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 DiscClutch Removal
Remove:
Clutch Cover (see Clutch Cover Removal)
Clutch Spring Bolts [A]
Clutch Springs (with Clutch Spring Holders)
Clutch Spring Plate [B]
Pusher [C]
Remove:
Friction Plates (10) [A]
Steel Plates (9) [B]
Spring [C]
Spring Seat [D]
Hold the sub clutch hub [A] ...
Starter Clutch Inspection
Remove:
Torque Limiter Cover (see Torque limiter Removal)
Turn the torque limiter [A] by hand. The torque limiter
should turn forward freely [B], but should not turn backward.
If the starter clutch does not operate as it should or if it
makes noise, go to the next step.
Disassem ...
ZX1000JB/KB Models
1. Run the fuse box 2 lead in front of the rib for the fuse box 2.
2. Seat Lock Cable
3. Hook the licence plate light lead and the left turn signal light lead on
the projection of the tool
kit case.
4. Rib for Fuse Box 2
5. Run the starter relay lead in back of the rib for the fuse box 2 ...