Decided to take the plunge and fix the non working tack on my 76 and convert the dash bulbs to led while I was at. Problem is, I replaced the circuit board and checked all my connections before I installed it back, which all showed to be good [good ground, good 12v, proper continuity to distributor tachometer output] NOTHING. I pulled it out and just did a ground and 12v test straight to the input spade connectors and the needle doesn't budge. Any help would be greatly appreciated. I am assuming at this point it has to be in needle housing, but wanted to get some others input before I spring for one.

 

You should do a zero set on the board before installation, this would also tell you if the movement was working or not.

If you power up the tach without the needle on it it, it should go to zero, then set the needle in place.

Then without power move the needle and to say 2k, then power it back up again. If it doesn't go to zero then I'd try to back off the nuts holding the board to the movement a tiny bit, and then re-tighten them. If you still don't have any movement then the analog movement is dead.

If you can ship me the tach I can put it on my tester here and tell you if it's a board problem or movement issue. Also, where did you get the board? If it's mine it'll have my name on it. If it's one of the two variety import boards then that could also be the issue. Some major vendors stopped buying the import boards due to issues and only carry mine.

I did a video on how to zero set the needle and one other issue is when people pull the needle off the tach, sometimes the needle will pull out and stick in the housing. So before I do a zero set I always push the spindle inward with the back side of my fingernail.

Willcox

 

Thank you Willcox, got it!

 

My pleasure

 

How long did it take you to get the tach out of the dash? I am contemplating doing the same thing on my '75 depending on how big of a pain it is.

 

It probably took me close to an hour and if I had to do another, I could probably do it in 30 minutes now. On the PITA scale 1 being easy and 10 being it doesn't get any worse, I would say 4. If you kick the window out, it could go much faster

 

After endless problems with my speedo (I hate repro speedos) I'm down to 15 minutes flat for taking the dash out and 30 minutes to put it back together.

Some tips (mine is a 71, should be mostly the same until 78).:

Remove the steering wheel and lower the column. No need to remove the column from the car, just remove the 2 bolts holding it up and loosen the 2 nuts on the firewall.

Don't forget to remove the turn signal and tilt levers.

Put masking tape on the jamb close to the headlight switch to prevent it from shorting as you pull the dash unless you disconnect the battery.

While you have the dash out you can consider putting all electrical connections in a multi-connector as that will make life much easier if you ever have to remove it again.

 

I already have the seats out and the steering wheel off as part of the interior work I am doing so it seems I have no excuse to not do this. I had the whole dash out of my '69 over 20 years ago and have few memories of exactly how to do it, but a general bad taste in my mouth from it.

 

NEW INFORMATION!!!:

The tach is at 700 rpm when the car is turned off, I assume that means the tach is fubar, but I just realized the little capacitor thing that was mounted on the intake (it was not connected to the wire harness, that wire had broken, it was that way when I bought it in the spring) is the tach filter. My guess is that replacing and correctly hooking up the tach filter will not fix my issue, but I will have to replace that as well, correct?

Thanks,

Scott

 

Your tach can read anything when the key is off. With the key on, engine off, it should read zero.

 

 

yup
mine settles at 1k. done that since day 1

 

I have started the removal, got the steering column down and everything from the front unscrewed. What else needs to be disconnected from the back, the speedometer cable, what other cables / wires are there?

 

Headlight switch needs to be disconnected. Pull **** out, press release button and remove ****. Unscrew retaining nut.

 

Thanks, it is out! I was able to just disconnect the wires from the switch assembly once I got it pulled forward a bit. The speedo cable required some fiddling with that clip before it would let go. The dash has been out before and I knew the surround for the tach was broken, so I will be getting that along with the circuit board.

 

Fun, isn't it.

I just put my dash back together this morning. I really hope it's done this time.

 

 

Fellow Corvette Forum Members (and Ernie in particular),

I have received my rebuilt tach from Willcox, when I opened the box the needle was at about 2500 rpm. I set it back to zero and installed it in the gauge cluster and put it in the car. Somewhere along the line it got bumped to about -300 rpm, I noticed it as I was putting in the dash. I got it all hooked up to test the lights and started up the car and it went up to the correct RPM and when I shut it off it went back below 0, perhaps not as far below as before, however. Will this thing re-zero itself or do I have to pop it off and set it to 0 and then hope it does not get bumped when I am putting the dash back in?

Thanks, Scott



I confirmed the engine is not spinning in reverse at 200 rpm, so the gauge is incorrect. Note the nice bright new LED bulbs.

 

The procedure to zero the tach is, with the tach connected to power and ground, install the needle at zero. If you installed the needle at zero with it not powered up, then that is the problem. Again, as stated in previous posts, the tach can read anything with no power(key off), but should be at zero with key on, engine not running.

 

Awe Scott...

The tach was ready to install....

On a factory tach it remembered the last setting. This was based on two things... one the tach board had memory and holds the last reading and two the oil inside the movement is not dried up. On a tach with a dried up movement you can tilt the tach back and forth and make the needle move, on a tach with a good analog movement you can't do this.. it might move a little but not much at all. Either way the tach will still usually function properly once installed if match calibrated.

I match calibrated your tach board to the movement so it was ready to install without any adjustment. When you install the tach and turn the key on the board will only get power and ground until you start it, so once you just turn the key on, the movement would go to zero (until started).

Now the issue... To dial a board to match the tachometer to the movement you have to pretty much have the RPMS at 4000 to be accurate.

The reason is that the board uses sine and co-sine to push and pull the needle. But at 2500 rpm's the sine which is the pusher, flips to the puller and the co-sine which is the puller, becomes the pusher...

To translate this to you a bit... minor adjustments made at say 700 rpms make huge changes at 4000 rpms... but minor changes at 4000 rpms makes tinny tiny changes at 700.

I'm afraid you don't have the equipment to re-calibrate this... so there are two choices.. Send me the tach back and I can re-dial it in for you, or I have an extra tester here.... I suppose I could ship it to you so you can tweak the tach board back in place. I'd suggest just sending me the tach back and I'll set it up again would be the easiest.

Ernie