KDMullaney

Hi Guys,
I have a 1981 Corvette - the tach was not working so I purchased the Willcox replacement board. The tach started working, however is was
reading low - at 700, it was reading 400 - at 2k it was reading just
under 1k - once it hit 2k the needle started jumping and would not go
higher. Figured that maybe it was the filter so I purchased with
Willcox tach filer but it did not change how the tach operated. If I put a meter on the signal terminal behind tach my handheld gives the
correct reading. Also, when I set "0" it works perfect but then after
a few starts it needs to be re-set as it starts reading lower than "0".

Any Ideas?

Red 69

I can't say what will solve your problem, but will share my failed 79 tach experience. After changing the board with one from a vendor in my area three times, it still did not work properly. A new filter didn't help either, so I started looking for an inexpensive solution. When a working tack and circuit board came available from a parts car on this forum, I bought the set at a very reasonable price. After being installed, it worked perfectly. If buying a used tach, get the board it came with if possible. This way you know it is a system that will work without adjustment. Since you purchased the board from Wilcox, call them for a suggestion; their tech may offer a solution.

KDMullaney

My vette sat for a while so I bought a working system from a guy, but, it did not work. Thought the filter and board were the only parts that could go bad but the movement is also could be an issue. Willcox is great - they send ship the whole thing to them for diagnosis - just hate to burn the time if there was something that maybe I was missing. Now I have 2 tachs, 3 boards, 2 filters and a dashboard in pieces.

DUB

I would be taking a look at the pink gauges wire circuit and MAKE SURE that you are getting CORRECT VOLTAGE at the tach and it now 'acting up'.

Are you SURE you have a good ground????

Have you tried to take the tach out of the dash and connect wires directly to it and have it out in the engine compartment....thus taking your cars wiring 'out of the equation'??? Fairly simple circuit...a ground, fused power wire and the wire form the tach in the distributor cap.

DUB

VIETNAMVETTEOWNER

>It seems a lot of us are having the same problem. I bought replacement parts for my 1981 vette from corvettepartsworldwide.com and have already been through 2 tachs, 2 boards, and 2 filters ...and an inordinate amount of work, without solving the problem. Did you ever find out what the problem is and how to fix it?

VIETNAMVETTEOWNER

'75

I ran into an issue on a 78 where the clips that the tach studs slip into were loose and were giving an intermittent contact. Make sure those are fitting tight to the tach studs.

VIETNAMVETTEOWNER

Update ...After installing a new tach board and filter on my original tach nothing worked. When I installed a brand new tach, it worked but gave inaccurate readings, fluctuation and the needle would not return to zero when I turned the engine off, without toggling the ignition key. The parts vendor (corvettepartsworldwide.com) was no help and subsequently informed me I could not return the new board because they have a no refund policy on electrical parts. I read numerous other posts in the forum regarding this problem going back over ten years, with no viable solutions. I would appreciate hearing from anyone who knows how to fix this problem.

'75

One part of your description that is normal is that with the key off, the tach can be pointed anywhere, as long as it goes to zero with the key on.

BlackC3vette

I replaced the board in my 80, the tach was sent to zero on the work bench. All the terminals were cleaned before the reinstall and mine works fine, but I also replaced the plastic circuit board for the Speedo/Tach unit.

0Willcox Corvette

The needle isn't supposed to return to zero when you turn the key off, it actually should stay where it was when it received the last signal. The weight of the needle will pull it down some and even this is based on the condition of the spindle oil inside the actual movement.

When you installed the tach board did you do a zero set? If you didn't do the zero set that would explain the calibration being off.

Also.. there is a boat load of diagnostic help on my help and repair site at the link below.

I'm going to guess you got a cheapo china made board mainly because I don't sell my boards to the vendor above (unless he's buying it from one of my vendors). This board has a long history of issues and that might be the issue too. The potentiometer on this board is a 1 turn pot and if you flick it with your finger it will change calibration. They are easy to ID because the usually come with three red washers.

My boards have my name on them so if it's mine and your having an issue you can mail the tach with board to me and I'd be more than happy to test it for you. Matter of fact, if you want to mail the import tach and board to me I can test it for you as well but before I did that I'd read the dianostic pages on the tach and do some testing.

Willcox Corvette Repair and Installation Help WebSite.

or this will get you to the 80 tach stuff.
http://repairs.willcoxcorvette.com/?yt=1980&s=tach


1978-1982



1975-1977

Kully