to williammoore2

I replaced my 85 mph with a 165 mph in my 81 and only had to remove lower dash panel under steering column, remove duct under column then drop two bolts in column to lower column.  IF you have push in style speedo, you push the bracket and it should pop out, then you lower it - the gauge package and you remove (1) screw 7/32 head and remove the plug for gauges and note which direction it plugs in and you can then remove the entire gauge package.

 

fI have a 1978 did not have to drop the stering column to get speedo and tach out. sent the speedo to Corvette Specialties of  Maryland looked at it and repaired it in 2 days had it back in no time.  speedo bouncing check that it is not the speedo cable going into the transmission with the plastic gear, if the gear is slipping or moving the speedo wil be bouncing like mine, had to put in  a new retaining clip for the gear to stay in position and bouncing stopped. Also could be transducer . Again I was very pleased with Corvette Specialties. Good Luck

If your speedo is jumping, it is more likely the speedo cable causing the problem then the speedo.  You will probably need to either lube the rotating center part by pulling it out of the cable housing and lubing, then reinstalling in the housing, or just replacing the housing/cable assy.