Are your mountain bike brakes feeling spongy? This common issue can be frustrating and potentially dangerous when out on the trails. Spongy brakes can compromise your ability to stop quickly and effectively, putting you at risk of accidents and injury. Fortunately, there are several potential causes for spongy brakes, as well as solutions to get them back to optimal performance.

One common reason for spongy brakes is air in the brake lines. Air can enter the system when brakes are not bled properly or if there is a leak somewhere in the brake system. This air can compress, leading to that spongy feeling when you pull the brake lever. Bleeding the brakes to remove any air and ensure a solid connection between the pads and rotors can help restore proper brake function.

Another possible cause of spongy brakes is contaminated brake fluid. Dirt, water, or other contaminants can get into the brake fluid, causing it to lose its ability to effectively transfer force from the brake lever to the calipers. Flushing the brake system and replacing the fluid can help eliminate sponginess and improve brake performance.

Check Brake Pads

Inspect the brake pads for wear and tear.

If the pads are worn down beyond their limit, replace them immediately.

Check for any contaminants on the pads, such as oil or dirt, and clean them if necessary.

Ensure the pads are properly aligned and making full contact with the braking surface.

• If the pads are misaligned, adjust them accordingly.
• If the pads are not contacting the braking surface evenly, realign them.

Make sure the pads are securely attached to the caliper and are not loose or damaged.

If the pads are damaged or loose, replace them to ensure proper braking performance.

Inspect Brake Cables

Check the brake cables for any signs of wear or damage such as fraying, kinks, or rust.

Step 1

Make sure the cables are properly seated in the cable housing and that there are no sharp bends that could affect the braking performance.

Step 2

Ensure that the cables are properly tensioned and adjust if necessary using the barrel adjusters.

Issue	Possible Cause	Solution
Spongy brakes	Loose or damaged brake cables	Inspect and replace damaged cables, adjust tension

Bleed the Brakes

If your MTB brakes feel spongy, it may be due to air bubbles trapped in the brake lines. To solve this issue, you will need to bleed the brakes. Follow these steps to properly bleed your MTB brakes:

1. Start by making sure your bike is stable and secure.
2. Remove the wheel and place a container underneath the brake caliper to catch any brake fluid that may leak.
3. Locate the bleed screw on the brake caliper – it is usually a small screw with a rubber cover.
4. Attach a bleed kit to the bleed screw and loosen the screw slightly.
5. Fill the syringe in the bleed kit with fresh brake fluid.
6. Squeeze the brake lever a few times to push out any air bubbles in the brake line.
7. Slowly turn the bleed screw to release any air bubbles along with the old brake fluid.
8. Continue this process until you see only clean brake fluid coming out of the system.
9. Tighten the bleed screw, remove the bleed kit, and wipe off any excess brake fluid.
10. Reinstall the wheel and test the brakes to ensure they feel firm and responsive.

Check Brake Fluid Levels

One common reason for spongy MTB brakes is low brake fluid levels. To check the brake fluid levels, you will need to locate the brake fluid reservoir on your bike. This can usually be found near the brake lever or caliper.

Steps to check brake fluid levels:

1. Clean the reservoir: Before checking the fluid levels, make sure to clean the reservoir and its surroundings to prevent dirt or debris from contaminating the brake fluid.

2. Open the reservoir cap: Use a screwdriver or the appropriate tool to carefully open the reservoir cap. Be cautious not to let any dirt or contaminants fall into the reservoir.

3. Check the fluid level: Look inside the reservoir to see if the brake fluid level is between the “min” and “max” markings. If the level is below the minimum mark, it’s time to refill the brake fluid.

4. Refill if necessary: If the brake fluid level is low, carefully add the appropriate type of brake fluid to bring it back up to the recommended level. Be sure to use brake fluid recommended by the manufacturer of your bike.

Adjust Brake Lever Reach

To adjust the reach of your brake levers, follow these steps:

Step 1: Identify Adjustment Screw

Locate the reach adjustment screw on your brake lever. It is usually located near the pivot point of the lever.

Step 2: Turn Adjustment Screw

Using a screwdriver or Allen key, turn the adjustment screw clockwise to move the lever closer to the handlebar, or counterclockwise to move it further away.

Replace Brake Hoses

If your MTB brakes feel spongy and you have already tried bleeding them with no improvement, it might be time to replace the brake hoses. Over time, brake hoses can become worn, cracked, or damaged, leading to a decrease in braking performance. Here’s how you can replace them:

1. Gather Your Tools

Before you begin, make sure you have the necessary tools on hand. You will need a set of replacement brake hoses, a set of new olives and inserts, a set of new barbs, a 5mm or 6mm hex key (depending on your brake model), and a tubing cutter or sharp knife.

2. Remove Old Brake Hoses

Start by removing the old brake hoses from your brake calipers and levers. Use the hex key to loosen the fittings and carefully remove the hoses. Be sure to catch any brake fluid that may leak out during this process and dispose of it properly.

Check for Air in the Brake System

Step 1: Start by inspecting the brake lines and connections for any signs of leaks or damage. If there are any visible issues, address them before proceeding.

Step 2: Bleed the brake system to remove any air bubbles that may be causing the sponginess. Use a bleed kit and follow the manufacturer’s instructions carefully.

Step 3: Test the brakes by squeezing the lever while the bike is stationary. If it feels spongy, repeat the bleeding process until the lever feels firm and responsive.

Step 4: Check the brake pads for wear and replace them if necessary. Worn brake pads can contribute to spongy brakes and reduced stopping power.

Step 5: If the issue persists, consider taking your bike to a professional mechanic for further inspection. They may be able to identify any underlying problems that are causing the sponginess in your MTB brakes.

Replace Brake Calipers

To replace brake calipers on your MTB, follow these steps:

1. Remove the wheel by loosening the bolts or quick release mechanism.
2. Unscrew the caliper mounting bolts and detach the caliper from the bike frame.
3. Install the new caliper in the same position as the old one and tighten the mounting bolts securely.
4. Adjust the position of the caliper so that the brake pads are aligned with the rotor properly.
5. Reattach the wheel and test the brakes to ensure they are functioning correctly.

Check Brake Rotors for Wear

Inspect the brake rotors for any signs of wear, such as grooves or scoring. If you feel any roughness on the surface, it may indicate that the rotors are worn out and need to be replaced.

Check for any discoloration or heat spots on the rotors, as this can also indicate wear and may affect braking performance.

If the rotors are warped or have uneven thickness, it can cause the brakes to feel spongy. In this case, you will need to get the rotors trued or replaced to ensure proper braking power.

Inspect Brake Lever Assembly

Check the brake lever for any visible damage or signs of wear. Make sure it is securely attached to the handlebar and that the lever action is smooth and consistent.

Inspect the brake cable for any kinks, fraying, or signs of corrosion. Ensure that the cable is properly tensioned and that it moves freely within the housing.

Check the brake lever adjustment to ensure that it is within the recommended range. Make any necessary adjustments to improve brake performance.

Inspect the brake lever pivot point for any signs of excessive play or wear. Lubricate the pivot point if needed to ensure smooth operation.

Ensure that the brake lever is compatible with your brake system and that it is properly matched to the type of brake caliper you are using.

Test Brakes for Proper Functionality

1. Start by squeezing the brake lever to see if there is any resistance. If the lever feels spongy or goes all the way to the handlebar, this indicates air in the brake lines.

2. Check for any leaks in the brake system by inspecting the calipers, hoses, and connections for signs of fluid.

3. Test the responsiveness of the brakes by applying gradual pressure to the brake lever while riding slowly. Ensure that the brakes engage smoothly and bring the bike to a stop without any delay.

4. If the brakes are still spongy, try bleeding the brake system to remove any air bubbles. This process involves adding new brake fluid and purging any trapped air from the lines.

5. After bleeding the brakes, re-test the functionality to ensure that they are now firm and responsive. Make any necessary adjustments to the brake pads or calipers if needed.