speedo not matching computer when logging

[badls1]

ive been trying to calibrate my speedo in a 2001 Camaro. I finally got the reading on the computer when im logging to match my actual speed but the speedometer in the car does not match this. how can I correct this and make them both the same?

[joecar]

What trans, axle ratio, tire size...?

[badls1]

th400, 3.42, 26" tire

[badls1]

and im reading speed off the speed sensor on the rear of the tranny

[ferocity02]

First you want to match your OBD speed to your GPS speed using the settings in the tune. Then if the speedometer in the cluster is off from the OBD speed you need to literally pull the needle off the gauge stepper motor and move it so it reads correctly. If you match it at one speed it might be slightly off at another speed. You won't get it perfect. I matched my speedo to my OBD at 65 mph since I think its important for it to be accurate at that speed (to avoid speeding tickets).

[Big Mike]

Why not use the speedo fine tuning feature in the software to adjust the actual speedo head? Isn't that what it's for?

[ferocity02]

Why not use the speedo fine tuning feature in the software to adjust the actual speedo head? Isn't that what it's for?

No, that's for fine tuning the OBD speed beyond using the gear ratios and tire size, for variables such as tire wear, manufacturer's diameter tolerance, tire pressure, basically things that would make minor differences to the tire diameter. Using the gear ratio and tire size I got within a couple percent of GPS speed, then use the fine tuning to get it pretty much spot on.

The speedo in the cluster is meant to display OBD speed, but only if the needle is calibrated, as in manually adjusting the needling on the stepper motor.

One thing that bothered me is that the fine tuning tool will only change H0101 Vehicle Speed Sensor Pulses per Mile. However it should also change H0104 Trans Output Shaft Revs/Mile, which unless I'm mistaken, should equal the pulses per mile divided by the pulses per revolution (H0102). I adjusted it and it made no difference in my OBD speed. The description says its used for transmission shift speeds in auto, and not used for manuals.

[joecar]

th400, 3.42, 26" tire

For the THM400 are you using a 40-tooth reluctor...?

In the tunetool did you enter/compute for 3.42 axle and 26" tire diameter...?

Did you un-checkmark Transaxle...?

Post screenshots of the speedo parameters and of the Speedo Calulator.