jqGrid: POST data to server to fetch row data (filtering and searching)

I have a form like this:

<form id='myForm'>
<input type='text' name='search' />
<input type='text' name='maxPrice' />
</form>

and table for my jqGrid:

<table id='myGrid'></table>

I need to POST (not GET) the data from myForm to my server method in order to fetch the row data and populate the grid. So far, I've not been able to get jqGrid to POST anything. I double-checked my data serialization and it is serializing my form data properly. Here is my jqGrid code:

$("#myGrid").jqGrid({
    url: '/Products/Search") %>',
    postData: $("#myForm").serialize(),
    datatype: "json",
    mtype: 'POST',
    colNames: ['Product Name', 'Price', 'Weight'],
    colModel: [
        { name: 'ProductName', index: 'ProductName', width: 100, align: 'left' },
        { name: 'Price', index: 'Price', width: 50, align: 'left' },
        { name: 'Weight', index: 'Weight', width: 50, align: 'left' }
    ],
    rowNum: 20,
    rowList: [10, 20, 30],
    imgpath: gridimgpath,
    height: 'auto',
    width: '700',
    //pager: $('#pager'),
    sortname: 'ProductName',
    viewrecords: true,
    sortorder: "desc",
    caption: "Products",
    ajaxGridOptions: { contentType: "application/json" },
    headertitles: true,
    sortable: true,
    jsonReader: {
        repeatitems: false,
        root: function(obj) { return obj.Items; },
        page: function(obj) { return obj.CurrentPage; },
        total: function(obj) { return obj.TotalPages; },
        records: function(obj) { return obj.ItemCount; },
        id: "ProductId"
    }
});

Can you see what I'm doing wrong or should be doing differently?