I have replaced my back drums and pads on my 08 impreza when brakinging im getting a shaking from the rear drums i used napa parts and im puzzled as to why im getting such a bad vibration from the rear end only occurs when braking. shaking is tipical of a warped drum so im puzzled becouse everything is new and im still having a issue any suggestions. tires and rims are ballaced

theram,

 

Obviously something about the brake work you did was not correct. Either the drums are out of round, or the brake shoes' arch is incorrect and the shoes aren't contacting the drum for their total length. You may even find that the shoes springs are incorrectly installed, or the short springs that fasten the shoes to the backing plate have popped off, allowing the show to twist sideways and jamb against the drum.

 

Regardless, you won't know until you pull the drums off and have a look. Good Luck!