Need to replace some html code

Hello everyone.

I need some help with a problem because I have tried all the solutions I could think of and nothing seems to work.

What I need is a plugin/filter which replaces lines like these:
<td width="1" height="24" valign="top"> </td>
with:
<td width="1" height="24" valign="top"></td>
removing the space between the tags.

I have coded the following PHP code, but it simply doesn’t work.

<?php
/*
Plugin Name: MyFilter
*/

function my_filter($text)
{
$text = str_replace('> </td>', '></td>', $text);
return $text;
}

add_filter('the_content', 'my_filter');
?>

I have tried with a simpel “substr_count” call, but that can neather find any linies in the content provided by WordPress – and I know it’s there, because I can see it in the source in my browser.

I have tried to copy the HTML code from the WordPress page created with the visuel editor into a stand-a-lone PHP file and used the above function, which works as it should.

I hope that somebody can see the error and help me with a solution.

In advance, thanks

Best regards
Morten Johansen