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 DiscOutline
When a problem occurs with DFI system, the warning indicator
light (LED) [A] and FI warning symbol [B] goes on
to alert the rider. In addition, the condition of the problem is
stored in the memory of the ECU. For models equipped with
an immobilizer system, the warning indicator light (LED)
and ...
ESD (Electronic Steering Damper) ECU Removal (ZX1000JD/KD)
NOTICE
Never drop the ECU especially on a hard surface.
Such a shock to the ECU can damage it.
Lift up the front portion of the fuel tank, and hold it with a
suitable bar or block (see Fuel Tank Removal in the Fuel
System (DFI) chapter).
NOTE
When removing the ESD ECU only, there ...
Sidestand Switch Operation Inspection
Raise the rear wheel off the ground with the stand (see
Rear Wheel Removal in the Wheels/Tires chapter).
Inspect the sidestand switch [A] operation accordance to
below table.
Sidestand Switch Operation
If the sidestand switch operation does not work, inspect
or replace the foll ...