Shimano HDB Soft Levers
Diagnosing a soft lever feel in hydraulic disc brakes
Diagnosing a soft lever feel in hydraulic disc brakes
Diagnosing and Correcting Soft Lever Feel
Soft lever feel is one of the most common problems associated with disc brakes. It is often seen in conjunction with a lack of
braking power and/or brake system noise. This guide will focus on diagnosing and correcting a soft lever feel, but it may prove
helpful to consult the other Hydraulic Disc Brake Troubleshooting Guides.
Procedure
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
A soft lever feel is most often caused either by a leak in the system or contamination of the mineral oil that operates the
system. A leak can occur anywhere in the system, but unless it is relatively large, there will only be a small change in braking
power. If leaking fluid contaminates pads or rotors, there may be significant noise during braking. Contaminated mineral oil
will almost always result in a significant loss of braking power.
Contaminated Mineral Oil
The most common contaminants of mineral oil are air and water. If the lever feel is extremely soft at all times, or if the lever
feels good most of the time but gets extremely soft after the bike is stored hanging from one wheel or upside down, then air
bubbles in the system are the likely culprit. If the system only suffers from a soft lever feel after extended braking, then water
is more likely. In either case, the system should be bled according to the appropriate Dealer Manual, found on si.shimano.
com. If there are repeated contamination problems or the mineral oil appears severely discolored, perform the same trouble
shooting process associated with locating a leak. Additionally, make certain that the pistons are regularly cleaned and
lubricated – see the standalone “Hydraulic Disc Brake – Caliper Service” guide.
Leaking System
Do a thorough inspection of the brake system from lever to caliper, looking for signs of leaking mineral oil or damage to the
hose. Pay special attention to the flange connecting bolt(s) and/or banjo fittings, as well as to the back side of the master
cylinder. Perform a pressure test as described in the “Hydraulic Disc Brake Pressure Test” guide. Replace any leaking
components. If the lever has a positive initial stop and then gradually pulls to the bar, replace the olives and inserts on the
hose. If the lever feels spongy and soft, if the lever has a very gradual stop, or if you can see any crimps, kinks, bulges, or other
deformations, replace the hose.
Soft lever feel is one of the most common problems associated with disc brakes. It is often seen in conjunction with a lack of
braking power and/or brake system noise. This guide will focus on diagnosing and correcting a soft lever feel, but it may prove
helpful to consult the other Hydraulic Disc Brake Troubleshooting Guides.
Procedure
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
A soft lever feel is most often caused either by a leak in the system or contamination of the mineral oil that operates the
system. A leak can occur anywhere in the system, but unless it is relatively large, there will only be a small change in braking
power. If leaking fluid contaminates pads or rotors, there may be significant noise during braking. Contaminated mineral oil
will almost always result in a significant loss of braking power.
Contaminated Mineral Oil
The most common contaminants of mineral oil are air and water. If the lever feel is extremely soft at all times, or if the lever
feels good most of the time but gets extremely soft after the bike is stored hanging from one wheel or upside down, then air
bubbles in the system are the likely culprit. If the system only suffers from a soft lever feel after extended braking, then water
is more likely. In either case, the system should be bled according to the appropriate Dealer Manual, found on si.shimano.
com. If there are repeated contamination problems or the mineral oil appears severely discolored, perform the same trouble
shooting process associated with locating a leak. Additionally, make certain that the pistons are regularly cleaned and
lubricated – see the standalone “Hydraulic Disc Brake – Caliper Service” guide.
Leaking System
Do a thorough inspection of the brake system from lever to caliper, looking for signs of leaking mineral oil or damage to the
hose. Pay special attention to the flange connecting bolt(s) and/or banjo fittings, as well as to the back side of the master
cylinder. Perform a pressure test as described in the “Hydraulic Disc Brake Pressure Test” guide. Replace any leaking
components. If the lever has a positive initial stop and then gradually pulls to the bar, replace the olives and inserts on the
hose. If the lever feels spongy and soft, if the lever has a very gradual stop, or if you can see any crimps, kinks, bulges, or other
deformations, replace the hose.
