Can't change grip by script?

I tried to change GripForward, GripRight, GripPos and GripUp by script. It didin't work ! NOTHING HAPPENED! Can someone help? script:

function onButton1Down(mouse)
        sp.GripForward = Vector3.new(-0.342, -0.735, -0.586)
        sp.GripPos = Vector3.new(0, -0.6, 0.5)
        sp.GripRight = Vector3.new(0.938, -0.234, -0.254)
        sp.GripUp = Vector3.new(-0.049, 0.637, -0.77)
        sp.Grip = CFrame.new()
end