Tach accuracy - *NOT!*
Thread Starter
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Tach accuracy - *NOT!*
I just rebuilt the dash on the '76 and that included new clock, tach circuit board, all new lights. Also put a new tach filter under the hood. Took the tach down to the place that fixes these things and had him run it on the bench. He says it's accurate on the bench.
The circuit board instructions say to center the needle - which was done - on the '75 and '76 models. They say you want it to 'zero' with the key on, or on the bench with 12V applied to it. done.
Problem is that now the car's together and the tach isn't right. It reads at least 500 RPM high at idle, and much higher thru the power band. At 55MPH it shows 4500RPM and at 75, it shows well over 6K!
What the he** do I do now? It would have been so simple to just buy a tach and install it, but I wanted all the OEM stuff fixed so that's what I did. Or thought anyway!
The circuit board instructions say to center the needle - which was done - on the '75 and '76 models. They say you want it to 'zero' with the key on, or on the bench with 12V applied to it. done.
Problem is that now the car's together and the tach isn't right. It reads at least 500 RPM high at idle, and much higher thru the power band. At 55MPH it shows 4500RPM and at 75, it shows well over 6K!
What the he** do I do now? It would have been so simple to just buy a tach and install it, but I wanted all the OEM stuff fixed so that's what I did. Or thought anyway!
Thread Starter
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by cchristo
This might be a dumb question, but how do you know it's wrong? Have you hooked up an external tach to compare it to? I assume that before the dash rebuild, those figures were nowhere near that.
The tach had not moved a quiver since I got the car, til' this Summer. I put in a new tach filter and it still didn't do anything. So then in went the new circuit board. Then, it was 3500 RPM high - and when I researched it I found out that on the 75 and76 models you need to pull the needle and recenter it after doing the circuitboard. So when I had the dash out to fix lighting and the clock last week, I did just that and had it checked by the local speedo shop. I may just run by there and have him look at it.
Man this is frustrating!
<<At least my clock works now!>>
Burning Brakes
Joined: Jul 2003
Posts: 868
Likes: 5
Take the tach out there is an adjustment **** on the board provided you used one of the new styles.
Its gonna be almost impossible to get it dial correctly without a monitor to compare to it.
I'd be glad to fix it up for you if you need I'll make it as accurate as they get.
Jason
VetteInstruments@aol.com
Its gonna be almost impossible to get it dial correctly without a monitor to compare to it.
I'd be glad to fix it up for you if you need I'll make it as accurate as they get.
Jason
VetteInstruments@aol.com
