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Old 05-25-2009, 09:52 PM
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calibrating speedometer gears

Just wondering if anyone has a formula for determining the proper speedo gears to use. My ride has a 350 turbo trans, 8in ford rear end with 3:00 gears and P255/ 70R rear tires. The speedo gears in the tranny now are reading about 5-10 MPH low. I've been told there is formula for figuring this out, any help would be appreciated.

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Old 05-25-2009, 10:11 PM
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I believe this link is what you're lookin for.

http://www.transmissioncenter.net/sp...____va.htm#350
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Old 05-25-2009, 10:49 PM
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Thanks for the link, great site,and lots of info, I'll have to get out the calculator
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Old 05-25-2009, 11:04 PM
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This site does the calculating for you.
http://www.bgsoflex.com/speedo1.html

Check this one as well
http://chevelleengineer.home.comcast...eer/speedo.htm
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Old 05-26-2009, 01:09 AM
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Quote:
Originally Posted by vanislander
Just wondering if anyone has a formula for determining the proper speedo gears to use. My ride has a 350 turbo trans, 8in ford rear end with 3:00 gears and P255/ 70R rear tires. The speedo gears in the tranny now are reading about 5-10 MPH low. I've been told there is formula for figuring this out, any help would be appreciated.
Reading 5-10 mph low? At what speed? 10 mph or 100 mph???

Calculate the PERCENTAGE that the speedometer reads low, then use that same percentage to DECREASE the number of teeth on your current DRIVEN gear.

Most likely that is all you will need to do.

There is a chance that you may need to INCREASE the tooth count on your DRIVE gear by ONE tooth. If that is the case, a little simple math using your percentage will tell you the tooth count of the needed driven gear. If you need to increase the tooth count on the drive gear you will also need to increase the tooth count on your driven gear.
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Old 05-26-2009, 01:49 AM
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Thanks all for the help, these forums are a wealth of info,especially for us newbe's
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