Classic Instruments Speedometer

[cruisinthe34]

I'm running a new Classic Instruments speed ometer with a pulse generator attached to a 700R4.

On first driving the truck, everything seemed near perfect, even the Speedo without calibrating. But at 41 miles, the speedo quit registering either speed or miles. I thought I lost a ground or something. On checking the grounds, all seemed fine. I took the truck out again and the speedo seemed okay......for about 20 miles or so then nothing.

My next step is to disconnect the pulse generator and hook it up to a drill, power the dash instruments then spin the drill to see if I get an instrument response.

Only other thoughts are whether it is dying because it hasn't been calibrated (has dip switches on the back), or someone mentioned wiring through an SN-74 .

Any input appreciated.

[davepl]

Long shot, but it's got to be something that's changing or variable, could it be the spacing between the pickup and the magnet if you're using a driveshaft sensor?

[Overdriven]

Check your grounds! I forget the specifics as it was a few years ago but the speedo ground likes to grounded in a certain location. You wouldn't think it would make a difference but trust me it does. Went through similar trials and tribulations installing a Classic Instruments cluster in my fathers Nova and ended up replacing the pulse generator needlessly. Gave it the ground location it wanted (specified in the manual) and all the problems went away with both pulse generators working properly.

Edit: I'm going by fuzy memory on this. It may not have been the ground, it may have been one of the power wires. Either way the instructions are specific on where to ground (both the cluster and the speedo pulse generator) as well as where to take power and you should follow those instructions to the letter. Check your grounds and power wires to make sure they're going to places specified in the instructions. If all that checks out then maybe it is the signal generator, we did have one go bad eventually too.