ABS problems

[Smokie]

hi all every now and then, when braking, i get a judder through the pedal as if the ABS is kicking in. it doesn't happen all the time, and can happen under any type of braking i.e sometimes light braking in traffic or heavy braking. all of the discs and pads are in good condition and i don't get any warning lights on the dash when it does happen? any ideas or suggestions would be welcome.