Shimano HDB Slow Return
Diagnosing and correcting a slow lever return with hydraulic disc brakes
Diagnosing and correcting a slow lever return with hydraulic disc brakes
Diagnosing and Correcting Slow Lever Return and “Pump Up”
This troubleshooting guide will focus on two related problems with disc brake systems: slow lever return and “pump up” – the
feeling that the first brake pull is normal while subsequent pulls have less travel. These are often two sides of the same coin,
which is why they are being addressed simultaneously.
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
There are two categories of problems that cause slow lever return or pump up: mechanical and hydraulic. A mechanical
problem is anything outside of the hydraulic system that is acting to restrict movement. These are more common in cases
where the symptom is described as “slow return”. Hydraulic problems occur within the closed hydraulic system and pertain
to the function of the mineral oil. These are more common in cases where the emphasis is on the feel of “pump up”.
Contaminated Mineral Oil
An overtightened clamp can cause the master cylinder to distort. Loosen the clamp slightly and check for improvement.
On some levers, such as the ST-R8070 or ST-R9170, the push rod attached to plunger may need to be lubricated using
SHIMANO Premium Grease. At the caliper, verify the pistons move smoothly – if necessary, perform a service as outlined in the
“Hydraulic Disc Brake - Caliper Service” guide. If the problem persists, gently move the lever through its travel while paying
close attention to the feel. If it feels gritty or gummy, there is a good chance the master cylinder had been compromised and
the lever should be replaced.
Leaking System
The most common hydraulic problem is an obstruction in the line that impedes the free movement of hydraulic fluid. Possible
obstructions include thread preparation material, plastic J-kit cover remnants, or brake dust and road grime. The most likely
place for this to happen is at the inserts at the transition points between hose and lever or hose and caliper. If mechanical
possibilities have been eliminated, the system can often be corrected by replacing the inserts and cleaning out the hose.
Attach a hose to the caliper bleed port, then open and allow the system to fully drain. Uninstall the hose, discard the used
compression fittings, cut off the old inserts and blow compressed air through the hose to help remove contaminants. On
bicycles with a banjo fitting, you can also remove the bolt to clean the bolt and fitting. If this does not resolve the issue, the
obstruction is inside of the lever or caliper. Obstructions in these locations are difficult to remove, and there is a high likelihood
the component in question will need to be replaced.
The other hydraulic issue you may face is contamination of the mineral oil. If the symptoms exist only when the system is hot,
there is a chance that there is either air or water in the line. Presence of either will move the contact point of the lever further
out. Air will feel extremely spongy and soft, while water can feel soft or firm depending upon the level of contamination and
the heat of the system. Drain the oil and bleed the system, making sure all the contaminated oil is purged through the caliper
end. Follow the instructions in the appropriate Dealer Manual, found at si.shimano.com.
This troubleshooting guide will focus on two related problems with disc brake systems: slow lever return and “pump up” – the
feeling that the first brake pull is normal while subsequent pulls have less travel. These are often two sides of the same coin,
which is why they are being addressed simultaneously.
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
There are two categories of problems that cause slow lever return or pump up: mechanical and hydraulic. A mechanical
problem is anything outside of the hydraulic system that is acting to restrict movement. These are more common in cases
where the symptom is described as “slow return”. Hydraulic problems occur within the closed hydraulic system and pertain
to the function of the mineral oil. These are more common in cases where the emphasis is on the feel of “pump up”.
Contaminated Mineral Oil
An overtightened clamp can cause the master cylinder to distort. Loosen the clamp slightly and check for improvement.
On some levers, such as the ST-R8070 or ST-R9170, the push rod attached to plunger may need to be lubricated using
SHIMANO Premium Grease. At the caliper, verify the pistons move smoothly – if necessary, perform a service as outlined in the
“Hydraulic Disc Brake - Caliper Service” guide. If the problem persists, gently move the lever through its travel while paying
close attention to the feel. If it feels gritty or gummy, there is a good chance the master cylinder had been compromised and
the lever should be replaced.
Leaking System
The most common hydraulic problem is an obstruction in the line that impedes the free movement of hydraulic fluid. Possible
obstructions include thread preparation material, plastic J-kit cover remnants, or brake dust and road grime. The most likely
place for this to happen is at the inserts at the transition points between hose and lever or hose and caliper. If mechanical
possibilities have been eliminated, the system can often be corrected by replacing the inserts and cleaning out the hose.
Attach a hose to the caliper bleed port, then open and allow the system to fully drain. Uninstall the hose, discard the used
compression fittings, cut off the old inserts and blow compressed air through the hose to help remove contaminants. On
bicycles with a banjo fitting, you can also remove the bolt to clean the bolt and fitting. If this does not resolve the issue, the
obstruction is inside of the lever or caliper. Obstructions in these locations are difficult to remove, and there is a high likelihood
the component in question will need to be replaced.
The other hydraulic issue you may face is contamination of the mineral oil. If the symptoms exist only when the system is hot,
there is a chance that there is either air or water in the line. Presence of either will move the contact point of the lever further
out. Air will feel extremely spongy and soft, while water can feel soft or firm depending upon the level of contamination and
the heat of the system. Drain the oil and bleed the system, making sure all the contaminated oil is purged through the caliper
end. Follow the instructions in the appropriate Dealer Manual, found at si.shimano.com.
