Breaking up a navigation menu
From a once over:


You could have used a loop instead of .each(), it would be marginally faster
Your indenting is off, I assume you had trouble pasting the code
.9 and .7 are magic constants, you should declare these with var and a good name
I would use a ternary for this:

if {
    var newWidth= ;
    $('#navUl').css({"maxWidth":newWidth});
} else {
    $('#navUl').css({"maxWidth":});
}


could be

var navWidth = ( menuLength &gt; windowWidth *.9 ) ? menuLength *.7 : windowWidth;
$('#navUl').css({"maxWidth":navWidth});


of course with properly named constants this might stretch too much to be easily readable, up to you.
With jQuery, the most common way to trigger on ready is

$( function(){
  //Do Something
  menuBreak();
});


now, since $() expects a function, we might as well pass menuBreak immediately:

$( menuBreak );


The same things goes for resize:

$(window).resize( menuBreak );