tiNnNy

The other night I hit some lady from behind in my civic. My speedometer was working fine before I hit her. After I hit her, my speedometer started to jump going from 0 to 80 then down to 40 to 100. I cleaned out the plug that goes to the speepometer on the tranny and I pushed the 3 wires down to make sure they didnt pop up. I did just recently add more tranny fluid on the tranny, but after I did that my speedometer still worked fine. What could it be?