc brakes, the brake lever pulls fluid from the brake reservoir and pushes it through the brake lines to the calipers, where it activates the brake pads. If there’s air or excess moisture in the hydraulic system, it can cause a spongy or soft feel in the brake lever. Below are the main causes of this issue:
1. Air in the Hydraulic Line
One of the most common causes of spongy brakes is air trapped in the hydraulic lines. When air enters the system, it compresses when you pull the brake lever, resulting in a spongy feel.
2. Low Brake Fluid Levels
If the brake fluid level [paid link] is too low, the brake lever may feel soft or spongy. This can occur if there’s a leak in the hydraulic system or the fluid has evaporated over time due to heat or wear.
3. Moisture Contamination
Moisture contamination can also affect brake performance. If water or other contaminants enter the brake fluid, they can compromise the hydraulic system, leading to a spongy lever feel.
4. Worn Brake Pads or Rotors
Although not directly related to the hydraulic system, worn brake pads or rotors can also make the braking feel less effective, contributing to the sponginess. The system may need to compensate for the reduced contact area, which can feel like a spongy lever.
How to Fix Spongy Shimano BR-R8170 Disc Brakes
Now that you understand the common causes of spongy brakes, let’s walk through the steps to restore your Shimano BR-R8170 [paid link] disc brakes to their optimal performance.
Step 1: Check for Air in the Hydraulic Line
If there is air in the hydraulic line, it must be bled out to restore proper brake function. Shimano provides a simple procedure for bleeding their hydraulic disc brakes, which you can follow.
Tools Needed:
- Shimano hydraulic brake bleed kit [paid link]
- Isopropyl alcohol
- Clean rags
- Brake fluid (Shimano mineral oil [paid link])
- Syringe and hose (included in the kit)
- Bleed block (if required)
Procedure:
- Prepare the bike: Secure the bike in a stand and remove the wheel for better access to the brake calipers.
- Remove the brake pads: Use a 5mm Allen wrench [paid link] to remove the brake pads from the caliper. Insert the bleed block if needed.
- Set up the bleed kit [paid link]: Attach the syringe filled with Shimano mineral oil [paid link] to the brake lever, and connect the other syringe to the caliper.
- Open the bleed port: Using the syringe, slowly push brake fluid into the brake caliper. This will force any air out of the line.
- Check for air bubbles: Watch for bubbles in the fluid as you push it through. Continue until no air bubbles appear.
- Seal the system: Close the bleed port and remove the syringes. Reinstall the brake pads.
- Test the brakes: Reinstall the wheel and test the brakes to ensure the lever feels firm and responsive.
Step 2: Top Up Brake Fluid
If the brake fluid level [paid link] is low, it can also cause a spongy feel. Topping up or replacing the fluid is an easy fix to restore braking power.
Procedure:
- Locate the brake fluid reservoir: The Shimano BR-R8170 has a brake fluid reservoir located on the brake lever.
- Open the reservoir cap: Use the correct tool to open the reservoir cap carefully.
- Check the fluid level [paid link]: If the fluid level is low, top it up with Shimano mineral oil [paid link] until it reaches the recommended level.
- Replace the cap and check for leaks: Ensure the cap is properly sealed to prevent any fluid from leaking out. Test the brakes by squeezing the lever to see if the sponginess is resolved.
Step 3: Inspect for Moisture Contamination
Moisture contamination can weaken the braking system and cause sponginess. If you suspect that moisture has entered the system, you should replace the contaminated brake fluid.
Procedure:
- Bleed the brakes: Perform the brake bleeding procedure outlined in Step 1. During this process, any contaminated brake fluid will be replaced with fresh fluid.
- Test the brakes: After replacing the fluid, test the brakes by squeezing the lever. If the sponginess persists, ensure that all air has been removed during the bleeding process.
Step 4: Check Brake Pads and Rotors
Worn brake pads or rotors may also contribute to a spongy brake feel. If the pads are excessively worn or the rotors are damaged, you may need to replace them.
Procedure:
- Check the brake pads: Inspect the brake pads for wear indicators. If they are below the minimum thickness, replace them with new Shimano-approved pads.
- Inspect the rotors: Check for any warping, scoring, or damage on the rotors. If the rotors are warped, they can cause uneven braking pressure, contributing to sponginess. Replace damaged rotors with Shimano-approved ones.
- Install new pads and rotors: If necessary, install new pads and rotors, ensuring proper alignment and torque specifications.
Step 5: Perform a Final Test Ride
Once all the issues have been addressed, perform a final test ride to ensure the brakes are functioning properly. Pay close attention to the brake lever feel and overall braking performance. If the brakes still feel spongy after completing these steps, it’s recommended to take the bike to a professional mechanic for further inspection.
Conclusion
A spongy brake lever in your Shimano BR-R8170 disc brakes is usually caused by air in the hydraulic line, low brake fluid, moisture contamination, or worn brake pads and rotors. By following the troubleshooting steps outlined in this guide, you should be able to quickly diagnose and resolve the issue, restoring your brakes to their optimal performance. Remember to always check your brake fluid levels, inspect the pads and rotors regularly, and perform periodic brake maintenance to keep your Shimano BR-R8170 disc brakes in top condition.