4.3 vs 5.7 gauge cluster

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DanG

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i replaced a 4.3 5speed with a 5.7 5 speed in my '91 silverado; needle style gauges, and now speedo and tach are way off, i was told that the v6 and v8 gauges are different; is this true and if so, how to tell difference? learning as i go, thanks for the help
 

DerekTheGreat

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Did you also swap the trans too? I can understand why the tach would be off but the speedometer is driven by sending unit in the trans, that shouldn't change unless the speedo gears also changed.

Oh, props to having the unicorn needle cluster. I hoard those.
 

someotherguy

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1988-1991 the calibration for the speedometer is done inside the cluster, there is no external DRAC. So the only way you could swap clusters and have the speedo still be correct by default is if the donor truck had the same rear gearing and original tire size as your truck - the odds are not in your favor.

It's not hard to calibrate those clusters, just a little more work than the 1992-1995 with their external DRAC.

I did a write-up on it, with pics, it's for a moonie cluster but the process is the same: http://www.chevytalk.org/fusionbb/showtopic.php?tid/258562

On the tach it's because of what you already know: v6 vs. v8. Since the tach signal comes from the distributor, the reading will be wrong. From what I've read a few times, there may be something as simple as changing a resistor on the cluster but dammit if I can't find the original article that talked about it - it's kind of a rare topic since not many find the 1991 needle cluster and then need to fix the tach reading. :/

Richard
 

DanG

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Did you also swap the trans too? I can understand why the tach would be off but the speedometer is driven by sending unit in the trans, that shouldn't change unless the speedo gears also changed.

Oh, props to having the unicorn needle cluster. I hoard those.
Thanks for the comment; i did swap out trans with motor but rear gear and tire size may explain the issue. Also lowered slightly (2/4) but don't think this would affect speedo
 

DanG

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1988-1991 the calibration for the speedometer is done inside the cluster, there is no external DRAC. So the only way you could swap clusters and have the speedo still be correct by default is if the donor truck had the same rear gearing and original tire size as your truck - the odds are not in your favor.

It's not hard to calibrate those clusters, just a little more work than the 1992-1995 with their external DRAC.

I did a write-up on it, with pics, it's for a moonie cluster but the process is the same: http://www.chevytalk.org/fusionbb/showtopic.php?tid/258562

On the tach it's because of what you already know: v6 vs. v8. Since the tach signal comes from the distributor, the reading will be wrong. From what I've read a few times, there may be something as simple as changing a resistor on the cluster but dammit if I can't find the original article that talked about it - it's kind of a rare topic since not many find the 1991 needle cluster and then need to fix the tach reading. :/

Richard
Thanks for the info. i'll be happy if i can get the speedo "close" to correct and add an aftermarket tach
 

DerekTheGreat

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Well yeah, if it's the same type of trans (not sure if all speedo gears are interchangeable) then just change the gears over. You might only need to change the "driven" gear if both utilize the same drive gear. In both cases of my cluster swappage, I got extremely lucky as the cluster was set up for my tire size and gear ratios. SOG's post is awesome because it shows you what combinations will work in order to get your speedo right. It's the same info I used to determine I didn't need to change my calibration at all.. Your truck may already be set-up for what you're doing minus the speedometer gears.
 

someotherguy

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This is not a transmission speedometer gear issue. You're thinking in terms of cable drive speedometers. These electronic speedometer transmissions do not have a drive gear/driven gear combination like a cable speedo trans. They have a reluctor ring and an electronic sensor, these are the same parts regardless of speedometer calibration.

It's purely that the 88-91 cluster is calibrated internally based on original axle ratio and tire size, whereas 92-95 are done in the external DRAC module. So when you change cluster in an 88-91 you almost always have to recalibrate, and it's done inside the cluster as I detailed.

Richard
 

DerekTheGreat

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Oh yeah, you're right about that. I should know that considering a put a sensor in our '88 with it's dump truck SM465. Do 700R4's still use gears? I had mine changed out when I swapped rear gears in my '89 Firebird but that too is electronic. I've never been into my F body as much as these or Ford trucks though. I've only had it's cluster out to change light bulbs.

Dan didn't change clusters or did he? Doesn't state that in any of his posts so it's odd he has an issue now.
 

someotherguy

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Oh yeah, you're right about that. I should know that considering a put a sensor in our '88 with it's dump truck SM465. Do 700R4's still use gears? I had mine changed out when I swapped rear gears in my '89 Firebird but that too is electronic. I've never been into my F body as much as these or Ford trucks though. I've only had it's cluster out to change light bulbs.

Dan didn't change clusters or did he? Doesn't state that in any of his posts so it's odd he has an issue now.
700R4 could be electronic senor OR gear-driven depending on the application. If it's from a GMT400 truck it's electronic, no gears. Some other applications were a cable drive that operated a sort of DRAC in the cluster that still controlled an electronic speedometer. There are sensors that are a hybrid type unit with both a cable output and a VSS together.

You're right about OP though and in my haste of looking at other replies, I mis-read his post! I thought he did a cluster swap between a V6 and a V8 truck, using a 1991 cluster. The tach issue is due to the cylinder # difference regardless, but I had wrongly believed he brought the cluster over from another truck, which would explain the speedometer issue.

Now that I've re-read, that speedometer issue really has me wondering. DanG, what exact transmission did you remove, and what exact transmission did you put in?

Richard
 

DanG

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700R4 could be electronic senor OR gear-driven depending on the application. If it's from a GMT400 truck it's electronic, no gears. Some other applications were a cable drive that operated a sort of DRAC in the cluster that still controlled an electronic speedometer. There are sensors that are a hybrid type unit with both a cable output and a VSS together.

You're right about OP though and in my haste of looking at other replies, I mis-read his post! I thought he did a cluster swap between a V6 and a V8 truck, using a 1991 cluster. The tach issue is due to the cylinder # difference regardless, but I had wrongly believed he brought the cluster over from another truck, which would explain the speedometer issue.

Now that I've re-read, that speedometer issue really has me wondering. DanG, what exact transmission did you remove, and what exact transmission did you put in?

Richard
I put a 92 5 speed manual trans in (don't know code for it) 700R4 automatic? Truck originally had 4.3 with manual trans but was already gone when I got truck. I left cluster in that came with truck as the pin interface from my 92 was different
 
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