Slice cucumbers to desired thickness. In a large bowl combine sliced cucumbers and salt. Cover and chill for 2 hours.
Rinse cucumbers in a colander. Drain well. Place back in the bowl and add onions.
Combine sugar and remaining ingredients in a saucepan and bring to a simmer over medium heat. Stir to dissolve sugars.
Fill the jars with the cucumber and onion slices. Fill to about 3/4 full.
Pour hot liquid into jars up to 1/4 inch headspace. Tap jars to let cucumbers settle. Add more cucumbers as long as you keep the headspace.
Add lids and rings. Process jars in a water bath for 15 minutes.
You can also refrigerate your pickles at this point without canning them. They will stay fresh for 2 weeks.
Give the pickles at least 24 hours for great flavor.