My speedometer does not seem to be working correctly. It bounces all over and makes a ringing noise like a small bell being struck. I am sure the problem is in the head and will be changing to a mechanical Autometer speedometer this week. Because of the problem with the speedometer I can not determine if the gear on the cable is the correct one.
Currently the cable has the red 21 tooth driven gear installed. My rear gear is a 3.73 and tire size is 255R60/15.
Can you verify the driven gear size is correct and if not recommend the correct tooth count to install.
Thanks.

No should be an 18 tooth gear

Gene The factory speedometer was very inaccurate no matter which driven gear was installed. I installed an Autometer Pro Comp Speedometer and Tachometer last week. After the speedometer was installed and trying a 19, 20, 21 and 23 tooth gears the 21 dialed it in with less than a 2% error. The drive gear inside is yellow, I wasn't able to determine the number of teeth on it.


http://i80.photobucket.com/albums/j199/64elcamino/77%20Nova%20project/interior/dashupgrade3.jpg

The stock set up

http://i80.photobucket.com/albums/j199/64elcamino/77%20Nova%20project/interior/stockdash.jpg

http://www.chevelles.com/shop/speedo.html