I ran slapper bars (unjust name IMO) on a 70 Nova with single leaf rear springs, and they were quite. These were high quality ones that replaced the lower spring pad. It totally eliminated rear wheel hop. I raced that Nova every Wednesday night and on weekends at the Abilene Texas drag strip the entire time I was stationed there. The only down side was after a while the snubber started bending the leaf spring where it contacted it. Also over time the spring perches on the 10 bolt axle started to roll off the axle tubes. I however never did break the 10 bolt gear set, in spite of me trying.