I am making some changes to my 68 which require a THM400 Driven gear change. When I got the car it was running the standard 14x6 wheel with 2.56 gears. I put on some 15x7s, and will shortly upgrade the rear gears. Need some help in determining the new Driven Gear to use.

Using my trusty Ames Performance catalog they give the following formula:
Number of Drive Teeth x Axle Ratio x Tire Revolutions per Mile all divided by 1001 to get the Number of Speedometer Driven Teeth.

My new Axle Ration is 3.08 (found NOS set via Smoke Signals)
My Tire Revolutions per Mile is 842
How do I determine my Number of Drive Teeth?

BTW - Engine and tranny are still in the car.

Follow this link.

http://www.bgsoflex.com/speedo1.html

Jeff,

Thanks for the link but I'm not understanding how it helps me. My 15x7 tire diameter is 24.7 and my gear ration is 3.08 but the calculator requires either Drive Teeth count or Driven Gear count. I don't know either of those. If I understand the formula I need to determine my Drive Teeth count to figure out which Driven gear to use. What am I missing?

Thanks

Have you driven the car since the changes were made? Use a gps to determine your speed and that will tell you how much on an adjustment you need to make.
The driven gear is easy to get at, count the teeth and adjust from there. Good luck.

What Hank said.