mark69sportsroof 31 Report post Posted February 21, 2017 Hi Everyone, I'm trying to figure out the correct speedo gear for my 69. It seems that I have seen a formula to determine the correct gear but I do not remember where or when I saw. Listed below is the key information if that helps. FE 390 stroked out to 445ci T-5 transmission 3:50 Pos rear end No A/C Weight - approx 3400 pounds Thanks Mark 6 yapedVem, Trmjam, rapedVem and 3 others reacted to this Quote Share this post Link to post Share on other sites
jgkurz 52 Report post Posted February 21, 2017 Hi Everyone, I'm trying to figure out the correct speedo gear for my 69. It seems that I have seen a formula to determine the correct gear but I do not remember where or when I saw. Listed below is the key information if that helps. FE 390 stroked out to 445ci T-5 transmission 3:50 Pos rear end No A/C Weight - approx 3400 pounds Thanks Mark You'll need to know your rear tire diameter and the "drive" gear inside the T-5. These tools should help. http://www.wallaceracing.com/tire-aspect-calc.php http://www.classic-cougar.com/tools/speedocalc/speedocalc.php Quote Share this post Link to post Share on other sites
BillC 38 Report post Posted February 21, 2017 Mark, I went through this when wheels were changed from 14" to 15". Here's a simple way to determine the correct speedo gear. I used a GPS to get the correct speed. Take your speedo cable out of the transmission. Count the teeth on the gear. Add teeth if speedo reads too fast. One tooth equals 5 mph. Deduct teeth if speedo is too slow. P.S. Change the gear retainer while your doing the gear. They are very brittle and will probably break when you remove the gear. Quote Share this post Link to post Share on other sites
mark69sportsroof 31 Report post Posted February 23, 2017 Thanks guys for the info. I drove it on the street and highway and used my GPS and my speedo was 10 mph was 10 mph faster then the GPS. I have a a 19 tooth gear so I need to get a 21 tooth gear if I read the Bill's response. Mark Quote Share this post Link to post Share on other sites