I am getting conflicting information on how to change the speedometer reading. My car had a 2.73 rear end which had rusted spring perches (it came from the salt belt where it had few miles but lots of salt).

I changed out the entire rear end for one with a 3.27 ratio. Now, of course, the speedometer is reading about 20% too fast. Some have suggested that there is a gear in the transmission on the VSS that I can change but I am unable to find sources for multiple gears. Some have suggested that the change is done with a programmer - but mine (OBD-2) reads the VSS and calibrates speed by the VSS signal times time...so there is no rear ratio, tire size, etc. to input.

Does anyone know how to calibrate the speed/mileage? If it is a plastic gear like on my old Ford car, where can I get them?

Thanks in advance,
Randy