mrit

Im new to Corvettes still, Just picked up a 75 with 90k on it yesterday. Its got a few problems, but was worth the $4000. I believe that I read on here that 75 and earlier had the mech tachs. My problem is that my tach is constantly at 7000 rpm, even when its shut down, rev it up and it moves only a little. Any Ideas?

chris75stingray

the 75 has an electronic tach. there is a circut board behind it ,underneath the dash. most likely that is whats bad. mine doesn't work either.

G dad

There is a tach filter tha is supposed to go between the distributor & the tach wire, it looks like a noise suppression cap but it is designed to eliminate spikes that whack your tach! This could be the priblem...all the aftermarket corvette suppliers have them oh yeah...about $50

mrit

I think I remember reading about that a few days ago, Thats the thing with the little gear that bolts to the dist.

I'll try to check both those things out tomarrow.

Thanks

Kilroy1024

The external filter is to reduce radio interference being taken into the cockpit.

If the tach was working properly and the filter was open or shorted, the reading would go to 0 RPM.
Since yours is always reading 7000 - I would say your tach is most likely dead.

Battery reversal will instantly kill some of the early electronic tachs (75, 76). If it has a burnt out trace, you might be able to fix it.