I put rubber washers on both sides of my 11"dd thin ear...
I got them from the rubber washer bin at the hardware store...took my lower rod in there to size them up, I found some with the right diameter and the right thickness...thing is, the sides of the lower rod washer walls will Wow out a deep groove in those thin coil ears after a few years of heavy swinging...nearly saw it right off!...so I filed down those rod sides so the washers stood just a bit 'proud' and it sure seems to have helped..a guy can adjust the tightness of the coil bolt so you get a little bit of flap just how you like it....
if your coil is flopping around no matter how tight you have the coil bolt, no doubt you have deep grooves worn into the coil ears...If you catch it in time, you can fill the worn grooves in with JB weld, file off a bit of that lower rod washer detent area, essentially making it 'narrower' put some rubber washers in there, and have a Merry Christmas!

Mud