If a master cylinder or piston shows any damage, replace them.

If a cup is worn, damaged softened (rotted), or swollen, the piston assembly should be replaced to renew the cups.
If fluid leakage is noted at the brake lever, the piston assembly should be replaced to renew the cups.
If they are damaged, replace them.
If the springs are damaged, replace them.
If the relief port becomes plugged, the brake pads will drag on the disc. Blow the ports clean with compressed air.
Front Master Cylinder [I] Rear Master Cylinder [J]

Rear Master Cylinder Installation
Brake DiscESD (Electronic Steering Damper) ECU Communication Error (Service Code 3C,
ZX1000JD/KD)
ESD ECU Communication Line Inspection
When the data (for status of ESD system) is not sent from
the ESD ECU to the meter unit and ECU, the service code
3C is displayed.
The data is sent through the CAN communication line.
The service code 3C is detected with the meter unit.
The FI symbol does ...
Tachometer
The tachometer shows the engine
speed in revolutions per minute (r/min,
rpm).
On the right side of the tachometer
face is a portion called the “red zone�.
Engine r/min (rpm) in the red zone is
above maximum recommended engine
speed and is also above the range for
good performance.
...
Throttle Grip and Cables
Free Play Inspection
Refer to the Throttle Control System Inspection in the Periodic
Maintenance chapter.
Free Play Adjustment
Refer to the Throttle Control System Inspection in the Periodic
Maintenance chapter.
Cable Installation
Install the throttle cables in accordance with the Cable,
...