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chris2323

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On my '97 the tach is accurate, but the air core motor for the speedometer was causing it to read 15-20% high. I tried 3 replacement instrument panels before I got one that only reads 10% high. I discovered the tach air core motor has the same number as the speedometer one, BUT the plastic "locator" feet are oriented backwards. I trimmed them and it will fit, but at that stage I didn't want to take mine out of the truck again to try it. I kept it for when this one starts reading higher again.

Also, the pre-95 or 96 (not sure which - have a different sensor setup than the newer ones. VSS? Not sure...
Im starting to think i got some bad instrument panels from the salvage yard. Maybe i will try to find some replacement air core motors, or save up and go with dakota digital. Is there any way to test the air core motors, confirm they are bad?
 
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slovcan

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Im starting to think i got 3 instrument panels from the salvage yard. Maybe i will try to find some replacement air core motors, or save up and go full digital.

OK, a couple of things. Someone mentioned V6 versus V8. I will add diesel clusters won't work for you, either. Do you KNOW what those three replacement clusters came out of? The speedometer and tach had different ranges sometimes, too. Get as close a match as you can.

The tach error really is weird. Most people get the speedometer error and that happens to practically all of them. That's why it's hard to find good ones at junkyards. Yours is the first I've heard of the tach error.

Tell us the history of your truck. How old, how many miles? Are you sure? How long have you had her? Have these errors been there all the while you've had her or did they progress to this stage? Is it possible someone before you changed some things out?

My theory on using the tach air core motor is that the tach motor will do exponentially less work during its life than the speedometer. It will live in the first 30% or less of its scale and fluctuate less than the speedometer, therefore ought to go way longer than the speedometer ones before going out of whack.
 

chris2323

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OK, a couple of things. Someone mentioned V6 versus V8. I will add diesel clusters won't work for you, either. Do you KNOW what those three replacement clusters came out of? The speedometer and tach had different ranges sometimes, too. Get as close a match as you can.

The tach error really is weird. Most people get the speedometer error and that happens to practically all of them. That's why it's hard to find good ones at junkyards. Yours is the first I've heard of the tach error.

Tell us the history of your truck. How old, how many miles? Are you sure? How long have you had her? Have these errors been there all the while you've had her or did they progress to this stage? Is it possible someone before you changed some things out?

My theory on using the tach air core motor is that the tach motor will do exponentially less work during its life than the speedometer. It will live in the first 30% or less of its scale and fluctuate less than the speedometer, therefore ought to go way longer than the speedometer ones before going out of whack.
My truck is a 97 Z71 k1500 5.7 l31, 4l60e 4x4, 411pcm, 360,000miles. First 2 clusters i tried came from 97 models with the same engine. One cluster was from a 95 v8. I checked my RPO codes in the glovebox and they line up with my current engine, trans, gear ratio. Ive had the vehicle for 10years and i think the rpm/mph gauges were accurate when i got it, but im not certain. They have been off for a very long time. Also, my fuel gauge has always bounced around when I accelerate or hit the brakes. Almost like fuel is moving around in the tank. Even after replacing the fuel pump(for other reasons) it still does it.
 
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sewlow

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My theory on using the tach air core motor is that the tach motor will do exponentially less work during its life than the speedometer. It will live in the first 30% or less of its scale and fluctuate less than the speedometer, therefore ought to go way longer than the speedometer ones before going out of whack.
Not so with any vehicle that I've ever owned.
The tach needle, especially in those with a stickshift, has always been w-a-y more active than the speedo's needle.
That tach needle is sweeping up through each gear, (not necessarily to redline) 4x (auto) or 5x (stick) while the speedo is only making one single sweep when accelerating up to speed.

~ A redline a day keeps the carbon away. ~
 

slovcan

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Not so with any vehicle that I've ever owned.
The tach needle, especially in those with a stickshift, has always been w-a-y more active than the speedo's needle.
That tach needle is sweeping up through each gear, (not necessarily to redline) 4x (auto) or 5x (stick) while the speedo is only making one single sweep when accelerating up to speed.

~ A redline a day keeps the carbon away. ~

:) you'd be bored driving with me! 4L80E shifts around 2000 RPM. Stays around there or under unless I get on the highway where it sits around 2300-2500. Oh, I DO punch it sometimes. How can I not with the 454 and Black Bear PCM? I agree with you on the manual bit, though. My Maxima is a 6-speed manual.
 

ralmo94

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:) you'd be bored driving with me! 4L80E shifts around 2000 RPM. Stays around there or under unless I get on the highway where it sits around 2300-2500. Oh, I DO punch it sometimes. How can I not with the 454 and Black Bear PCM? I agree with you on the manual bit, though. My Maxima is a 6-speed manual.
Yeah with a big block you don't have to rev much when just driving around. My 5 speed Honda uses the whole tach range most of the time just to keep up with traffic. Lol
 

HotWheelsBurban

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Not so with any vehicle that I've ever owned.
The tach needle, especially in those with a stickshift, has always been w-a-y more active than the speedo's needle.
That tach needle is sweeping up through each gear, (not necessarily to redline) 4x (auto) or 5x (stick) while the speedo is only making one single sweep when accelerating up to speed.

~ A redline a day keeps the carbon away. ~
Blow out the cobwebs....
 

slovcan

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My truck is a 97 Z71 k1500 5.7 l31, 4l60e 4x4, 411pcm, 360,000miles. First 2 clusters i tried came from 97 models with the same engine. One cluster was from a 95 v8. I checked my RPO codes in the glovebox and they line up with my current engine, trans, gear ratio. Ive had the vehicle for 10years and i think the rpm/mph gauges were accurate when i got it, but im not certain. They have been off for a very long time. Also, my fuel gauge has always bounced around when I accelerate or hit the brakes. Almost like fuel is moving around in the tank. Even after replacing the fuel pump(for other reasons) it still does it.

Thanks for clarifying your truck's details and history. Sounds to me like old age and higher mileage got to your speedometer's air core motor. To me your tach is a mystery unless it has also succumbed to the age/mileage. Actually, yeah, I suspect that's exactly what it is considering it has 576,000 kms on it - about double what mine has.

Now, your fuel gauge - mine is just starting to do that in the past year. THAT is apparently a pretty easy fix. I've seen it on youtube. You need to inject some light oil (sewing machine, shaver, etc.?) down through the needle shaft of the gauge's air core motor and hey presto, no more bump bounce boogie.
 
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