Speedo calibration VSS in Scan not same as speedo

[maudyZ28]

Which of the speedo calibration parameters, if any actually control the speedometer output? I believe the scan tool speed is correct to GSP pretty much but my actual speedo in the gauge cluster is off by about 5 km/h ?? Do I just have to fudge it all so the my cluster speedo is correct and just adjust the trans shifts etc about that point knowing they are slightly different??

thanks

[gmh308]

Which of the speedo calibration parameters, if any actually control the speedometer output? I believe the scan tool speed is correct to GSP pretty much but my actual speedo in the gauge cluster is off by about 5 km/h ?? Do I just have to fudge it all so the my cluster speedo is correct and just adjust the trans shifts etc about that point knowing they are slightly different??

thanks

The trans normally shifts based on scanned PID value which is pretty accurate as you have tested. The speedo is a corrected reading to meet various regulations/norms to generally read higher than actual.

[Ira]

Having tried to correctly put the speedo needle back on 100 or more F body clusters or so, I can assure you that it's being off is more likely than not. I try to make them right at 60 and sometimes that makes it perfect everywhere and others it can be right at 60 and 7 MPH off at 20. If it's off the same amount everywhere, use a GPS to check it, then just pull the needle and put it back on in a slightly different spot. turn on the car and wait for the needle to settle, then take a piece of tape and mark where it should point, then carefully pry it off and put it back on pointing at the new spot. It might take a few tries, the weight of the needle will move it as will just pushing it on.

Ira