I have a 1982 chev impala station wagon pretty plain, 305 v8 and 3 speed auto with lockup. I am having an ongoing problem with its speedometer. Originally the problem was a really jerky needle. It would go up the gauge fine until I would hit say 70km, as soon as I let off the gas the needle would drop immed to 60 and bounce back and fourth till around 35km. I replaced the speedometer cable and did not help. So I then greased the speedometer itself and nothing changed. Next step was total speedometer replacement. That worked for about two blocks and now its doing it again. The cable is fine and speedometer itself is fine, there is nothing binding or bent at all. It just bounces up the gauge and steadies out but around 70km-80km it stays until I let off the gas then it bounces all over and won't steady out until I come to a compleate stop and start again. I have a feeling the speed is not acurate either. Can you plaese help me out. I'd like to avoid a ticket at all cost lol. Thanks for any input anyone can give me.

I think I read somewhere that poor grounds can cause that.

It doesn't hurt to try cleaning up your ground points.

You may want to check the speed-o gear in the trans . There are two one that rides on the rear shaft of the trans and one that the cable screws to

Yes, check the gear inside the transmission. The cable probably enters at the
Rear area of the trans around the output shaft housing.You have replaced
Everything beyond that so that is likeky the cause. Good Luck!