I have a 87 Trans Am 350 TPI with a 5-spd that has 3.73 gears, My spedo is off about 15 MPH and I'm changing the spedo gears inside, What was in it was a red drive with 9 teeth, I'm installing a purple drive gear with 7 teeth, now do I also need to change the driven gear? What is in is a gray 22 tooth gear. Should I change it to one with a lower number of teeth they list a 20 and a 19 tooth gears. I would like it to be as close to the correct spped as possible but don't want it to show say 55 when I'm only going 50, 1-2 MPH over or below would be fine. Thanks for any help on this, jason

 

A 19 or 20 will get you real close,Depending on your tires. check this out it will give you a great calculation.
www.hanlonmotorsports.com.

 

Thanks, kjgroen I went to the site and they recommed a 7 tooth and a 21 tooth but I did not see a 21 tooth listed does anyone have a part number for the 21 tooth with a 5-spd?

 

Your dealer should have it, if it hasnt been discontinued. If not, Hanlon should have it, or www.gearzone.net or others. It should cost <$20

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