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Discussion Starter #1
Just upgraded the rear end on my '67 from 2.79 to 3.55. The old speedo gear (driven gear) was 18 tooth. According to my calculations, I now need a 22 tooth--which they don't make (the biggest has 21 teeth)!

What can I do?

Corcoran & Davis' Resto Guide says the drive gear is "part of the transmission output shaft," which makes it sound like it's not replaceable.

What, oh what can I do?
 

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Speedometer shops use speedometer "gearboxes" that will correct your speedometer error.

You didn't specify what car or transmission you were working on, but automatics do not have a replaceable drive gear.
 
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Had the same situation. As the previous post said you can chose a 21 or 23. I chose a 23 (from Steeda) since I actually needed like a 22.3 but the I read somewhere that the 23's wear out because the teeth or so small. Being within one tooth is close enough for most of us.
 
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Had the same situation. As the previous post said you can chose a 21 or 23. I chose a 23 (from Steeda) since I actually needed like a 22.3 but then I read somewhere that the 23's wear out because the teeth or so small. Being within one tooth is close enough for most of us.
 

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With my tires 225-60 x14's I need something between a 21 and 22, so I am going to go with a 21. You will be off less than 5% with a 21 if a 22 would be dead nuts on. 3-4mph at highway speed is not bad.

In my mind it is better to error by having the speedo read to fast than too slow. I'm less likely to speed.
 
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Thanks for the suggestions!
According to my calculations, I need a 21.8 tooth gear (for a ’67 C4), so a 21 tooth gear is closer than a 23. Plus, I agree with Chris that it’s better to overestimate speed (especially in Wisconsin, where speeding tickets are the main source of municipal revenue). I can live with a 4% error (21/21.9 = 96% -- is this the correct calculation?). Plus, it’ll make my MPG look better!
Thanks again,
Steve
 
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