Speed sensor

Need some help with a speed sensor for G50/50. I am told by the people at Classic instruments that I need a 8 pulse sensor and have not been able to find out what the Porsche sensor is. Anybody have any experience with how to make my speedo work. /ubbthreads/images/graemlins/confused.gif


Tim Kay

Lifetime Supporter
Sorry I can't be of help here Simon. I too am interested how to attach the speedo to the G50.

I do have a question to you. What brand of speedo are you using (I aasume it's electronic vs mechanical)? My current speedo is mechanical driven off my Renault trans. My understanding is my G50 can only work with electronic. So I need to find an electronic speedo as well.

Maybe David Briggs can chime in here. I believe he is running an exterior electronic sensor off his inboard CV joint in his CAV\ZF.
I have a slightly different twist on the same problem. Patrick Motor Sports installed a strenghtened side plate on my G50/52 that does not have a hole for the speed sensor.

I too have a Classic Instruments speedo ... and need a sensor to plug it into. Guidance would be appreciated.


The Porsche speed sensor is basically a magnet that "reads" gear teeth. If you could locate the sensor on the outside of the new plate(in the same position as on the stock plate), it MIGHT work, since aluminum is a non-ferrous metal, and shouldn't bother the "signal".
I have the sensor part # somewhere, if anybody needs it.

Make that four of us interested in which sensor to buy for the G50. The stock Porsche sender costs ~$300!

Tim Kay

Lifetime Supporter

Along with the sensor part # what info do you have for the speedo gauge that will work with that sensor and match the GT40 guages?

Being the DRB's are commonly g50's there must be a package setup for this application /ubbthreads/images/graemlins/cool.gif
You can use a VDO gauge, the sensor is mounted externally and counts the bolts that hold the CV to the transaxle, Seems to work well enough.

Peter Delaney

GT40s Supporter
My G50 came with the standard speed sensor still installed. I used VDO "Cockpit Vision" instruments, & the speedo is magic - you just set it up in cal mode, drive 1 measured km, then hit the set button - everything is automatically calibrated & it just doesn't care how many pulses per rev it gets ! It turned out to be accurate within 2kmph at 100kmph when measured against Trevor's calibrated system.

The VDO can handle "Hall Effect", "Interruption Oscillator", or "Induction" sensors - just plug the sensor into the right set of terminals on the back of the speedo. I can't be 100% sure (too long ago), but I think that the G50 sensor was an induction type as per Bill B's comments.

I have no idea of the number of pusles/rev, but Autohaus (Posche g/box experts in the US) would certainly know - they are very helpful guys, even if they don't get to sell you their staggeringly expensive gear sets !

Kind Regards,

Peter D.

I'll start digging for the sensor part number.

I should have it for you later today.

I also have the VDO "Cockpit Vision" gauges.

Once I had my speedo set, I checked it against a handheld GPS.

It was accurate to within a few tenths of a MPH.

I think Peter is referring to Powerhaus II (Roger Brown).


Peter Delaney

GT40s Supporter
Bill B, being a lot younger than me, has total recall when it comes to the names of good contacts !!

Kind Regards,

Peter ....... Al Z .... someone or another !!
Just to be slightly different, I want to use a mechanical Smiths Speedo (the electronic has a digital trip meter). I found the following people
I got an email saying the speedchanger mechanical is now available back in February, but it is still not pictured on the website.


Gulf GT40
Lifetime Supporter
FWIW - I have chatted with the fellow who did the Speedchanger, I was also waiting for a TachChanger for a mechanical tach that I wanted to run in my 65 mustang. I think he finally did finish the TachChanger mechanical earlier this year, which was missing the part that drives the mech tach, but it ended up being costing a bit much and I just picked up a mech tach drive dist (dizzy) off of Ebay for a much lower cost. His pricing was something like $130 USD for the electronics, and I want to say about $180USD for the Motor drive portion. ($$ are what I recall quoted)

The motor drive looked like a motor inside of a pvc pipe end cap with some brass fittings with a cable drive coming out. Nothing pretty, but not sure if that was the production.

It is a good solution however if you must run the mechanical stuff.

His site www.terf.com I had the links to the tack/spedo driver but that has long been deleted. The site is really bad and has not to many images and everything is and has been under construction for when I found them in 2003. He was very helpful when chatting so better to email then try to use the site.


Lynn Larsen

Lynn Larsen

The Porsche transaxle puts out the standard European pulses per mile which is higher than US 8 pulses per mile. (I think the European standard was/is 32 ppm, but don't take this as gospel.) The Classic instruments speedo can adapt this via it's dip switches. You can also use an inline adjusters which is what I did. I did this more as signal repeater that would boost the signal for use not only by the speedo, but also by the EEC-IV engine management computer. (There are other advantages like signal shaping and amplitude that can be useful depending on what you want to use the signal for.)

A few other notes of caution: don't run the speedo signal wire in the main loom/harness. Run it by itself. I also used Cat 5 as the twists in the cable helps protect it from spurious signals. I used a 4 pair cable, using one pair for signal, one pair for reference and I gounded ONE end of the remaing two pairs. (DO NOT GROUND BOTH ENDS OF SHIELDING; this can allow a ground loop which can really cause your signal problems!)