squeaky brakes

My bus is still of the road awaiting engine but seem to remember that it had horendous squeaky front brakes on braking that I could not cure. It has standard brakes all round. I tried new pads. I fitted shims behind the pads. and I copper greased everthing And they still squeaked. Any ideas.

78 bay my disc are 1yr. old with pads but when driven for a while they squeak when you apply gently,does copper grease dry out after a while as this is what was on backs of them. or should i just replace pads and if so what make are best ,cheers