auto transmission questions

[teebone]

Does anyone know if there is an output shaft speed sensor relaying info to the ECU?
If I change the rear gearing does the ECU need to be changed or recalibrated in any way?

 

[IJ.]

Depends on the car, if it has ABS there are 2 speed sensors, one on the trans and one behind the speedo, non ABS cars only have the one behind the speedo.

No they don't need calibration.

 

[Nick M]

You will want the speedo drive gear from the transmission that the diff came from. If you want the speedo to work right.