have you checked that load sensing valve is working-arm on valve should move when brake pedal pressed,also may need adjusting so its getting more brake pressure to rear.did you adjust rear brakes correctly [before cables connected to actuator,also are cables fitted to correct sides] is yoke on actuator free to swivel,make sure they aren't over adjusted ,you may need to bed new shoes in by applying handbrake whilst vehicle in motion [but take care doing this you need a very quiet road to do this!!]
k
October 2010