can anyone provide info on the 1969 Z28 m-21 speedo "drive gear" size (seems there are 2), just changed the rear end gear from 4:10 to 3:42 and need to change the driven gear to match the new rear gear
Not only are there more than one... there are adapters which change the speed as well. There was never a 3.42 available with the 69Z you are going to have to figure out your current speed using someone pacing you then convert to how much slower/faster you need the driven gear to be spinning.
One thing to note - If your tire height is not the same as OE (approx 26") then you are already off.
Info is on the Chevelle site. http://chevellestuff.net/tech/speedo.htm
Quote from: firstgenaddict on April 16, 2022, 01:07:02 PM
Not only are there more than one... there are adapters which change the speed as well. There was never a 3.42 available with the 69Z you are going to have to figure out your current speed using someone pacing you then convert to how much slower/faster you need the driven gear to be spinning.
One thing to note - If your tire height is not the same as OE (approx 26") then you are already off.
Could just install a GPS speed app on your phone to get accurate speed and use that for your calculations.