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Discussion Starter · #1 ·
Has anyone here ever tried an electric speedo conversion?

I am doing an LS1 conversion on my 79. Getting a cable converter box or having the tailshaft of my 4L60E modified for a cable driven speedometer seems like spending money to go backwards, so here's the plan....

I don't like the look of aftermarket gauges in this car, so I'm disassembling the OEM 140MPH speedometer and replacing the cable driven hardware with an Electric driver from a modern vehicle while still maintaining the OEM look/feel for the Corvette.

I've pretty much completed the conversion - it will be a while before I can test/tune the setup because I still haven't dropped in the engine (that's next).

Here are a few pics of my pretty much completed conversion







 

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Looks like a stepper motor. How do you know the sweep is going to match the 'Vette speedo sweep? what drives it? I'm going to imagine that it's driven by a square wave or 'pulse' with a sensor and magnet on the drive shaft? It may not be very configurable w/o some electronic hacking. do you have access to a bench signal generator?

With a signal generator, you could pretty much dial it in, if you can mod it at all. All you would need to know was your rear end ratio and outside diameter of your tires, and do some simple math.
 

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Discussion Starter · #4 ·
Looks like a stepper motor. How do you know the sweep is going to match the 'Vette speedo sweep? what drives it? I'm going to imagine that it's driven by a square wave or 'pulse' with a sensor and magnet on the drive shaft? It may not be very configurable w/o some electronic hacking. do you have access to a bench signal generator?

With a signal generator, you could pretty much dial it in, if you can mod it at all. All you would need to know was your rear end ratio and outside diameter of your tires, and do some simple math.
It is a stepper. The onboard circuitry drives the stepper & handles the micro stepping, all I have to do is feed it a 5v square wave signal.

My 4L60E outputs a speed signal to the ECM, the ECM then has a speedometer output that is tunable via software. From the research I've done so far, it appears the output signal is square and 5v.

I will be tuning the LS1 myself, and while I'm doing so, I should be able to tune the speedometer output signal to dial it in to exactly what I need.

If a person were doing this to a car without an ECM or who couldn't program their ECM, Dakota Digital makes a calibration box that would likely allow them to dial the signal in to what they needed.

If it turns out that I can't make the LS1 ECM output exactly what I need, I'll either verify the Dakota Digital calibration box will, or I'll build a custom micro-controller to do the conversion for me.

The original (donor) speedometer needed approx a 1 pulse per sec per mile/hr and had a very similar sweep, so my required signal should be close to that. My "test bench" right now is another car that was similar to the donor & an oscilloscope. I may build a "real" test bench setup as I have plenty of time before I'll be able to do any in-car testing. I plan on doing the final verification (and adjustment) via GPS to make sure I nail it.

Only big problem in doing this for some is that if you notice, I no longer have an odometer. It doesn't really matter for this car because the original was not accurate and no one knows the real mileage on this car (neither myself, or the govt), and it will be tagged with "Historic Vehicle" tags which exempt it from state inspections or annual registration.

I may do an electronic odometer setup. I have a lot neat plans for modernizing this car - but my primary focus for now will shift to getting the engine/trans in and running so I might be able to drive it a little this summer.
 

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Nice looking work. I like the idea of the electric conversion as I have done most of mine also with the stock faces for my LS conversion. The only one I have not done is the speedo but I do not think I can do it with my setup. My TKO does not have an electric output from it. I am still cable driven at this point. I did however recently go into my speedo and refresh it so that it does work. Looking forward to seeing how you handle the odometer issue. I think it would be pretty cool to have some digital numbers back there kind of like the late model Chevy trucks or something similar.
:thumbsup:
One thing I think I would do is put a little black paint on the heads of the screws, otherwise superb work.
 

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Discussion Starter · #6 ·
Yeah, those screws are pretty crusty, I'd like to find some new ones - otherwise, they'll get cleaned up and a touch of paint. The face of my tach has a small amount of surface rust in a spot too - not sure what to do about that.

If you were interested in going electric, there are speed sensors that will screw right in to the cable output off the transmission. I bought one for an old truck/TPI conversion I did about 10 years ago. In fact, they go inline so you can still have the cable, while providing the ECM with the signal it needs.

I believe mine was an OEM application from some sort of Chrysler. I think they're also used in taxi cabs. 2000 ppm. I got it from a speedo shop for about $50 - but if you know the application I'm sure you could pick one up for much less.

If I can find an LCD small and slim enough to fit in the OEM locations for the odometer & trip meter - that would be really cool. I have other ideas if I can't though....
 

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86atc250r said:
If you were interested in going electric, there are speed sensors that will screw right in to the cable output off the transmission. I bought one for an old truck/TPI conversion I did about 10 years ago. In fact, they go inline so you can still have the cable, while providing the ECM with the signal it needs.
I may have to look into that electric speedo output thing. That is supposed to help with tuning I have read also and boy do I need all the help I can get when it comes to tuning this thing.
 

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Discussion Starter · #8 ·
Small update-

Project electric speedometer is a success.

As it sat, with my LS1 ECM programmed with tire size and rear end gear, it was about 13% slow. I made the adjustment in software and have verified the speedo at about 25mph, 35mph, 60, and 70 with my GPS. It's within 1mph at those speeds so I imagine it will also be as accurate as a new car at greater speeds as well.

All in all, this is a vast improvement over the cable driven unit - especially considering the alternatives for using a 4L60E or T56 suck.

I still have not addressed the odo/trip meter issue, I'll probably tackle that this winter when I tear the inside of the car apart.

Oh yeah, I also cleaned up and painted those screws :)
 

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wiring it up

Hello i know this thread is from 2009 but i just put a t56 in my car with vss. My plan is to buy the 2000 camaro speed stepper motor but how do i wire it? It has four pins Im guessing one is a ground and the other gets the 5v. could you help
 
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