Hi guys,

I'm a recent owner of a 1979 Corvette and in the final stages of restoration. One big problem is the tachometer.

When I put the key in and turn the ignition on (not starting the enging) I can see the tach needle jump a little but when I start the motor the needle goes all the way to 7000 RPM and stays there even after I turn off the car. I tried to manually put the needle back to zero but once I start the motor the needle goes back to 7000 and stays there?

Has anyone experienced this weird happening before?

Ken

 

My 80 had a bout of tach oddities for a while similar to what you speak of. The downside is that it righted itself and I never really figured out what might have caused it. The tach filter is in place on mine. I have the tach/speedo cluster out and after having inspected the flexible circuit board that gives power, ground and signal to the tach, and instrument bulbs, I wouldn't be surprised if that is the issue. My circuit board was peeling apart in several places. I have yet to re-install the new one but I am hoping this will fix an issue I have had with a choke light as well. I lost my blinker and high beam indicators, and this what started me on this path and I can see where a failure with this circuit board can be the cause of all sorts of anomolies.

 

Could also be a problem with the 'hard' printed circuit board on the back of the tach. Check out Willcoxcorvette and look in their help and repair section.

They have these boards at $58 IIRC.

 

Same problem in my 79...I changed the tach board & all was good...but be advised not all new tach boards are reliable...purchase it from a vendor that knows about tach boards. pm me if you like I can tell you who I bought my calibrated board from it worked excellent!

 

Dragon-

Our tach boards are made by us and carry our name on them!


Why did we make them. Inconsistencies from other boards! We would get in 20 boards that would work fine and then get in another 20 that were junk. Since we have been testing these boards before we shipped them out, it became a naissance for us to fight defective boards. It just seemed like the smart thing to do.

Our boards are pre-calibrated and tested prior to shipment and the boards are made in the USA. We also have an online video of how to properly install them. So with this, I'll tell you how to get the tach out of the car! Quick and easy! (new detailed picture instructions should be on the site in about two days).

When you are turning on the key and the tach needle is jumping, this is the tach powering up. This means you have power and ground to the tachometer. if it is moving to 7K when you start it, there is a problem with your tach board.

The tach board is easy to replace on your car and you can have the tach out of the car in about 10 minutes tops.

Remove the three top smaller screws from the speedometer/tach clear face. Remove the two side screws from this same lens.

Once you have the lens out, remove the six Allen head screws that hold the speedo/tach inner bezel. When you do this you'll see three screws holding the tach in place. Remove these screws and pull the tach toward your body. It will pull right out of the dash.

From what you have said, and with the movement on the needle you'll have power and ground and I'm sure you don't need to test these. But others might want to know..

Where the tach is mounted in the dash you'll see three clips. On the highest clip is your power, the lowest one is the signal from the distributor and the middle one is the ground. You can test for power and ground at these clips without going crazy.... Test these and then test for continuity between the lowest clip and the distributor connection before the tach filter is in place.

If you have any questions, please feel free to post again.

Here is the Forum Special Link to the board. http://willcoxcorvette.com/product_i...ducts_id=25990 and you will get an additional discount off this price if you enter the sale code DRWH3A when you check out.

Willcox Inc.

 

Ok.. I put another 2.5 hours in tonight to finish this up for you guys. I honestly believe this will help people diagnosis tach problems as well as help them in the installation of their new tach boards. http://willcoxcorvette.com/repairand...lp.php?hID=290

I will post a new thread on this!

Willcox

 

Nice work!

 

This is what I call a great and professionnal job ! Very nice !

 

Thank you...

Now I'm paying the price.... The link to the video is not working and boy... I'm tired..

 

Hey Wilcox, this looks really good and will be helpful. Maybe I missed it but I didn't see any mention of the two dash pad screws under the dash, located on each side of the steering column. I messed around for quite a while before I found those.

 

Crash... I think you are talking about the two lower column cover screws?

You don't have to remove the dash cluster to get the tach out of the car! This is a common mistake made when dealing with this gauge. What we are doing is pulling it out by leaving the housing in the car. Now if this was the speedo it would be a different issue.

Willcox Inc.

 

True. I looked at your way cool instructions and since it showed the cluster totally removed, I misfired. The screws I am talking about are next to the steering column on either side and screw directly into the housing. The tach can be removed with that left in the car as you have pointed out.

 

Say guys, what do you think.

I ended up replacing the tach board that goes behind the tachometer but nothing happens.
Even when I turn my ignition switch on the tach needle doesn't even move anymore. I tried replacing the original circuit board and nothing happens either.

Did I end up blowing up the tach mechanism all together. Has this happened to anyone before?

Thinking about it, I purchased the board from Ecklers and it had these three round gaskets but no instructions where to place them. Has anyone purchased one from Eckler's before with any success?

Ken