Shimano HDB Low Power Troubleshooting
Troubleshooting hydraulic disc brakes with a lack of braking power
Troubleshooting hydraulic disc brakes with a lack of braking power
Diagnosing and Correcting Lack of Braking Power
A lack of braking power is one of the most common problems associated with disc brakes. It is often seen in conjunction with
soft lever feel and/or brake system noise. This guide will focus on diagnosing and correcting a lack of power, but it may prove
helpful to consult other Hydraulic Disc Brake Troubleshooting Guides.
PROPER PROTECTIVE EQUIPMENT, INCLUDING GLOVES AND SAFETY GLASSES,
SHOULD BE USED WHEN SERVICING HYDRAULIC DISC BRAKE SYSTEMS
First Things First
The first step is to define the problem. Before beginning any troubleshooting procedures, have a discussion with the rider to make
sure you fully understand the symptoms and their expectations. Next, make sure that the brake system itself is all in good order,
meaning:
• All components (lever, connectors, hose, caliper, pads, and rotors) are compatible with each other, installed properly, and
in good condition – refer to si.shimano.com for individual specifications
• The brake system is compatible with the bicycle frame and wheels
• The brake system is a good match for the rider’s intended usage
• Pads and rotors are not worn past the point of replacement
Problems and Solutions
In a system that is properly selected and installed, the two main culprits of a lack of braking power are insufficient pressure
or insufficient friction. A lack of pressure can be caused by anything from the lever down to the caliper, and is commonly
accompanied by problems with lever feel. Insufficient friction is generally centralized around the caliper/pad/rotor area and
often results in brake noise.
Insufficient Pressure
A lack of pressure is almost always caused by either a leak of some sort, or the presence of air/water in the system. Do a
thorough inspection of the brake system from lever to caliper, looking for signs of leaking mineral oil. Perform a pressure test
as described in the stand alone “Hydraulic Disc Brake Pressure Test” guide. Inspect the hose carefully for any kinks, crimps,
bulges, or other damage and replace if any are present. Replace any leaking components and re-bleed the system. If there are
no signs of leakage and a bleed fails to address the problem, replace the compression fittings and inserts on the hose.
Insufficient Friction
Lack of friction occurs because the pad-rotor interface has been compromised. A pad that is significantly darker than a
new pad suggests contamination of the surface, while a pad that is shiny suggests overheating – it IS possible to find both
problems on one brake. Examine the braking track. Black, gray, or brown discoloration can indicate contamination, while a rotor
showing yellow, brown, purple, or blue discoloration and/or warping has likely suffered heat damage. Replace any damaged
components. If heat damage is indicated, consider heat management options when selecting replacements. If contamination
is indicated, locate the source of contamination and take steps to prevent repeated contamination. Likely sources are a leaking
caliper, accidental exposure to bicycle lubricants, or environmental exposures.
A lack of braking power is one of the most common problems associated with disc brakes. It is often seen in conjunction with
soft lever feel and/or brake system noise. This guide will focus on diagnosing and correcting a lack of power, but it may prove
helpful to consult other Hydraulic Disc Brake Troubleshooting Guides.
PROPER PROTECTIVE EQUIPMENT, INCLUDING GLOVES AND SAFETY GLASSES,
SHOULD BE USED WHEN SERVICING HYDRAULIC DISC BRAKE SYSTEMS
First Things First
The first step is to define the problem. Before beginning any troubleshooting procedures, have a discussion with the rider to make
sure you fully understand the symptoms and their expectations. Next, make sure that the brake system itself is all in good order,
meaning:
• All components (lever, connectors, hose, caliper, pads, and rotors) are compatible with each other, installed properly, and
in good condition – refer to si.shimano.com for individual specifications
• The brake system is compatible with the bicycle frame and wheels
• The brake system is a good match for the rider’s intended usage
• Pads and rotors are not worn past the point of replacement
Problems and Solutions
In a system that is properly selected and installed, the two main culprits of a lack of braking power are insufficient pressure
or insufficient friction. A lack of pressure can be caused by anything from the lever down to the caliper, and is commonly
accompanied by problems with lever feel. Insufficient friction is generally centralized around the caliper/pad/rotor area and
often results in brake noise.
Insufficient Pressure
A lack of pressure is almost always caused by either a leak of some sort, or the presence of air/water in the system. Do a
thorough inspection of the brake system from lever to caliper, looking for signs of leaking mineral oil. Perform a pressure test
as described in the stand alone “Hydraulic Disc Brake Pressure Test” guide. Inspect the hose carefully for any kinks, crimps,
bulges, or other damage and replace if any are present. Replace any leaking components and re-bleed the system. If there are
no signs of leakage and a bleed fails to address the problem, replace the compression fittings and inserts on the hose.
Insufficient Friction
Lack of friction occurs because the pad-rotor interface has been compromised. A pad that is significantly darker than a
new pad suggests contamination of the surface, while a pad that is shiny suggests overheating – it IS possible to find both
problems on one brake. Examine the braking track. Black, gray, or brown discoloration can indicate contamination, while a rotor
showing yellow, brown, purple, or blue discoloration and/or warping has likely suffered heat damage. Replace any damaged
components. If heat damage is indicated, consider heat management options when selecting replacements. If contamination
is indicated, locate the source of contamination and take steps to prevent repeated contamination. Likely sources are a leaking
caliper, accidental exposure to bicycle lubricants, or environmental exposures.
