My speedometer bounces while driving my car instead of having smooth needle movement in the dash. Where do I need to look to get rid of the problem? Would it be in the transmission (i.e. the little plastic gear), the cable, or the speedometer in the dash itself? Its hard to tell whether I'm doing 25 or 35 mph and really seems to get worse when I speed up.

Most likely is the cable, then the gauge itself and last the transmission. You can rule out the transmission by loosening the cable from it and drive the inner cable with an electric drill.

Most cables I have allow removing the inner cable (from the gauge's side). This way you can inspect the inner cable and grease it.

Hope this helps.

Rob