How in the hell do you re-calibrate the tachometer? - Third Generation F-Body Message Boards

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How in the hell do you re-calibrate the tachometer?

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Old 12-22-2004, 01:23 AM   #1
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How in the hell do you re-calibrate the tachometer?

I just scored a 90-92 145 mph speedo and installed it and the damn tach was idling at 6000. So I took the glass off and moved the needle and it idles at 1000 (grrrr). I couldn't get this sucker to stay at 800 for crap. Not only that but when I rev it seems to move double the distance. at 3200 rpm (verified through datamaster) this thing is already past 6000. How in the hell can I re-calibrate it? Thanks.
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Old 12-22-2004, 02:27 AM   #2
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YOU can't. There are some places that will repair/recalibrate it, prices range from $85-$125.
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Old 12-22-2004, 06:09 AM   #3
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I saved this thread when I bought a 6 cyl cluster ,(not knowing the difference)..It might help
I'm not to slick on posting,so try cut/paste
hope that helps
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Old 12-22-2004, 09:46 AM   #4
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That thread is about the older tachs. The newer 90-92 instrument cluster has different gauges and uses a bit different technology.

The tach is calibrated by precision cut resistor module that's soldered onto the driver module board in the instrument cluster box right below the tach.

It is not easy to adjust but if one has access to the right equipment (Fgen, meters, scope, parts), it's not impossible. I myself am thinking about adjusting mine (got sold a dud that shows way off) but can't find the time. If I succeed, I might offer this service to fellow 3rdgenners.

Hope this helps.
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Old 12-23-2004, 02:45 PM   #5
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Bad Capacitors?

I think it is likely that a capacitor has gone out of tolerance like the specified link talks about replacing. If you're handy with a soldering iron it would be quite cheap to replace all the capacitors on the circuit board with new ones.

Certain capacitors lose their value over time and this could easily cause the tach to go way off.
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Old 12-23-2004, 09:32 PM   #6
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pasky, does the tach board you have look like the 1 from the other thread or this 1?
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How in the hell do you re-calibrate the tachometer?-tachboard.gif  
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Old 12-27-2004, 12:57 PM   #7
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I have a friend that works in an instrumentation/calibration lab where I work verify the accuracy of my factory tach (also had him do some other tachs I have). Basically you just hook the tach up to a piece of equipment called a signal (frequency, pulse) generator, determine your pulses per rev, and set the machine at a specific rpm, and verify if the tach is reading the same. We did mine in 200 rpm increments, and it was amazingly accurate up to 6000 rpm - after that, it read about 200 rpm low up through 7000. Since it was overall pretty close, I decided not to try and recal it.
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Old 12-31-2004, 07:32 PM   #8
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Try This

I work on electronic equipment at work a lot. I have not experienced the problem you describe but I would suggest that the first thing you should probably do is be dang sure that the contacts on both the cluster and the car are clean. What you describe could be the result of the tach getting erroneous signals through bad contact... Sometimes those contacts look clean but there is some accumulation of oil.dust etc that is just bad enough to cause a poor contact.

Worth a try before you spend any money...

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