ajax replaces inputs in form, then they don't get passed through post

ajax replaces inputs in form, then they don't get passed through post

Ok, so I have just recently started using ajax and I love it but I am having some issues with mixing ajax and good old fashioned submitting  of forms. I have a page that has a form on it containing a bunch of different inputs. Some of these inputs depend on others so I set them up with .change for a select and .click for a button to refresh some date information. I am using Code Igniter so I send the ajax to a controller that returns a view which is essentially just a section of my page. If I use ajax to update any of these field, then the input I updated with ajax doesn't get passed through post on the submit of the form. Is there something more I need to do after I replace these inputs to "add" them back into the form or something of that sort? Thank you again for your help. (btw, I am not sure if this is the proper place to ask for help, if it is not, please delete and give me direction as to where I should ask, thanks!)

Code:
this is the ajax call:

                $(document).ready(function() {
                    $('#change_button')
                        .livequery('click', function() {
                        
                            var form_data = {
                                    pickup_date: $('#pickup_date').val(),
                                    pickup_hour: $('#pickup_hour').val(),
                                    pickup_minutes: $('#pickup_minutes').val(),
                                    dropoff_date: $('#dropoff_date').val(),
                                    dropoff_hour: $('#dropoff_hour').val(),
                                    dropoff_minutes: $('#dropoff_minutes').val(),
                                    type_of_cart: $('#cart_dropdown').val(),
                                    ajax: '1'
                            };
                            
                            $.ajax({
                                    url: "<?php echo site_url('reservations/ajax_change'); ?>",
                                    dataType: 'html',
                                    type: 'POST',
                                    data: form_data,
                                    success: function(msg) {
                                            $('#cart_types').html(msg);
                                    }
                            });

                            return false;
                    });

#cart_types deals with a table that has info about different carts:
From the view that is returned as msg:
        <div class="cart_types" <?php if(!empty($length_error['dates'])) {echo 'style="display: none"';} ?> id="cart_types">
            <h4>Please select a type of cart - UPDATED!</h4>
            <table>
                <tr>
                    <td style="text-align: center;font-weight: bold;">
                        Type of Cart
                    </td>
                    <td style="text-align: center;font-weight: bold;">
                        Picture
                    </td>
                    <td style="text-align: center;font-weight: bold;width: 35%;">
                        Description
                    </td>
                    <td style="text-align: center;font-weight: bold;">
                        Price
                    </td>
                </tr>
                <tr>
                    <td><div class="cart_dropdown">
                        <?php echo form_dropdown('types', $available_cart_types, $types, 'id="cart_dropdown"'); ?>
                        </div>
                    </td>
                    <td>
                        <img src="<?php echo base_url() . $type_info['picture_url']; ?>" width="216" height="144" />
                    </td>
                    <td>
                        <?php echo $type_info['description']; ?>
                    </td>
                    <td style="text-align: center;font-weight: bold;">
                        $<?php echo $type_info['price']; ?>
                    </td>
                </tr>
            </table>

        </div>