The tach on my 1978 (L48) was replaced last year by the previous owner but it does not register any readings above 3500 rpm. Any reving past that point causes the needle to drop to bottom and then return when rpm's get below 3500. Any suggestions?

I believe the 78 has an electronic board in it, they are available from any of the corvette supply houses, send an email to Ernie at wilcox Corvette and ask him if he thinks it would fix your problem There is little Ernie doesn't know about 'Vettes

- Greg Greene
75 Coupe

Also check the tach filter. It's next to the distributor inline w/ the wire that plugs into the "TACH" terminal of the dist. Sometimes these with give you messed up tach readings.
Sarge