I bought a tranny which came with a mechanical speedo but my car is electronic. So I thought I would just swap the sending units and the plastic gear that is on the sending unit. Did the swap the speedo and odometer are not getting a reading. I heard that I must change the output gear on the tranny as well. What all is involved in that? Will I loose fluid, and can it be done with the tranny installed. Thanks

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Is the proper name for the gear in the tranny the out put shaft gear. Is this the one which should be metal instead of plastic? So when the swap is complete a metal gear will be driving a plastic gear?

 

Anyone enlighten me? Here is a link with a picture of the tail of a 700R4 looks like i need the silver metal piece to make it work correct?
Here is the link

 

The link you provided has some very good information on it.
The plastic speedo gear on the output shaft is the speedometer drive gear. You might have a plastic gear with an electronic speedo sender, to check pull it out of the side of the trans if it has a driven gear you need a plastic drive gear installed on your output shaft to go with it. If it has a magnetic pick up type sensor (no gear) you need the metal signal generator disc on your output shaft. To change the driven gear or metal disc you need to pull the tail housing off. If you jack the car up at the rear you'll lose a little fluid, not much. Obviously the driveshaft and torque arm has to come off too. Remove the drive gear or ring with a 1 1/4 (I think) open end wrench, slide it over the output shaft and use it to tap on the gear. Theres a clip on plastic gears and a slight press fit, the metal ring is a tighter press fit.