Speedometer bouncing

Turn it slower with your drill, like 50 rpm instead of 500 rpm.

Make sure the speedo head is clean and a little WD-40 lube on the bearing shafts, then blow off the excess WD-40 with low pressure air. Being careful not to blow the WD-40 Lube up onto the black speedo face. Then test again.

Usually a dry speedometer cable when it is in the car will make it bounce. There are special cable lubricants available out there just for this.