29/04/2017
Ensuring your motorcycle's braking system is in peak condition is not just about performance; it's fundamentally about your safety. Worn brake pads compromise stopping power, leading to dangerous situations on the road. Fortunately, replacing your rear brake pads is a manageable task for the keen DIY enthusiast, allowing you to save on garage fees whilst gaining invaluable knowledge about your bike. This comprehensive guide will walk you through the process of safely and effectively replacing the rear brake pads on your motorcycle's caliper, ensuring you can ride with confidence.
Before you begin, gather all necessary tools and materials. You'll need new brake pads (ensure they are the correct type for your motorcycle's make and model), a putty knife with a stiff blade, appropriate wrenches (including a torque wrench for precise tightening), and the correct type of hydraulic brake fluid as specified in your owner's manual. Always work in a well-lit area and on a stable surface.
Understanding Your Brake System
Your motorcycle's braking system relies on hydraulic pressure to force pistons within the caliper against the brake pads, which then clamp down on the brake disc to create friction and slow your wheel. Over time, the friction material on the pads wears down, necessitating replacement. Recognising the signs of wear, such as a squealing noise, reduced braking effectiveness, or a spongy brake pedal, is crucial for timely maintenance.
Pre-Installation Preparations and Safety Warnings
Before touching any components, remember that brake fluid is corrosive and can damage paintwork. Have rags ready to wipe up any spills immediately. Also, be mindful of the critical safety warnings associated with brake system maintenance.
Initial Steps
- Remove Saddlebag (If Applicable): If your motorcycle is equipped with a right saddlebag, remove it to gain unobstructed access to the rear brake caliper.
- Address Master Cylinder Fluid Level: Remove the rear master cylinder reservoir cap. As you push the brake caliper pistons back into their bores, the fluid level in the reservoir will rise. It's common for the fluid level to rise more than 1/8 inch (0.32 mm). You may need to remove some brake fluid from the reservoir to prevent overflow. Use a clean syringe or turkey baster for this, and dispose of the fluid responsibly.
Crucial Safety Warnings
WARNING: After servicing brakes and before moving your motorcycle, it is absolutely essential to pump the brakes to build brake system pressure. Insufficient pressure will severely affect brake performance, which could lead to a loss of control, resulting in serious injury or death.
WARNING: After repairing the brake system, always test the brakes at low speed in a safe, open area. If the brakes are not operating properly, testing at high speeds can lead to a dangerous loss of control, which could result in severe injury or death.
Step-by-Step Rear Brake Pad Replacement
This process focuses on the rear brake caliper, which typically uses two pad pins to retain the brake pads.
1. Loosening Pad Retaining Pins
Locate the two pad pins on your rear brake caliper. These are typically 12-point fasteners. Loosen, but do not remove, both pad pins. It's important to understand that there are often three bolts on the caliper body itself, but you must NOT remove any of these three bolts, as doing so could damage an internal O-ring, leading to major brake system issues.
2. Retracting the Inside Piston and Pad Removal
Using a putty knife with a stiff blade, carefully pry the inside brake pad back. Insert the knife between the pad and the brake disc, applying steady pressure. The goal is to push the caliper pistons back into their bores. Be extremely careful to prevent scoring or damaging the brake disc during this process. Once the pistons for the inside pad have been fully retracted, pull the loosened pad pins until the inside pad drops free. It is critical at this stage that you do not completely pull the pad pins from the caliper; doing so will make reassembly much more difficult.
As you remove the old pad, take note of its original orientation. This is vital for installing the new pad correctly. For many motorcycles, including some Harley-Davidson Softail models, the front left, front right (if present), and rear brake calipers use the exact same brake pad set. On the right side of the vehicle, the brake pad with two tabs on its backing plate typically installs on the inboard side of the caliper. On the left side of the vehicle (though this article focuses on the rear, the principle applies to universal pads), the pad with two tabs installs on the outboard side of the caliper. The curved portion of the pad must always face the rear of the motorcycle. For Softail rear brakes, this means the curved portion faces upwards.
3. Installing the New Inside Pad
Carefully install the new inside brake pad, ensuring it matches the original orientation of the pad you just removed. Pay close attention to the curved portion of the pad and any tabs on the backing plate. Once the pad is correctly seated, install the pad pins back through the new pad. Push them until you hear or feel an audible click, indicating they have snapped into place. Do not fully tighten them at this stage.
4. Retracting the Outside Piston and Pad Removal
Now, repeat the prying process for the outside brake pad. Pry between the pad and the brake disc to push the remaining caliper pistons back into their bores. While doing this, take a moment to inspect the pad pins you previously loosened. Check them for any signs of wear or grooving. If the wear on either pin exceeds 0.015 inch (0.38 mm), you must replace both pins to ensure proper brake operation and safety.
Once the outside pistons are fully retracted, completely remove both pad pins to free the outside brake pad. Again, note its original position and orientation for correct reinstallation.
5. Installing the New Outside Pad
Install the new outside brake pad, ensuring its orientation matches the pad you just removed. The curved portion of the pad must face the rear of the motorcycle. Once the pad is in place, reinsert both pad pins through the holes in both the inner and outer brake pads. Once fully inserted, tighten both pad pins to the specified torque setting.
| Component | Torque Specification |
|---|---|
| Pad Pins | 20.3–22.6 N·m (180–200 in-lbs) |
6. Final System Checks and Adjustments
- Pump the Brake Pedal: This is a critical step. Repeatedly pump the brake pedal until the pistons move out and firmly contact both new brake pads. You should feel the brake pedal firm up. Verify that the pistons are correctly located against the pads.
- Check Brake Fluid Level: Re-check the brake fluid level in the master cylinder reservoir. Fill it to approximately 1/8 inch (3 mm) below the top of the cylinder if necessary. It is paramount that you do not overfill the master cylinder, as this can create excessive pressure within the system, potentially damaging components. Always use the correct D.O.T. hydraulic brake fluid type as specified in your motorcycle's owner's manual. Using the wrong fluid can cause catastrophic brake failure.
- Install Master Cylinder Cap: Reinstall the master cylinder reservoir cap. Tighten the reservoir cap screws to the specified torque.
| Component | Torque Specification |
|---|---|
| Reservoir Cap Screws | 0.7–0.9 N·m (6–8 in-lbs) |
Post-Replacement Testing
After completing the brake pad replacement and ensuring all components are properly torqued and the brake system is bled (if necessary, though typically not for just pad replacement if care is taken not to introduce air), it is imperative to test your brakes. Start by testing at very low speeds in a safe, open area, such as a deserted car park. Gradually increase speed and test the brakes, ensuring they feel firm and responsive before venturing onto public roads. Listen for any unusual noises and check for any fluid leaks.
Common Mistakes to Avoid
- Forgetting to Pump Brakes: This is the most dangerous oversight. Without pumping, the brake pedal will go straight to the floor, leaving you with no braking power.
- Using Incorrect Brake Fluid: Always refer to your owner's manual. Mixing fluid types or using the wrong DOT rating can damage seals and lead to brake failure.
- Damaging Caliper O-rings: Attempting to remove the three main caliper bolts can cause internal O-ring damage, leading to leaks and requiring a full caliper rebuild.
- Scoring the Brake Disc: Being too aggressive with the putty knife can scratch the disc, leading to uneven pad wear and compromised braking.
- Incorrect Pad Orientation: Installing pads backwards or with incorrect tab alignment can lead to uneven wear, noise, and reduced braking effectiveness.
- Overfilling Master Cylinder: This can cause fluid to leak, damage paint, or create excessive pressure within the system, potentially seizing the brakes when they heat up.
Frequently Asked Questions (FAQs)
How often should I replace my motorcycle brake pads?
Brake pad life varies significantly based on riding style, conditions, and pad material. Generally, it's good practice to inspect them every 5,000 to 10,000 miles or at least once a year. Replace them if the friction material is less than 2mm thick, if you hear squealing, or if braking performance degrades.
What are the signs of worn brake pads?
Common signs include a squealing or grinding noise when braking, a spongy or soft brake pedal, increased stopping distances, or visible thinning of the pad material when inspecting the caliper.
Can I use any brake fluid in my motorcycle?
Absolutely not. Your motorcycle's brake system is designed for a specific DOT (Department of Transportation) fluid type, usually DOT 3, DOT 4, or DOT 5. Mixing incompatible fluids or using the wrong type can cause seals to swell or degrade, leading to brake failure. Always consult your owner's manual.
What happens if I don't pump the brakes after changing the pads?
If you don't pump the brakes, the pistons will not be extended to meet the new pads. The first time you press the brake pedal, it will go straight to the handlebar or footpeg with no braking effect, leading to a dangerous situation and potential accident.
Why is brake pad orientation important?
Brake pads are often designed with specific leading and trailing edges, or with tabs that align them correctly within the caliper. Incorrect orientation can lead to uneven wear, noise, reduced braking efficiency, and even premature failure of the pads or caliper components.
Conclusion
Replacing your motorcycle's rear brake pads is a fundamental maintenance task that directly impacts your safety on the road. By following these detailed steps and paying close attention to the critical warnings, you can confidently perform this service yourself. Remember, proper brake maintenance is non-negotiable for a safe and enjoyable riding experience. If you ever feel uncertain or encounter unexpected issues, do not hesitate to consult a qualified motorcycle mechanic.
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