Speedometer Help
 

I have a 70 Fleetside with a M20 4sp manual transmission. The original rear end gear was a 3.73, it has been replaced with a 3.07. The speedometer is off, does anyone know who would sell the calibration gear for the 3.07 so the speedometer reads correctly.

Go to http://novaresource.org/speedo.htm & you can use your axle ratio & tire diameter to calculate the speedo gear ratio you need. If you get lucky, you can use the drive gear that's already on your trans output shaft & only change the driven gear, which should be available at the nearest Chevy place. If not, you can get a drive gear at http://www.dandltransmission.com/muncie.html (you'll need to know if the drive gear is metal or plastic, as the metal ones are pressed on & the plastic ones use a retaining clip).

Just because it might be easier, count the teeth on your driven gear (the one the speedo cable hooks to) & multiply by 3.07 & divide by 3.73. If it comes out a whole number (or close) between 18 & 23, just get a driven gear with that many teeth.

I just went through this with my 400 turbo. This is a great website too.
http://www.bgsoflex.com/speedo1.html
Find out what your drive gear and driven gear (sppedo housing on my auto not sure on yours) is and go from there. Maybe you will get lucky and you will not have to get it swapped like I did.

All, thanks so much, I appreciate the information and fast turnaround. Again many thanks