Speedometer not working

If both the speedometer and the odometer have stopped the problem is either the drive cable or the driven gear inside the tail shaft housing on the transmission. Basically you would put it on a lift so the rear tires are off the ground. Remove the speedometer cable (the end unscrews) from the housing. The start the car and put it in gear, then watch the speedometer drive to see if it moves. I usually stick a small hex key in there so I can apply some braking pressure in case the gear is only partly stripped. If that end checks out. You can sometimes reach up behind the dash cluster and push the release tab to get the upper end of the cable free. Then you need to route the replacement cable up through the firewall and into the dash. Connect both ends and you should be back in business.

If the lower drive isn't turning or skips, you look at the color of the gear and get that color replacement. Then you remove the drive housing, remove the damaged gear and slide in the new one. Bolt it back in, connect the cable and you are done.

Now if the odometer is still working but the speedometer needle is not. You will probably need to change the speedometer head out and lube the small drive shaft to the needle.