Hi, all,

My dashboard tach in my 1980 'vette reads high, about 25% high, as in when my dash tach says 2500, the Sun super tach ll that I bought to check it against says 2000. It is linear like this all thru the rpm range, not always 500 rpm high, but about 25% high. When I swith the Sun tach to 6 cyl, it matches up pretty closely with mu dash tach. Anybody have a clue what might be going on here? I already replaced the tach filter tjhinking that might be it, but no. Does the factory tach have a 6 cyl setting, maybe? I don't kmnow, any help out there?

Scott

 

Just bumping back up to the top, I really need to know if anybody can tell me anything about this problem and how to fix it.

Scott

 

Go to Willcox Corvette (on the left) put in 1980 Repair and Install Help and type in Tach. That might help. PG.

 

Mine reads way too high too. Mine is an aftermarket conversion. Not even sure where to start.

 

Oh yeah, I have a 1980 that reads high too. I replaced the distributor shaft assembly (including the module and coil) and the tach board at the same time. I am not sure which one is the culprit, but I'm sure one is. Anyway, thanks Pete for the tip on Wilcox. I wish I knew about that years ago.

 

Don't thank me, thank Willcox. PG.

 

I don't understand.....this sends me to a page telling me how to remove and replace the tach board.....is that what you are saying? The tach board is bad?


Scott

 

I'm not sure what is wrong with your tech, just thought you might find the answer there. Someone else will give you better advise. PG.

 

If you have replaced the tach filter, then the next logical thing is to replace the tach circuit board. Unfortunately from memory they are not ajustable, you need to replace the tach board.

 

Scott

Ninty percent of the time its the tach board which is not a bad project on an 80. Access through the dash tach/speedo cluster. The board is about $50.

Many things can go bad on those boards from the 70's. The circuit paths are thin and begin to lose their continuity; components are no longer fresh and begin to fail. Check the archives and you'll find lots that has been written.

 

Just replaced my tach board last week. My tach was buried at 60 mph down the highway. Bought a board thru Willcox there is a discount for forum members 10%. Works fine now..... pretty straight forward install. While I was in there replaced tach/speedo circuit board also. Not all the lights were working in the speedo/tach housing. everything works now.

 

Scotty,

It could be the board, but guess what?

The tach boards are on backorder right now! We don't have a single board in stock for 1978-1982 cars. I'll have to post when we get new stock in.

If you pull this I can test it real easy to see if the board is the problem. But sending it in right now would not do any good since I don't have a new board to fix it with. I maybe able to repair your old board.

Willcox

 

Well, it's not an emergency or anything, so I think I'll wait till you get some boards in. Thanks for all of your help everybody, your posts didn't help me alot directly, but showed me the direction I needed to go in, and sometimes that's all you need! Thanks again,


Scott

 

ok

 

Today I pulled the trigger on Willcox making our own boards.

There is an issue with the original IC chips being discontinued and there is an issue with the non guaranteed IC chips. (They don’t work correctly). People are not aware of it but the original chip is no longer in production so what is left on the market is either x-rayed chips (Higher in cost by 150 percent) or bogus ones (again that don’t work).

In light of this, we have strongly considered installing a processor in the boards over the IC chip. I’m not sure what kind of expense we will be getting if we do pursue a board with a processor. We just scratched the surface on this today. Either way, the new boards will either have the correct IC chips in them or they will have the processor. The cheap chips have too many issues.

Currently, we manufacture a testing machine sold to shops for testing any electronic tach using a square signal input. Now we have made another test machine which will make checking each and every board for accuracy a 2 second process as simple as sitting the board on top the test machine, flipping four different switches and making any needed adjustment. This will allow us to test each and every board on the fly and regardless of which we choose to use for the brains of the board. They will function perfect and one thing is for sure... If you've seen the video we did, the current reproduction boards out performed the original GM boards in accuarcy.

In the past we were testing all the boards, but there is always a margin for human error. To test them we would install each and every board on a tach, power it up, zero set the needle and check it. This process was way too time consuming and as stated above also allowed for human error. I’m trying to eliminate the human portion of the job.. (Plus Victor gives me grief every time we have to test a batch).

Washers will be eliminated on this final product as well. The boards will be US “Assembled” too. Since as with all electronic parts, some of the pieces will have to be made in a foreign country. Nothing anyone can do about that, but we will be loading the boards here.

I understand, we have 12 boards on the way to me right now with good IC chips. When they are gone there will be a long backorder.

Anyway, Thanks for reading…

Willcox