pw520a 19 Report post Posted July 1, 2021 I have a 69 390 c6 with 3.25 axle ratio and stock14 inch rims on car, the speedometer cable was missing the driven gear so I purchased on eBay a 16,17,18,19 and 20 tooth set ,does anybody know which one would be correct or which one to start with for correct speedometer reading? Quote Share this post Link to post Share on other sites
aslanefe 333 Report post Posted July 1, 2021 1 hour ago, pw520a said: I have a 69 390 c6 with 3.25 axle ratio and stock14 inch rims on car, the speedometer cable was missing the driven gear so I purchased on eBay a 16,17,18,19 and 20 tooth set ,does anybody know which one would be correct or which one to start with for correct speedometer reading? Don't know which one is correct, but I would start with 18 (the middle one) and check speedometer reading with GPS then go up or down if needed. At least it is easy to change the gear. 1 pw520a reacted to this Quote Share this post Link to post Share on other sites
pw520a 19 Report post Posted July 2, 2021 makes sense Thanks Quote Share this post Link to post Share on other sites
jmlay 80 Report post Posted July 2, 2021 Take a look at these: https://www.428cobrajet.org/speedo-gears https://www.428cobrajet.org/speedo-calc 1 pw520a reacted to this Quote Share this post Link to post Share on other sites
bigmal 225 Report post Posted July 2, 2021 As said above using the GPS. Plenty of cheap Speedo Apps for your phone that work vey well. As a rule of thumb I found each tooth equates to about 5% change. 2 pw520a and Mach1 Driver reacted to this Quote Share this post Link to post Share on other sites
det0326 179 Report post Posted July 3, 2021 Depends on what u want. If u don't care about your odometer being correct then changing the gears to make your speedo correct is fine. If u want the odometer correct as said put the 18 tooth one in and check the odometer reading for 1 mile. If it proves to be correct and speedo still not correct then u have a speedo problem. Quote Share this post Link to post Share on other sites
pw520a 19 Report post Posted July 4, 2021 GREAT INFORMATION JMLAY THANKS! Quote Share this post Link to post Share on other sites
jmlay 80 Report post Posted July 4, 2021 Anytime! Quote Share this post Link to post Share on other sites