C# XAML ScrollViewer to work without MaxHeight

C# XAML ScrollViewer to work without MaxHeight

I have a grid that further down have a StackPanel. I have defined the
row's height for the last to be "*", and in this very last row, is where
the StackPanel and all the control would inhabit.
So I have the bellow code in XAML for my StackPanel
<StackPanel Grid.Row="1" MaxHeight="333">
<StackPanel MaxHeight="333">
<ScrollViewer MaxHeight="333">
<TextBlock x:Name="lblRouteDetail" FontSize="35"
TextWrapping="Wrap"/>
</ScrollViewer>
</StackPanel>
</StackPanel>
Well, it worked, only that I have to constraint that the MaxHeight is 333,
without that, it won't work; the ScrollViewer won't work, the content in
the TextBlock wouldn't be scrollable.
Could you state where is my problem, and how to fix this things up?