Tachometer

03-16-04, 08:37 AM

My 1980 had a non-functioning tach. So after studying Eckler's which says, "95% of the problem with these tachs is the printed circuit board",I ordered one. Still no tach. What's your experience with these tachs? Also, where is the relay for the power antenna located? Sounds like it's back by the emergency brake handle.

Copdogcorvettes · 03-16-04, 01:04 PM

One other thing on the tach is the filter. There is a inline tach filter coming from the dist. When I got my 80 the tach didn't work; I discovered the the tach filter had been removed, so I replaced that. Kinda pricey $60 -$70. Then I found that the circuit board was bad as well. Another $60, but it worked great after that.

So I'd guess you better look for the filter.

Gary

tom102 · 03-16-04, 01:49 PM

Try this site, I replaced my tach filter from them a few weeks ago and tach works perfectly now. The GM filter has been discontinued and he makes a exact replacement for $50
http://my.execpc.com/~rodney1/corvette/

Stallion · 03-16-04, 02:30 PM

What is the filter used to filter out?

03-17-04, 07:58 AM

Thanks guys. I'll check on that filter!

citruspilot · 03-17-04, 08:24 AM

Ive got a tach problem too. Mine stays in the 3,500 RPM range all the time. Even while the engine is off. I start up the engine, the tach drops to about 3,100 RPM's then heads right back to the 3,500 region. If I drive the car and smash the gas the tach will catch the engine PRM only when the engine RPM's exceed the range of the RPM being shown on the tach. Again, unually around 3,500 RPM's.

My friend who is helping me with my engine clean-up project tested the tach filter and said it was OK. Ohm meter I guess. So I guess the next thing to do is buy the circuit board for the dash unless anyone in here has a better cheaper fix??? Just trying to save a buck. I have already spent over $400.00 on paint/original replacement parts/fluids/hoses/belts/cleaners/etc. and Im not even done yet. My wife is starting to ask the questions like "What is this costing you?" This was supposed to be a two day fun project. Its turned in a two week job instead!

However it will look very nice and original stock when I show up at the AutoFare car show in Charlotte on April 1st. I'm excited!!! The greasy hands, cuts and bruises will be worth it in the end I am sure!

Thanks for the help as usual folks.

Jeff

(One day I'll figure out how to post my pics in here. Ive got some good ones. Ive tried but my files are too big it seems wont upload into the site. Any suggestions on how to make them fit?)

tom102 · 03-17-04, 10:28 AM

Stallion

It's main function is to filter out the electrical spikes so that your tach goes up and down smoothly instead of bouncing. A burnt out one can result in erractic tach readings ( needle dance) or sometimes no tach reading at all. One word of caution when replacing is never let the tach wire from the HEI touch ground as it can burn up your coil and Ignition module.

Stallion · 03-17-04, 03:14 PM

Ah I see, Tom. Thanks!

03-20-04, 05:01 PM

O.K. I looked at my distributor and there is a projection which is marked"tach" and I think the other is ground. There is no wire on the tach terminal. Is this a clue? What color should the tach wire be? Eternally grateful....

miratech · 03-21-04, 08:38 AM

Quote:

Originally Posted by David Evans

O.K. I looked at my distributor and there is a projection which is marked"tach" and I think the other is ground. There is no wire on the tach terminal. Is this a clue? What color should the tach wire be? Eternally grateful....

Yes, you must have this wire connected. This is the signal that is read by the tachometer. Not sure what color wire is on an 80, but my 76 is brown. Since you already have changed the circuit board behind the tach, you can look to see what color the wire is from there and trace it back into the firewall. Then under the hood look for the same wire and connect up to the TACH terminal on the distributor.