The factory brakes on the A and early B model ZX-12R (2000-2002) are equipped with six piston Tokico calipers. Many people report that these calipers, while providing ample stopping power when working well, are finicky and prone to piston sticking, and are difficult to bleed well. On my ZX-12R the brakes worked well enough but required a lot of travel of the brake lever, to within 1/2″ of the handlebar, to achieve effective braking from a speed in excess of 70 mph. When the time has come to replace the pads I have decided to replace the calipers with a setup that is easier to maintain. The process for this was as follows:
- Remove the brake lines at the calipers, allow the fluid to drain into a container. Use rags under and near the calipers to catch any spilling brake fluid.
- Remove the calipers from the forks.
- Disassemble the calipers to inspect the cylinders, seals and pistons
- Clean all components
Re-assemble the calipers. I saved mine for now in case I prefer the OEM calipers, but if the replacement ones work well, the Tokicos may end up for sale. They turned out to be in perfect shape, no rust, deposits or damage of any sort. All seals were pliable and smooth, and were re-used.
The replacement calipers that people use come in a variety of options. Many people prefer to use a radial setup. The difference between the older axial setup and the newer radial setup is the positioning of the calipers with respect to the axis of the fork: on the axial setup, the mounting bolts are perpendicular to the plane of the fork and the braking force applies both twisting and bending forces to the fork leg. In a radial setup, the mounting bolts lie in the same plane as the fork leg, and the braking force applies a predominantly bending component to the fork.
I am not sure I see a practical difference for normal riding, plus retrofitting an axial forks with radial brackets does not really change the geometry of the mounts, therefore I decided to use a set of axial calipers. Readily available 4-piston Nissin calipers from 1987-91 GSX-R 1100 and 750, as well as from a 1200 Bandit have the same mounting pattern and are designed for the same 320 mm rotor, so I went with these.
The Nissins were obtained from E-bay, disassembled, thoroughly cleaned and re-assembled. They did not require seal replacement and now, two years later, did not show any sign of a leak. The Nissin calipers have piston area approximately the same as the factory Tokico calipers and therefore braking force applied to the disks has to be very close to that designed by the Kawasaki engineers. This is in contrast with some other setups people install, including the Yamaha R1 radial calipers: even though riders using those report no issues, the piston area and the resulting clamping force of those is lower than that of the 6-piston Tokico, and my reasoning was, this may be Ok for a lighter R1 but the ZX-12R is a heavier motorcycle and may need the clamping force of a larger piston area.
In the end the modification proved to be effective and simple, and my ZX-12R still has the 4-piston Nissin calipers in the front.