How to Troubleshoot a Motorcycle's Front Brakeby Chris Gilliland
Your motorcycle's front brake is relied on heavily for nearly every braking maneuver found on the road or trail, making it a vital part of the machine's performance. When problems arise within the front brake circuit, your safety, as well as the motorcycle's ability to brake, are put at risk. Taking detailed notes of the symptoms, such as a mushy brake lever, abnormal noises or vibration, will help you to pinpoint the exact problem. These notes will also help a motorcycle technician determine the right repairs, should you not be able to troubleshoot your motorcycle's front brake yourself.
Symptom: Soft Brake Lever
Inspect the front brake hose and its fittings on the master cylinder, positioned on the right handlebar, and the front wheel's brake caliper. Look for obvious signs of damage, such as cracks or leaks that can allow air and dirt to enter the brake circuit. Replace the brake hose and fittings if they are damaged in any way.
Inspect the front brake master cylinder for leaks. Look specifically at the mating area around the brake fluid reservoir and at the piston below the brake lever. Replace the brake piston or fluid reservoir if there is any sign of leakage at either part.
Unscrew the front brake master cylinder's fluid reservoir, using a Phillips screwdriver. Lift the reservoir diaphragm out of the master cylinder and inspect the condition of the brake fluid. Drain and flush the brake circuit if the brake fluid is dark brown or is contaminated by debris.
Unbolt the brake caliper from the front fork, using a socket wrench. Pull the caliper off of the front brake disc. Inspect the exterior of the caliper for signs of leakage at the brake hose. Inspect the inner mount of the caliper for signs of leakage around the brake pad pistons. Replace the brake caliper if it is damaged in any way.
Flush the brake circuit. Fill the master cylinder's brake fluid reservoir with new brake fluid. Place a plastic tube over the bleed valve on the front brake caliper. Open the bleed valve, turning the valve counterclockwise a half of a turn with a wrench. Pull in the brake lever and hold it in place. Close the bleeder valve, turning the valve clockwise with a wrench. Release the brake lever slowly. Repeat until the fluid trapped in the plastic tube is clear and free of sediment or bubbles.
Symptom: Vibration or Noise
Unbolt the brake caliper from the front fork, using a socket wrench. Pull the caliper off of the front brake disc.
Inspect the caliper's brake pads, looking specifically for uneven material wear on both brake pads. Replace the brake pads and inspect the front brake disc if the pads are unevenly worn. Measure the remaining amount of pad material, using digital calipers, if the pads do not exhibit signs of uneven wear. Replace the brake pads if there is less than 1 mm of pad material remaining.
Inspect the inner and outer face of the front brake disc for scarring or signs of obvious damage. Replace the front brake disc if the damage is deep enough to catch your fingernail on.
Lift the front wheel off of the ground, using a motorcycle stand. Rotate the front wheel slowly and observe the front brake disc for signs or warping or distortion. Replace the front brake disc if it is warped or distorted in any way.
- Vibrations at the front wheel may also be attributed to problems within the front fork or wheel. Have the motorcycle inspected by a qualified motorcycle technician if problems persist after troubleshooting the front brake circuit.
- Refer to a factory service manual for additional troubleshooting techniques specific to your motorcycle.
- Do not attempt this task if you are not familiar with brake disassembly or bleeding techniques. Instead, seek the help of a trained motorcycle technician.
Items you will need
- Phillips screwdriver
- Socket wrench
- Brake hose and fittings
- Brake piston
- Front brake master cylinder fluid reservoir
- Front brake caliper
- Brake fluid
- Plastic tubing
- Wrench set
- Brake pads
- Motorcycle stand
- Front brake disc
- "The Professional Motorcycle Repair Program"; Professional Career Development Institute; 1995
- "Kawasaki ZX-6R Motorcycle Service Manual"; Kawasaki Heavy Industries; 2004
- "Honda CBR600RR Service Manual"; Honda Motor Co.; 2005
- Dan's Motorcycle: Hydraulic Brakes and Clutch
- manette des gaz 2 image by Jerome Dancette from Fotolia.com