Insert slicing disc.
Slice cucumbers; transfer to a large mixing bowl.
Add onion and salt to cucumbers; stir to mix.
Cover with ice cubes and refrigerate for 2 to 3 hours.
Drain water from bowl and discard any un-melted ice cubes, but do not rinse cucumber mixture.
Pack cucumber mixture in freezer containers or jars, filling each to within 1 1/2 inches of rim.
In a 2 to 3-quart pan, combine sugar and vinegar.
Bring to a boil over high heat, stirring until sugar is dissolved.
Pour just enough hot syrup over cucumber mixture to cover.
Put lids in place and freeze pickles for at least 1 week.
Before serving, thaw in refrigerator for about 8 hours.