The way I would approach this is to give all the links that open a slider a class, say "open", I would give them all a data-slider property, something like this:
<a href="#" class="open" data-slider="2">Open Slider</a>
You jquery function can then become generic:
$( ".open" ).click(function () {
var sliderNumber = $(this).data("slider");
if ( $( "#sliderbox" + sliderNUmber ).is( ":hidden" ) ) {
$( "#sliderbox" + sliderNUmber ).slideDown( "slow" );
$( ".arrow" + sliderNUmber).delay(300).fadeIn(500);
$(".balken" + sliderNUmber).delay(500).fadeIn(500);
$( "#sliderbox" ).slideUp( "slow" );
$( ".arrow" ).fadeOut(100);
$( ".balken" ).fadeOut(100);
var y = $(window).scrollTop(); //your current y position on the page
$('html, body').animate({
scrollTop: y+150
},500);
} else {
$( "#sliderbox" + sliderNUmber ).slideUp( "slow" );
$( ".arrow" + sliderNUmber ).fadeOut(100);
$( ".balken" + sliderNUmber ).fadeOut(100);
}
});
Now your slider function is more generic, and you can re-use it as many times as you want, just have to make sure you add the data-slider number to each link and make sure the sliding elements have the right IDs
Hope this helps.