I bought a new old stock tach and had it put in today. The mechanic said it reads the same as my old one - way too high (+/- 2500 at idle). The new tach is identical to the original and looks absolutely new. The mechanic seems perplexed. Could it be another issue thats causing the misread or did I just buy a defective one?

This is the tach I bought:

http://cgi.ebay.com/ebaymotors/NOS-8...4506.m20.l1116

 

The odds of 2 tachs having the same problem.. well, it's more likely the tach isn't the problem.

 

yea but our tachs are known for doing exactly that, i have had 2 that did the same thing


IIRC its just a resistor you got to swap out, if thats the case west i can fix it for you, just give me or the b'man the tach and i can soder a new resistor or whatever in it, but we would have to have someone on here tell me what to replace

 

Thanks for the offer Jason, but what gets me is the tachs have a history of working well for many years before they wack out - my original tach was 12 > 14 yo before it did.

 

yea........a resistor can burn out after a few years if thats really what causes it read wrong, ill be watching the fourm, if there is a way to fix one of your 2 more than likely i will be able to do it

 

Mine did the same thing... but after an engine swap.

my Aftermarket one is Zip Tied to the stearing wheel and is working like a champ.
lemmen know if you figure it out, I have a spare 84 that may become a road racer.

 

The mechanic thinks the tack is ok. He feels that there may be a wire insulation problem that allows static electricity to increase the RPM read. At idle the tach reads 2500 (250% above normal) but the greater the true engine rpm the more off the tach reads. It sounds plausible to me - your thoughts?

 

found out some stuff

make sure your connections are good on the dizzy and where the tach plugs into the cluster

your can be fixed, but it would prob take an afternoon and the car would have to be on hand to "tune" the tach

or http://www.bobsspeedometer.com/ can repair

the best that i gathered is its very common to happen to our tachs and that its the tachs themselfs

 

The new tach you have is to a v6 that is why is does not read correctly. You can tell this because the oil pressure gauge is to 80 psi. Also because a 6k red line is to a v6

 

https://www.thirdgen.org/forums/elec...ach-fixed.html


BINGO!!!!!!!!!!!!!!!!!!!!

bring me your tach and i will fix it
you could also give it to the b'man and have him give it to me......looks like i may be fixin his now, his is starting to go funky to

 

Ya, I'm betting that it's the printed circuit board and not the tach itself. It's a quick fix, I had another member fix mine for me, because I am uncomfortable working on printed circuit boards. But my tach is dead on now.

 

HOLY CRAP - It even says so on the ebay link I posted. Wish I has the sense to read the damn stuff before I bought it. The link says it can be changed to an 8 cyl at a clock, speedo or tach shop. What the hell would they do to it?

I'm an effin idiot.