passing select value to php variable

passing select value to php variable

I am at an impass.
 
I want to pass the value of the selected drop down menu selected option. To a php variable that will be used in a MySQL statement, which in turn will alter a second drop down menu. Here is what happens. When I make my selection from the first drop down menu nothing changes on the second drop down menu. After I clicked the submit button then the change takes place. What do I need to do to make the change take place with out having to click the submit button? Thanks for any help, since I am stuck.
 
  1. <script type="text/javascript">
      $(document).ready(
       function(){
       $('#selFaxType').click(function() {
        //var selFaxTypeID = $('#selFaxType option:selected').val();
        var selFaxTypeID = $('#selFaxType').val();
        $("input[name=selFTID]").val(selFaxTypeID);
        $.post("fax_details.php", {selFTID: selFaxTypeID}, function(data){});
       });
       $('.datepicker').datepicker();
       }
      );
     </script>











  3. //Get value from POST 
    <?
    $selFTID = CleanNumber($_POST['selFTID']);

  5. //MySQL statement
    <select name="selFaxSubType" id="selFaxSubType" size=1>
    <option value=""></option>

  6. <?php
    echo "selFTID: $selFTID <br />";
    $strSQL = 'SELECT fax_sub_type_id, fax_sub_type FROM fax_sub_types WHERE fax_type_id ="'. $selFTID . '" AND fax_sub_type_disable=0 ORDER by fax_sub_type';

  8. //Store value in a hidden field
    <input name="selFTID" id="selFTID" type="hidden" value="<?=$selFTID?>" />