CRG Discussion Forum
Camaro Research Group Discussion => Mild Modifications => Topic started by: steve6755 on April 16, 2022, 04:24:39 PM
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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
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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.
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Info is on the Chevelle site. http://chevellestuff.net/tech/speedo.htm
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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.