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Peter, several Pantera owners have used the 5" OD Autometer p/n4490 electronic speedo. Besides the obvious advantage of being able to drive EFI, calibrate the speedo for different size tires and use other electrical gadgets, the failure-prone VDO right angle drive system can be eliminated along with the 8-ft long cable drive. There is a pulse generator that screws onto the ZF output shaft. The only downside is the $220+ USD cost plus another $75 USD for the pulse generator, as the instrument fits into both early & late dashboards.
I have one of the Autometer electronic speedometers and it's great. It is being driven by a 4 "pulse"/rev generic analogue (sine wave) VSS (vehicle speed sensor) connected to a shortened speedometer cable.

Typically speedometers expect an input of 1000 rev/mile (being metric, the ZF/VDO combination may be different). So the Autometer is getting around 4000 pulses per mile which is ~222 pulses per second at 100 mph. At 100 mph (146.6 fps) with a 26" dia tire (6.8' circumference), the tire turns at 146.6/6.8 = 21.6 rev/sec. With 4 magnets you get 86.4 pps at 100 mph. Apparently this works just fine as Autometer makes a sensor for just your application: https://www.amazon.com/Auto-Me...gnetic/dp/B005F7VOH6 or http://www.autometer.com/unive...ic-speed-sensor.html. Their manual shows it mounted on a U-Joint http://www.autometer.com/media/manual/2650-1634.pdf At $89 I think the pricing is outrageous!

Bicycles use a reed switch for the speedo signal. You can usually hear a "tick" as the magnet passes the sensor. Reed switches are small and really cheap and have a fast response time (it depends, but 400 Hz or higher are possible. Here's one on Amazon rated at 400 HZ. https://www.amazon.com/farhop-...kaging/dp/B01IEE4PEA They can be a bit fragile so should be epoxied into a tube or something. Reed switches have a limited life, but It can be quite long: "Lifetime depends on load conditions. If switching signal loads only, many millions, and indeed even billions of switching cycles can be achieved" http://www.pic-gmbh.com/files/reedinfo_test_en.pdf contains that and more info.

Or, you could roll your own Hall effect sensor. I don't think it would be too difficult. The robot hobby people use them a lot. http://www.robotshop.com/en/hall-effect-sensor.html


quote:
Originally posted by GT4Peter:
The plan is to glue some magnets on the zf ouput shafts and take this signal for the zf.
Like on a bike .
quote:
Originally posted by GT4Peter:
Is there a metric one?


Yes, http://www.autometer.com/5-spe...dash-ultra-lite.html Also, since the speedo is programable, if you calibrate it over a km, then it will read out in km/hr. If you do that, you would need a 200 mph max dial and with that would max out at 200 kph = 124 mph. Probably not what you want Confused

VDO also makes electronic speedos but it appears that 4" is their max diameter.

Another possibility is that you can use your existing speedo face (and can?) and install the Autometer guts in it. There are places in the US that can do things like that. That would probably be less expensive than replacing all your gauges.

Finally, there are electric to mechanical speedo converters that may be your best solution. Here's one example: http://www.speedhut.com/ecomme...rive-Speed-Converter
It has GM/Ford/Chrysler choices which is for the connector for the speedo end which probably won't work with your VDO. Any good speedo shop should be able to modify their cable to your speedo or your existing cable to their box. This unit has GPS built in but also accepts other inputs. Strangely, If you want to use a VSS, you must hook up the GPS to calibrate it. This seems to imply that the output will be in mph: there is no mention in the instructions of kph. So probably this won't work for you.
Try googling: mechanical speedometer to electronic speedometer conversion. There seem to be some other options.
Peter, to DIY-convert a #4490 Autometer speedo to a DeTomaso metric face requires a real leap of faith. First, you must disassemble your current speedo so as to access the face- not too difficult except for removing the delicate pressed-on needle. Then you must take a deep breath and saw open your $265 (USD) Autometer's sealed plastic case so as to swap faces. Unless you are in a different economic class than I, this will take the longest to do. If a cursory fit-check indicates the faces will not suitably interchange, you could have a new face made by photolithography, relatively cheaply. The Pantera 90 (37 made) used an electronic version that has a 300km face and looks & fits like your stocker. I've never seen one except in photos. Roland Jaeckel has/had one with its drive sensor, but it was priced out of my reach.

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