Shimano’s BR-R7070 [paid link] hydraulic disc brakes are known for their consistent stopping power and reliability in a wide variety of conditions. However, like all hydraulic braking systems, they can occasionally develop issues that affect their performance. One of the most common complaints among cyclists is the feeling of sponginess in the brake lever. This issue can be frustrating, as it leads to reduced braking performance, which can compromise safety. In this guide, we’ll explore why your Shimano BR-R7070 [paid link] disc brakes might feel spongy and how to fix this problem quickly.
Understanding the Spongy Brake Lever Issue
A spongy brake lever generally occurs when there is excessive air in the hydraulic brake lines or when the brake fluid level [paid link] is low. In both cases, the hydraulic system cannot generate the proper pressure, leading to a feeling of softness or excessive travel in the brake lever. Let’s dive deeper into the specific causes and solutions.
Possible Causes of Spongy Shimano BR-R7070 Disc Brakes
- Air in the Hydraulic Lines
The most common reason for spongy brakes is air trapped in the brake lines. Air bubbles can interrupt the hydraulic fluid’s ability to transfer pressure, leading to inconsistent braking force and a spongy lever feel. This usually occurs when the brakes are first installed or if the hydraulic system has been opened for maintenance. - Low Brake Fluid
If the brake fluid has been allowed to deplete over time, the hydraulic system may not function correctly. This can happen gradually or due to a leak in the system. Low fluid levels prevent the brake pistons from making firm contact with the rotor, leading to reduced braking force and a spongy lever feel. - Brake Pads Wear
As your brake pads wear down, the distance between the brake pistons and the rotor increases. This causes more lever travel, which can sometimes be mistaken for sponginess, particularly if your pads are worn unevenly. In severe cases, the pistons may not fully retract, causing improper brake feel. - Incorrect Brake Setup
Misalignment of brake components, such as the brake pads, caliper, or rotor, can lead to a lack of proper brake response. This misalignment may cause the lever to feel spongy, as there is not enough contact with the rotor during braking. - Contaminated Brake Fluid
Brake fluid that has been exposed to moisture, dirt, or other contaminants can lose its viscosity and affect the performance of the hydraulic system. Contaminated fluid can cause erratic braking performance and a spongy lever.
How to Fix Spongy Shimano BR-R7070 Disc Brakes
1. Bleeding the Brakes
One of the most effective solutions to fix spongy brakes is to bleed the Shimano BR-R7070 [paid link] hydraulic disc brakes. This process removes air bubbles from the brake lines and ensures the brake fluid is at the correct level [paid link].
Steps to Bleed Shimano BR-R7070 Disc Brakes:
- Step 1: Gather your tools, including Shimano’s specific brake fluid (mineral oil [paid link]), bleed kit [paid link], and a 7mm wrench.
- Step 2: Position the bike securely and remove the wheel to gain access to the brake caliper.
- Step 3: Attach the bleed block to the caliper to protect the pistons.
- Step 4: Remove the brake lever’s reservoir cap and fill it with brake fluid.
- Step 5: Connect the bleed syringe to the caliper’s bleed port, making sure the brake lever is positioned in the correct angle.
- Step 6: Begin the bleeding process by pressing the syringe, allowing air bubbles to escape from the brake lines.
- Step 7: Once no air bubbles remain and the brake fluid is clear, close the bleed port and remove the syringe.
- Step 8: Reinstall the brake reservoir cap, check fluid levels, and test the brake lever feel.
Bleeding the brakes should eliminate any trapped air and restore your Shimano BR-R7070’s braking power.
2. Check and Top-Up Brake Fluid
If low brake fluid is causing the sponginess, simply topping up the fluid may restore the correct brake feel. This process is part of regular brake maintenance, and you should always use Shimano’s recommended mineral oil [paid link].
Fluid Topping Steps:
- Step 1: Remove the brake lever’s cap.
- Step 2: Check the fluid level [paid link] inside the reservoir; if it’s low, add the appropriate amount of Shimano mineral oil [paid link].
- Step 3: Reinstall the cap tightly and check for any leakage.
- Step 4: Test the brake lever to ensure it feels firm and responsive.
Make sure to monitor the fluid level regularly to avoid any further spongy feel in the future.
3. Inspect Brake Pads and Pistons
Check the brake pads for excessive wear. If the pads are thin or uneven, replace them immediately. In some cases, worn brake pads cause the brake lever to feel spongy because of the increased lever travel needed for the pistons to contact the rotor.
How to Check and Replace Brake Pads:
- Step 1: Remove the wheel to gain access to the caliper and brake pads.
- Step 2: Check the thickness of the pads. If they are less than 1mm thick, replace them.
- Step 3: To replace the pads, remove the retaining pin or clip holding the pads in place.
- Step 4: Slide the new pads into place and reassemble the caliper.
- Step 5: Reinstall the wheel and test the braking system.
4. Inspect and Replace Contaminated Brake Fluid
If the brake fluid appears contaminated or has been exposed to air or moisture, it’s time to replace it. This is typically done when performing a brake bleed, but it’s important to check the condition of the fluid before bleeding the system.
Steps to Replace Brake Fluid:
- Step 1: Use a syringe to remove any old fluid from the brake system.
- Step 2: Clean the brake components thoroughly.
- Step 3: Refill the system with fresh Shimano mineral oil [paid link] and bleed the brakes to eliminate any remaining air.
Preventing Spongy Brake Feel in the Future
- Regularly check brake fluid levels to ensure the system remains at its optimal performance.
- Perform routine brake maintenance every 3-6 months, depending on riding conditions.
- Replace brake pads when they are worn down to maintain proper brake engagement.
- Bleed the brakes if you notice any change in brake lever feel, especially after bike disassembly, crashes, or long periods of storage.
By following these steps, your Shimano BR-R7070 hydraulic disc brakes will remain responsive and firm, ensuring optimal stopping power during every ride.