# Convert electronic Speedo to mechanical?



## tburch1 (Mar 26, 2012)

I took my '97 Ranger Ev 5speed out for a test drive today and everything seems to be working o.k. except for the speedometer. Discovered that it is an electronic speedo. Do I have to convert this to a mechanical version or will it work without an engine?


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## coulombKid (Jan 10, 2009)

tburch1 said:


> I took my '97 Ranger Ev 5speed out for a test drive today and everything seems to be working o.k. except for the speedometer. Discovered that it is an electronic speedo. Do I have to convert this to a mechanical version or will it work without an engine?


Most electronic speedos read a tone ring on the transmission output shaft and send the signal to your ECM and or dash module via serial communications. When hypermile-ing my Toyota I coast the last 1/8 mile to a red light with the engine, ignition, injection, power steering, and alternator shut off. With the key in the accessory position the odometer and speedo don't read/update but the radio still works. With the engine dead I switch to run position about 100 feet out and the speedo and odometer spring to life even though the "run engine" rungs of the ECM code are being bypassed on each scan. Ford, of course, could be quite different. Try my experiment on a known unmodified Ford to rule out just a hall effect sensor being unplugged on your conversion.


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## DJBecker (Nov 3, 2010)

You really need to know the specific speed sensor configuration before recommending an approach.

Some sensors are part of the transmission, some are at the transmission output shaft, some are on the driveshaft. A few are driven off of a wheel, and lmost all BMWs have a slotted magnetic interrupter on the differential ring gear. The latter approaches make the speedomenter independent of the final drive ratio.

Most automatic transmissions are computer controlled, and have internal speed sensors to make shift decisions. These could potentially be used as the primary vehicle speed sensor, but generally are not.


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## Guest (Mar 26, 2012)

Ever consider a GPS Speedo?


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## coulombKid (Jan 10, 2009)

DJBecker said:


> You really need to know the specific speed sensor configuration before recommending an approach.
> 
> Some sensors are part of the transmission, some are at the transmission output shaft, some are on the driveshaft. A few are driven off of a wheel, and lmost all BMWs have a slotted magnetic interrupter on the differential ring gear. The latter approaches make the speedomenter independent of the final drive ratio.
> 
> Most automatic transmissions are computer controlled, and have internal speed sensors to make shift decisions. These could potentially be used as the primary vehicle speed sensor, but generally are not.


 It is logical that, given the extreme cash expense of EV conversion, the right answer would be down load the factory manual, pay the fee, and study the system. When I worked for Ford that would have been the first step. After the rich got richer and the poor got poorer we check the cheapest things first down here in dogpatch USA.


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## tburch1 (Mar 26, 2012)

where can I find a reliable gps speedo? any recommendations?


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## PTCruisin (Nov 19, 2009)

tburch1 said:


> where can I find a reliable gps speedo? any recommendations?



I would think any GPS device for an automobile would report speed. I used a cheap ($99) TomTom GPS for a speedometer until I got the the Cycle Analyst hooked up.


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## piotrsko (Dec 9, 2007)

how are you going to increment the display for mileage? Last I heard that was a no-no to modify.

comments: did the speedo swing from 0 to max then back to 0 on start-up? then it is computer driven and is adapting is slightly more complex. otherwise it is a simple air core display and needs to run on 5vdc pulsed source that is either pulse-width modulated or duty cycle modulated. Is the PCM harness still there and could you re-install the computer? easiest and fastest way to fix problem. if you remove the display lights from the dash, no-body will care if it sets DTC's.


you could also find the sensor and build a divide by network ( 1 chip) to drive the speedo electronics, unless you want a digital dash from another maker.


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## tburch1 (Mar 26, 2012)

I do not understand what you mean by "increment the display for mileage? I don't really care about an odometer. It is a 15y.o. vehicle so its mileage exempt anyway.

Speedo didn't budge. Checked the fuse, but I haven't checked the VSS yet.
I don't know about the PCM, I think I mounted the pot box over it and you lost me after that.


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## DJBecker (Nov 3, 2010)

A few seconds with Google found post #4 in this thread:

http://www.ranger-forums.com/showthread.php?t=121727

How does that match with what is on your vehicle?


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## tburch1 (Mar 26, 2012)

The thread you mentioned (quoted below) give me a few other things to check, but doesn't tell me if the PCM is required for the speedo to work. I have a '97 2wd. 5spd
I'll check it tonight and with keep my fingers crossed for something simple like a bad ground wire.

"The ABS sensor on the diff does double duty as a VSS for speedometer input in 98~00 Ranger and 01 2.5L Ranger. Other years use this sensor for ABS only.

The 95~97 speedometer gets its signal directly from a gear driven Signal Generator. The 2WD SG is driven from the transmission; the 4x4 SG is near the top of the transfer case. 

The SG uses two wires. The gray/black goes to the speedometer, PCM and speed control in parallel. The pink/orange goes to the bolted ground under the hood on the DS inner fender apron.

Possible causes for dead speedometer:

Open/grounded gr/bk wire 
Open pk/or from SG to DS inner fender apron ground point 
Bad speedo head/cluster
Bad Signal Generator
Stripped drive gear for SG"


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## tburch1 (Mar 26, 2012)

I got rid of the PCM during the conversion. Stupid? perhaps, but I was told by others with experience that I didn't need it. Of course their vehicles are older so for them it was o.k. So should I try to get a new PCM and hook it back up? Or does the speedo gauge get its signal direct from the VSS with out going to the PCM. If so I could simply bypass the PCM?

Thanks


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## mizlplix (May 1, 2011)

Look on the left/rear of the transmission on the tail extension housing. Is there a plug-in module with a wiring connector?

If yes, this is the VSS. it usually operates the speedo directly.

If no, the rear ABS sensor doubles for the VSS and chances are it makes an AC signal which needs converted to DC to be used on the speedo.

Good info. here.http://rechargecar.com/product/warptm-speed-sensor

I used one for my tach, but you can use the sensor on the output yoke for your speedo. Just find out how many pulses it needs per revolution. Make a tome wheel to suit.

Miz


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## etischer (Jun 16, 2008)

On my VW the speed sensor goes to the ECU, then the ECU sends the signal out to the speedometer. I removed my ECU, but was able to hook up the speed sensor directly to the speedometer and it works, even the odometer. My tach was more difficult, but it may also be a solution for you. I cut the circuit board traces on the speedometer and hooked up an arduino to drive the needle.


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## tburch1 (Mar 26, 2012)

Yes it is a VSS on the trans. So now I just have to figure out how to wire it directly to the gauge. Any hints here?


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## mizlplix (May 1, 2011)

If it is two wire ......run them up to back of dash panel. One to panel ground....one to speedo input. Reverse wires if still not working. 

If still not working...several converters are available online. Google it.

Gluck...Miz


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## tburch1 (Mar 26, 2012)

I think I've got this figured out. The wires from the VSS on the trans. go to the PCM and ground. From what I've read this signal is not altered at the PCM and since I trashed the PCM I can try to just connect this wire directly to the wire coming from the gauge. With any luck I'll have a working speedo. I've removed the instrument cluster identified and traced the corresponding wires so stay tuned....


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