Servetta rear brake pulsing pedal

Hi all
I have a servetta sx200 lynx 84 with pulsing rear brake I have changed the rear hub several times and makes no difference checked layshaft for trueness and bearing is all ok, but still have the intermittent brake pedal as if the drum is oval. Any ideas thanks Dave
I have a servetta sx200 lynx 84 with pulsing rear brake I have changed the rear hub several times and makes no difference checked layshaft for trueness and bearing is all ok, but still have the intermittent brake pedal as if the drum is oval. Any ideas thanks Dave