abs!(O)(!)

hi there.ijust want to ask what is the normal freequency of the antilock operations during heavy braking on slippery ground.although the abs unit is ok(no warning lamps etc)and the system works fine,iget this feeling of fewer antilock pulses.sometimes for only milisconds the wheel(s)lock and then unlock again.obviously depends of the ground.could this be electrical problem?or asolenoid in the abs block?any ideas?surely somebody should be an expert on the bendix system to know what's happening.thank you very much.