I dont know if this is in the right place or not so if it ant then sorry.But a few of yall have said that if my speedo is off then it will show crap fuel mileage. And i know that mine is off by bout 10 mph. So what it ant easy cheap why to fix the speedo. Thanks fer the help yall.

Easiest way is not cheap. That would be to figure out how much in %, and then get a 'speedo adapter" gearbox. Takes less than a minute to install.

More work, but cheaper is to get the correct "driven" speedo gear. If you get lucky, you may not need to change the drive gear which is more work. You won't know until you find out the exact error you have in %, and then find out what drive & driven gears you have...then go to GM and they can look up the corrections. They may prefer you give them your axle ratio, tire size, etc, instead..

Way too much screwing around for me. Just ante up, and buy the adapter

By the way, you can't just say my speedo is off by 10. Get on a hiway with mile markers and compute the percentage.

These may help you
http://4lo.com/calc/geartire.htm
http://www.miata.net/garage/tirecalc.html
Shane

http://novaresource.org/speedo.htm has a formula that uses tire diameter & rear end gear ratio, and a chart of speedo gear combinations.

http://tciauto.com/Products/TechInfo/speedo_gears.asp has a tire diameter calculator.

If you know you are 10% off, just factor in that 10%.....There, it cost you nothing......That will be 29.95 for the advise.................

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Thanks fer all the heop guys.I had no idea that it would be that envolved to fix that thing.But it will be a long project so i ant in to big of a hurry on something that small.Thanks agian.

It's not really involved or difficult

When I recalibrate a build, I just go out on the highway here that has mile markers each mile. I go 10 miles. Let's say after the 10th mile, I have gained 1 mile too much on the odometer...that means you need to slow down the speedo cable approximately 10%. Then just get the 10% reducing adapter. I also use a watch with a second hand, to time each mile, or just hold it at a steady 60mph for those 10 miles, to see if the error is the same on speed, as well as "miles driven".