Bleeding motorcycle rear brakes manually is a fundamental maintenance task that restores firm brake feel and optimal stopping power by removing trapped air from the hydraulic system. This process ensures your rear brake functions reliably and safely.
Why Bleed Your Brakes?
Over time, air can enter your motorcycle's brake lines through various means, such as fluid changes, component replacement, or even microscopic leaks. Air is compressible, unlike brake fluid, leading to a "spongy" brake pedal feel and reduced braking effectiveness. Bleeding removes this air, allowing the hydraulic system to work efficiently.
Tools and Materials Required
Before you begin, gather all necessary tools and supplies to ensure a smooth and efficient bleeding process.
- New Brake Fluid: Always use the type specified in your motorcycle's owner's manual (e.g., DOT 3, DOT 4, DOT 5.1). Never mix different DOT types unless specifically permitted, especially DOT 5 (silicone-based) with others.
- Clear Plastic Tubing: Approximately 2-3 feet of tubing that fits snugly over the bleed nipple.
- Wrench: Open-end wrench or a flare nut wrench (recommended) that fits your bleed nipple (common sizes are 8mm, 10mm, or 11mm).
- Container: A small, clear container (e.g., a jar or bottle) to collect old brake fluid.
- Rag/Shop Towels: For wiping spills and protecting painted surfaces. Brake fluid can damage paint.
- Gloves: To protect your hands from brake fluid.
- Eye Protection: Safety glasses are essential.
- Optional: A turkey baster or syringe to remove old fluid from the reservoir.
Brake Fluid Compatibility Chart
Understanding brake fluid types is crucial for safety and system compatibility.
| Brake Fluid Type | Base | Boiling Point (Dry) | Key Characteristics |
|---|---|---|---|
| DOT 3 | Glycol | 205°C (401°F) | Standard, common, absorbs moisture, compatible with DOT 4/5.1. |
| DOT 4 | Glycol | 230°C (446°F) | Higher boiling point than DOT 3, common in modern motorcycles, absorbs moisture. |
| DOT 5 | Silicone | 260°C (500°F) | Non-hydroscopic (doesn't absorb water), non-corrosive, not compatible with DOT 3/4/5.1. Produces a spongier pedal feel. |
| DOT 5.1 | Glycol | 260°C (500°F) | High-performance, higher boiling point than DOT 4, compatible with DOT 3/4. |
Always refer to your motorcycle's owner's manual for the correct brake fluid specification.
Preparation Steps
Proper preparation is key to a successful brake bleed.
- Park Your Motorcycle: Ensure your bike is on a level surface, ideally on a stand, to provide stability and easy access to the rear brake components.
- Access the Master Cylinder: Locate the rear brake master cylinder reservoir, typically near the rear brake pedal. Clean the area around the cap to prevent dirt from entering the system.
- Open the Reservoir: Carefully remove the reservoir cap and diaphragm.
- Remove Old Fluid (Optional): If the fluid looks very dirty, use a turkey baster or syringe to remove most of the old fluid from the reservoir, being careful not to let the reservoir run completely dry.
- Refill with New Fluid: Fill the reservoir with new, fresh brake fluid up to the "MAX" line. Keep the fluid container open and within reach for refilling during the process.
- Locate the Bleed Nipple: Find the bleed nipple on the rear brake caliper. Clean any dirt or debris from around it.
Step-by-Step Manual Rear Brake Bleeding Process
Follow these steps carefully to effectively purge air from your rear brake system.
- Attach the Tubing: Fit one end of the clear plastic tubing snugly over the bleed nipple on the rear brake caliper.
- Submerge the Other End: Place the other end of the tubing into your clear collection container, ensuring it is submerged in a small amount of new brake fluid. This prevents air from being drawn back into the system.
- Initiate the Bleeding Cycle:
- Press the Rear Brake Pedal: Firmly and steadily press the rear brake pedal down. You should feel resistance.
- Open the Bleed Nipple: While keeping the pedal depressed, use your wrench to open the bleed nipple a quarter to a half turn. You will see fluid and potentially air bubbles flow into the clear tubing. The brake pedal will likely sink further.
- Close the Bleed Nipple: Crucially, close the bleed nipple tightly before releasing the rear brake pedal. This prevents air from being sucked back into the system.
- Release the Brake Pedal: Once the nipple is closed, you can release the brake pedal. Allow it to return to its original position.
- Repeat the Process: Continue to repeat steps 3-4 (press pedal, open nipple, close nipple, release pedal) as many times as necessary.
- Monitor Fluid Level: Constantly check the fluid level in the master cylinder reservoir. Do not let it drop below the "MIN" mark to avoid drawing air into the system. Refill with fresh fluid as needed.
- Observe Fluid and Bubbles: Watch the fluid flowing through the clear tubing. You are looking for a steady stream of fluid with no air bubbles.
- Achieve Bubble-Free Flow: Continue the process until the fluid flowing out of the bleed nipple is completely clear of air bubbles, and the brake pedal feels firm and consistent.
- Final Steps:
- Tighten Bleed Nipple: Once all air is purged, ensure the bleed nipple is securely tightened (refer to your service manual for torque specifications, but typically snug is sufficient for hand tools).
- Remove Tubing: Remove the clear plastic tubing.
- Clean Up: Thoroughly clean any spilled brake fluid from the caliper, wheel, and swingarm using water or a dedicated brake cleaner.
- Top Off Reservoir: Fill the master cylinder reservoir to the "MAX" line with new brake fluid. Reinstall the diaphragm and cap securely.
- Test Brakes: Gently pump the rear brake pedal a few times to ensure it feels firm. Take your motorcycle for a slow, cautious test ride in a safe area to confirm proper brake function before riding at speed.
Troubleshooting and Tips
- Spongy Pedal Persists: If the pedal remains spongy, there might still be air in the system, or the master cylinder or caliper might have an internal issue. Re-bleed carefully, or consider further inspection.
- Bleed from Farthest to Closest (for multi-caliper systems): While the rear brake typically has one caliper, if your bike has dual rear calipers (rare but possible), always bleed the caliper furthest from the master cylinder first.
- Don't Rush: Take your time. Rushing can lead to mistakes and more air in the system.
- Cleanliness: Brake fluid is corrosive and attracts moisture. Keep everything clean and dry.
- Proper Disposal: Dispose of old brake fluid responsibly at an authorized recycling center.
By following these manual bleeding steps, you can restore your motorcycle's rear brake performance, ensuring a safer and more enjoyable ride. Regular brake maintenance is a critical aspect of motorcycle safety. For more detailed instructions specific to your model, always consult your motorcycle's service manual.
