I think I know the answer, but thought it better to get some more opinions, the odometer still works but the speedo does not, does the whole speedo unit have to be replaced? Thanks for the help.

 

I think speedos are a problem in these cars mine bobbles up and down between 5 mph evertime i go over 50

 

Upgrade the guages to autometer C2's they look so tight. That is what im gonna do to mine this summer. It gives off a cool led blue. Check out the autometer website

 

Well, I'm not sure either, but I'll be taking mine out tonite. I think that it is two seperate things, so you might be able to fix the speedo problem. Is the speedo working at all, or is it doing the bouncing thing? If it's sort of working, but bouncing, it's usually one of the cables binding. On my 80, I have a long cable going from the tranny to the cruise control box and a short one going from the CC box to the speedo. If there are any severe bends in either cable, it will cause bouncing. I shoot some aerosol white grease down the cable casings every once in a while. If it's not the cable, it could be the CC box itself, if you have one. I discovered that it was my CC box causing the bouncing by connecting the short cable to a variable speed drill.

I think the odometer is mechanical, but the speedo utilizes a rotating magnetic ring that encircles a coil spring that is connected to the needle shaft. I don't think that there is any physical connection between the cable and the actual needle shaft. As the magnetic ring rotates, it exerts force against the spring, coiling it tighter and causing the needle to move. You might be able to get in there and see if the spring is jammed up, or there is crud accumulated where the needle post goes throught the face of the speedo.
Hope this helps a little, and if anyone knows that I'm off the mark on the speedo operation, please chime in.

 

Here's a past thread on the same problem

http://forums.corvetteforum.com/show...dometer+repair

you can see others by search on speedometer repair