cheesenr7

I have a 73 Corvette. The owner before me installed a hei distributor with out the tach drive. The previous owner also installed a electronic tach out of a 75 or 76. I am having problems getting the tach working. I bought the car with it not working. I do believe the tach is ok though. I inspected the tach board and found no burn marks. When the key is turned to the on position the needle goes to 0 as it should. I tried hooking up an ignition analyzer to the tach side of the distributor to try and use it to read rpm but it also did not read any rpms. I have to admit i have never used this analyzer before. It was given to my grandpa years ago and this is the 1st time im using it. Before I start throwing money and parts to try and fix the problem I would rather figure out what the problem is first. The car runs just fine so I am obviously getting spark from the distributor. Is it possible that the distributor is working fine but not out putting a tach signal?


Any help is apreciated

Thanks
Nick

TimAT

To confirm you're getting a tach signal, (if the car runs you probably are), use a 12v test light. Ground the lead and touch the TACH terminal on the cap with the probe. The light should blink while cranking.
Is there a tach filter in the line between the distributor and the tach?

cheesenr7

So i decided to just run to the auto parts store and pick up a cheap tach. It worked just as it should hooked up to the tach terminal on the distributor.

So i then hooked up the vette tach again. I supplied it 12v and the needle went to 0. While the cars running the needle moved below 0 to one point but did not change with rpms when i gave it throttle. Just stayed in one spot below 0. Key off and the needle returned to 0.

So do you guys think i need a whole tach or should i try a circuit board?

Thanks
Nick

cheesenr7

No there is not a tach filter

'75

Sounds like you need a new board. Check Willcox, theirs is good and you will porbably get a forum discount. Tach

johnt365

Do you have the dash out? I to take mine out 2 or 3 times during a similar conversion. If it is out, it would be easier to check the signal wire for continuity. It sounds like you have power and ground so checking the signal wire and/or running a known good bypass wire might be my next move.

Patro46

It's probably the tach board. This said, I'd go to Willcox.com. Not only are they fair priced and honest, but they have a GREAT walk through video that tells you EXACTLY what to do to verify this issue. Mine WAS the tach board, and using their steps, I was able to verify this, order a new and improved tach board (which I think is Willcox's own design BTW) and it worked like a charm. They even show you how to calibrate it in a video. Check it out. Mine also was similar to yours. I'm doing an LSx/4L60e swap, and I've had to address both the speedometer (no cable drive on a 4L60e transmission) as well as having to swap the mechanical tach out for an electronic one...only to find out the tach face font is different between 74 down and 75 up, but that's another nightmare story that was a PITA to resolve. As far as the tach filter goes, your tach will still function without it...it just cleans up the signal a tad. GO TO WILLCOX AND TAKE BACK THAT CRAPPY TACH. YOUR VETTE DESERVES BETTER!

cheesenr7

haha i didnt plan on installing the chepo tach. Just got it to eliminate the distributor as the problem.

Thanks for the help
Nick