Which speedo gears to put after a 3.73 gears on a 98 GT?


New Member
Sep 23, 2018
Miami, FL
98 GT with an OEM T45 8 drive teeth Manual transmission .

Recently I swapped gears from 2.73 to 3.73. My speedometer shows incorrect speed (15-20 mph difference) after the gear swap. I believe I need to change the driven gears but I don't know which ones to put.I have 285/40/17 in the rear. I searched around different forums and people suggest 21 teeth driven speedo gears for my car. Can anyone confirm this? I used the CJPonyParts driven gear calculator and it suggested the 23 teeth driven speedo gears but also mentioned that they should not be put on a T45 transmission because they will get damaged easily.
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I used this when I changed the rear end in my car, went from 2:73:1 to an axle with 3:27:1 and it was correct

I used that calculator and it says that I should used the 23 teeth drive gear but then in the "considerations" section it says that the 23 teeth should not be put with my trans as the speedo gears will get damaged.