hattmuber

My tach is off about 1000 rpm does any one know how to correct it?

klause83z28

About the only way to fix that is to either get a new tach or get the old one restored. www.autoinstruments.com will restore the one you have, but with the price of used ones why restore?



Cheers!!!!

stoned_pimp420

autometer is our friend

hattmuber

well,see the thing is that it was accurate until I switched motor, trans and rear end rearend I got my speedo back to accuracy, just thought maybe there was a way to recalibrat the tach or sumpin, as I do not want ANY obvious aftermarket products on my car,check out my V.B. garage and youll see the goal Im after thank guys!

firehawk71

I have same problem with my 91 Z28 the tach reads WAY high when you just touch the gas it shoots way up. Everything is factory stock on my car

John in RI

iTrader: (167)

If your car was a V6 and you swapped a V8 into it than you need to swap the cluster too. The easiest way to tell what cluster you have is to look at the Oil pressure gauge.... V6 = 40/80 and V8 = 30/60.

If you want to retain the original cluster to show the CARS mileage after an engine conversion than you can always buy a signal converter from Digital Dakota to convert the V8 distributor signal to the V6 tachometer.

firehawk71

Any ideas what might be the cause of my tach problem. At idle it reads just a little high but when you rev it to guessing about 3000 rpm the tach shoots up to 5000 rpm almost redlines and engine is nowhere close to that. Every thing is factory stock. I hate to tear the tach out if there might be something easyer to try first like a sender? or something..Any ideas?
Thanks

BigBadLou

iTrader: (3)

See, the problem is in the driver board that drives the tachometer gauge itself. It uses precision ground resistor chips that slowly change value over time. That way, it's hard to notice the change until it's 1000rpm off or so.

On the older tachs (pre-1990), it is usually a capacitor that's at fault and replacing it fixes the problem most of the time. On our 1990+ tachometers, the resistors need to be replaced and recalibrated precisely with a function generator. Not an easy job. But it can be done.

If you feel like tackling the job yourself, search this forum, you'll find a thread or two with answers.

I have exactly the same problem - I know what's wrong, I know how to fix it, I know I CAN fix it. But I just don't have the time. Once I fix mine, I'm thinking I could offer to fix others' tachometers as well. But that's in the future.

Lou

firehawk71

Hey Lou, Thanks for the info, Sounds like its in the tach itself then. Can I ask if I wanted to remove the tach to get fixed or replace it how hard is it to get the cluster out. Dont suppose there is a way to remove the tach without taking the whole cluster out? I can wish right?

BigBadLou

iTrader: (3)

Yes, you can wish.
The cluster is non-separable. You need to remove a few trim screws and pull the trim around the cluster. Then the cluster itself is held in by four screws. Once those are out, gently wiggle the whole thing out. Tilt your steering wheel all the way down, it helps.

If you're taking the cluster to somebody to fix it, give them this connector pinout and a diagram, it will help them a lot.
http://www.austinthirdgen.org/mkport...ter_pinout.jpg
http://www.austinthirdgen.org/mkport...uges_part4.gif

Lou

Jza

To expand a bit, the resistor mentioned above is part of sort of a resistor pack (basically several resistors in a "chip" looking thing). I've seen fixes where the person has actually severed the continuity across the resistor, and soldered in a resistor closer to the original value (or whatever value actually "calibrates" the tach). It's sort of trial-and-error, but looks like an easy DIY repair as far as the actual execution of it. Search around, or if I come across it in my bookmarks I'll post back here.
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Here's a helpful thread:

https://www.thirdgen.org/forums/elec...meter-fix.html

firehawk71

Thanks to everyone for your input on this tach problem. Since this is a problem resistor I would assume it is on some sort of a circut board. Is it possible to just swap out the whole circut board from another tach instead of trying to fix the bad resister? Thanks