How exactly does the whole speed sender and stuff on the trany work? All i know is that the 700r4 tranny sends 4000 pulses for every mile.. Thats all i know.. does the ECM send voltage to the speed sender and read what kinda of signal it gets back.. or does it read the signal that it sends.. in other words what are the two wires going to the speed sender? also any other information on what kind of signal it sends and how it derives this signal and just about any other information u can throw at me.. Im here to Learn!!

 

As far as I know, the sender itself is nothing more than a coil of wire. On the tranny output shaft is a magnet. As the magent spins, it induces a current in the coil. I think one of the two wires is ground or a reference, the other is the signal. The actual signal is a sine wave. As the speed of the car increases, the frequency of the signal AND the amplitude of the signal increase. Depending on the car, the signal either goes to the ECM first or a buffer. In either case, the signal is transformed into a digital signal, that is like a square wave signal. So now the signal only changes frequency with speed. After that transformation, the computer uses the digital signal to run the speedo, cruise control and speed limiter. But that the basics.

-Dave

 

Your description is impeccably accurate, except that on many VSS units the magnets and pickup (field) are contained within the unit and the VSS gets a plastic driven gear to turn it just like the old cabled speedometer drives.