I just picked up an '86 Corvette with a built motor and trans. Speedometer not working and when I take out the speed sensor I see why, it has no gear on it. And the drive gear doesn't look like a regular plastic gear either.



I'm guessing it takes an electronic sensor and someone just put this original mechanical sensor in to plug the hole.



What transmission does it have if you can tell from the pan?



A TH400?

 

Its a 700r4 and that model vet would have had an electrical speedo so the sensor and reluctor gears are right for that model.

 

Here is the other side of the sensor I found in the transmission.



It takes a gear on the end so it can't be the right one.

 

Hmm late early mix you might try the later sensor and see if the PCM can be calibrated to use it with the reluctor wheel on the trans now