Speedo Cable Replacement
I recently replaced my Vette's speedo cable - I have a 1977. Things more or less should be the same between our two models... perhaps my experience will help you.
I removed the entire driver's side dash - for the first time and with no references to guide me. What a headache - my girlfriend nearly disowned me for all the time I spent on this project - it took at least ten hours. Why so long? Again, I had no clue what I was doing and I relied instead on one of my strengths - being able to reverse engineer things back into place.
First, the steering column needed to be lowered - two sets of double bolts, one by the fire wall, the other further up the column. Even then it lowered only an inch. The driver's side dash was in too tight - to make things easier I removed the passenger side dash and unbolted the center dash piece; the latter I moved to the right a few inches.
Then the headlight vacuum hoses and the main electrical harness needed to be disconnected - there was barely enough room to squeeze my hand inside that narrow space. The speedo cable itself is held on by a clip - that alone took a half hour to disconnect. In the end, by easing the dash pad out, despite all my effort, four of twelve dash light wires snapped.
I figured out where the speedo cable entered the interior of the car from the engine compartment but had no clue how to pull it out - a rubber seal surrounded the cable by the firewall. Did I have to pull the rubber seal out? There was no way to get a firm grip on it. Taking a blind leap of faith I simply pulled on the cable and out it popped. I then traced the cable to the transmission (with the Vette jacked up) and the old cable simply screwed off.
Putting the new cable in I discovered was relatively easy. It screwed onto the transmission and was pushed through the rubber seal.
Then came the long and hard part. Those broken dash light wires needed to be resoldered. Figuring where they came from wasn't as difficult as I expected but still a nightmare because of the tiny working area. Slowly but surely everything was carefully put pack into place - it took more than three tries because things (wires, vacuum hoses, wiring harness) had to be in certain spots to fit and ground connections kept disconnecting. I had a tough time lining up air ducts, too.
After all this work I looked back at what could have been done differently. I discovered that the dash pad didn't have to come off at all. I only needed to remove a small panel under the driver's side dash to allow me to reach the clip holding onto the cable. I then could've pulled the cable out from the engine compartment - and pushed the new one through again. Reaching under the dash I could've caught the new cable and clipped it onto the speedo.
A lesson learned the hard way - don’t do what I did. I hope your Vette is similar to mine and that your dash doesn’t have to be removed.
