au wagon brake shuddering under brakes

[HARMFUL 81]

Hi there everyone.
I have an au wagon on which about 6 months ago i replaced the front rotors and pads (slotted with bendix pads) due to warped standard discs. However it has developed shuddering again. Is this likely to be the discs again this early? is there any other likely problems - bearings/wheel balancing? The shuddering only happens when braking, although if the brakes are applied harder, their is no pulsating. Hope this all makes sense.