Vehicle issue js

$(".vehicle-data").hide();
    var activeVehicleData = $(".vehicle-nav .active a").attr("href");
    $(activeVehicleData).show();

    $('.vehicle-nav-scroll').click(function () {
        var topPos = 0;
        var direction = $(this).data('direction');
        var scrollHeight = $('.vehicle-nav li').height() + 1;
        var navHeight = $('#vehicle-nav-container').height() + 1;
        var actTopPos = $(".vehicle-nav").position().top;
        var navChildHeight = $('#vehicle-nav-container').find('.vehicle-nav').height();
        var x = -(navChildHeight - navHeight);



        // Scroll Down
       if ((direction == 'down') && (actTopPos > x) && (-navHeight <= (actTopPos - (scrollHeight * 2)))) {
            topPos = actTopPos - scrollHeight;
            $(".vehicle-nav").css('top', topPos);
            //alert(topPos+' '+ navChildHeight+' '+ x);
        }

        // Scroll Up
        if (direction == 'up' && 0 > actTopPos) {
            topPos = actTopPos + scrollHeight;
            $(".vehicle-nav").css('top', topPos);
        }
        return false;
    });