ok guys here's the deal- i just did new headers (to replace the old rusted ones), and it all went perfectly. i drove the car for two days (zz4 HSR with lt1 t56) and all was well. last night i turned the car off after driving for 15 min, went inside and got my wallet, 2 min later i get back in the car, the speedometer isnt working, neither is the odometer. all of the other gauges work, and when i turn the key to "ON", the needle on the speedo raises off the peg, so it has power. i checked all the fueses, looked for shorts, i cant find ANYTHING wrong, looked under the car, no damage from the header swap. im stumped. is my vss bad? or my dakota digital signal converter box? or my gauge? computer? the car runs perfectly still if that helps.. its one thing after another....

 

also if it helps, the speedometer was making a ticking/clicking noise since i bought the car

 

Maybe the new headers are closer to the wiring and melted the VSS wires? They drop down behind the engine with the tranny wires and follow along the tranny all the way to the tailshaft. Yellow and purple wires.

Does the cruise control work? (if it worked before)
If yes, the problem is inside the car, somewhere under the dash, not in the speed sensor or wires on the tranny.

If you search for VSS or speedometer here, you'll find a lot of thread that deal with it and a lot of ways to test different compoments.
And btw, your Z28 does NOT have the speed buffer box, in case you read otherwise.

Lou