i need to convert a 700r4 out of an 89 firebird to cable speedo from and electric speedo.

Thats what I was wondering...Any ideas anyone?

I have seen those conversions for sale. One thing I believe you need to do is change the speedo gear on the 700R4 tail shaft from plastic to metal. I'm sure that would be in the kit.

With an electronic speedo it isn't a gear anymore; it's a reluctor wheel. The VSS "sees" the spaces between the "teeth" and transmits the rate as a wave to the speedometer and ECM. The frequency of the wave is used to interpolate the speed of the output shaft. I believe that the cars used some kind of adjustment box in-line between the sensor and the speedo to account for different rear gear ratios and/or tire sizes.

But you want to go the other way, which is way easier. Just swap the reluctor for a speedo gear (I think these are still available from GM) and install your speedo sender and connect the cable. You can swap the driven gear as needed for gear ratio and tire size.

On 3rd gen f-body's the VSS for electric speedometers uses a two-gear set up. The VSS is magnetic and produces 4K pulses per mile. The drive & driven gears can be changed for different rear ratios and tire diameters.

red/white04, just get a VSS assembly from an earlier 700R4. They bolt in directly in place of the mag type VSS. Note that there are different housings dependent upon the drive/driven gears used. It has to do with the offset required from the various gear diameters.

Note that I don't have any informaiton on which housing is used with which gears. So I can't help there.

RBob.