Why is my ZX-6R’s front end juddering under braking?
Q. When I brake at slow speed on my Kawasaki ZX-6R J2 track bike it feels as if the brakes are only working intermittently and at higher speeds the front shudders a lot.
The brake pads are new, the brake fluid is fine with no air and the Galfer discs have done around 4000 miles in the last four years.
Luciano, MCN forums
A. The discs could be warped as that would cause all the problems listed above, so you should check for disc run-out, but 4000 miles on a set of discs is nothing. Then again, play in the front wheel bearings could damage the discs, and if the wheel has been removed and left lying on the discs you could pick up some damage there.
The other areas to check are the caliper seals. When you put new pads in, their greater thickness pushes the pistons back into the caliper body and if the exposed parts of the pistons have become pitted they will snag on the caliper seals and keep the pad in light contact with the disc.
Take the pads out and pump the pistons out and inspect and clean. You may get away with taking the crud off them with brake cleaner. But if there is any damage to them then you will have to get them replaced.