65 barracuda vibration

So I just recently dropped the stock rearend on my 65 cuda and moved the leaf springs in to fit wider tires. I also went to a shortened 8 3/4 and put a spool in it. Everything seemed to go together just fine. Yesterday I finally got the chance to drive it up and down the street to just test the rearend. Well I hardly got over 10mph because the whole rearend was shaking so bad. Made the entire car vibrate. I was hoping someone had some ideas of what to check.