chrled

-79 L48 Stock
My speedometer and odometer just stopped working. The speedo had been jumping for a while on low speeds but now nothing is moving. No speed, no odo no trip. What todo and what is the problem. Is it the cable?

Thanks.
Chris, South Florida

Captain Morgan

More than likely it's the cable. However, it could be that the driven gear inside the tranny has flatspotted. Happened to me. $2.00 part at the chevy dealer and an easy install.

Take the cable off the tranny side and put a drill on the cable. Run the drill, starting at low rpms and working upwards and see if the speedo moves. YOu may have to run the drill in reverse, can't remember. If the speedo moves, then the cable is fine. If not, then the cable is probably broken, or the speedo is bound up. If the speedo moves then next thing to check is the gear in the tranny. Look at where the cable goes into the tranny. There will be a small bolt next to it (maybe a 3/8ths head). Loosen that bolt and move the little metal piece that holds the gear into the tranny. Now pull the gear out and check it out, looking for any 'worn' teeth.

By the way, if you have cruise, you will have two cables. One from the tranny to the cruise transducer and one from the cruise to the speedo. Let us know what you find.

DaBo

YEP....

Probably cable.
Mine was jumpy for a while and then quit.

76 had a 2 piece cable, I replaced with a 1 piece.

gearheadz

Barring a failure of the speedo needle shaft or drum or the tranny gear, the cable would be the prime suspect if you get no needle movement. If it was just the odometer that wasn't working, one of the two odometer gears would be the prime suspects. You isolate the cable by removing the cable from the back of the speedo & spinning the speedo shaft by hand to see if you get movement. If you do, its the cable...if not its an internal speedo problem. The cable is attached to the speedo housing by a clip where the cable enters the back of the speedo that when depressed lets the cable be seperated. It will be a tight squeeze but you can do it without dropping the dash.

Mark


[Modified by mdsmith, 12:00 AM 2/26/2002]

Captain Morgan

That's why I used the drill method when I tested mine. It was much easier to get to as I could lay on the floor of the garage. It's a pain to get to now because the dual exhaust is routed closer to the tranny.

chrled

Thanks a lot!
I have a cruise, not working though. It is on the todo list.
Does the fact that i have a non-working cruise affect my odo/speed problem?

Thanks! Chris

Captain Morgan

That depends. Did they quit working at the same time or has the cruise not been working for a long time? If they quit at the same time, it could still be the cable. The cruise can't work without an input.

Sounds to me like they quit at different times. If that is the case, then the cruise should not affect the speedo. Since you do have the cruise, you will have two different cables that can break. Check both of them, sounds like one broke since the speedo was bouncing before it quit.

Neo Fender

Most of the speedo cable failures in cruise control equipped C3s are caused by the cruise control transducer. I just replaced one in my '79. If you notice that the needle was twitching before the speedometer died, it's probably an indication that the transducer is binding, causing the cable to break, usually the lower one.

A rebuilt trasnducer is anywhere from $60 to $95. I bought mine from a salvage yard for $25. If you go this route, make sure you can exchange it if it doesn't work. About 50% of the transducers in the yards are probably already AFU.