One of the most important, and often neglected, components of a motorcycle is its brakes. When the brakes fail, a motorcycle is left with very few means to stop itself. Brake problems present themselves in many ways, often appearing in the form of a soft brake lever pull that prevents the brake from operating at its full potential. Locked or non-functional brakes can also develop, becoming major problems if left unchecked. Identifying these problems and pinpointing the cause can be done at home, but requires a basic understanding of how hydraulic brake systems operate.
Inspect the entire brake circuit for leaks or punctures that may cause a loss of hydraulic pressure. This includes the brake lines and all of the fittings on the caliper and master cylinder. Punctures and leaks can allow air and moisture to enter into the circuit, creating a loss in hydraulic pressure.
Pull in the brake lever. Does the lever feel firm or does it feel soft and mushy? A soft brake lever is a sign that air is trapped in the brake line, disrupting the hydraulic pressure between the brake caliper and the brake lever. Bleed the brake line at the caliper and remove any air bubbles to restore the hydraulic pressure in the brake system.
Remove the brake fluid reservoir cap and take a look at the brake fluid. Clean fluid is usually clear and light amber in colour. If the fluid is dark and cloudy, it has been contaminated by moisture build-up and will create a loss of hydraulic pressure in the line. Moisture can also create a slimy residue that could clog the brake master cylinder and the caliper pistons if not dealt with. Drain the fluid from the entire brake circuit and refill with fresh fluid before bleeding out any trapped air.
Remove the brake caliper from the rotor and take out the brake pads. Pump the brake lever repeatedly and observe the pistons as they extend and retract in the caliper. If the pistons do not retract, disassemble the caliper and clean out any obstructions that prevent the piston from moving properly. Frozen pistons are the main cause of brake lock-up.
Refer to a factory service manual specific to your motorcycle for detailed troubleshooting techniques and repair instructions. If you feel that you do not possess the skills necessary to properly diagnose your motorcycle's brake system, contact a qualified technician.
Do not ride your motorcycle if you suspect that there is a problem with the brakes. A brake failure can cause a catastrophic loss of control and may result in injury or death.