knocking when braking

[AKFM1]

hey people, im getting a knockin sound when im pressing the brake pedal. sounds like its coming from the rear of the car but dont know where to start looking. anyone else had this problem? can anyone point me in direction of where to start looking for problem. thanks in advance

 

[BRUCEY]

mine started doing this recently too, found the problem, a dirty great crack all way across the disc, have a look

 

[AKFM1]

thanks i will have a check today. but i recently changed the rear discs and pads so i hope it aint that!! anymore suggestions??:S

 

[AKFM1]

anyone???

 

[AKFM1]

checked the discs and look fine. anyone know what may cause the knocking/thumping noise when i brake??:S