Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Speedometer not working on 2008 Plus 4

Yesterday I noticed that my speedometer is dead. The LED odometer lights up, but the milage stays at 74000 km, and it does not increase. The needle stays at 0 km/h. With the extreme speeding fines in Norway, I need to get it fixed soon.

Has anyone had similar problems?

Greetings,
Harald

Short term get a GPS speedo positioned so you can see whilst driving - maybe worth having anyway.

Apparently this company have been helpful to TM members in the past providing and fitting new speedo LCD display if that proves to be the issue. Maybe you have similar specialist in Norway. In the meantime suggest reseating Speedo display connector behind dash and the wheel sensor itself.

Hi Harald
The obvious question is, has the instrument failed or is there a problem with the speed sensor or its wiring. You could of course simply take the speedo out and send it off for testing. According to DaveW's book however (see page 125 if you have a copy) the speed sensors are quite delicate.

When I had my speedo out of the car to take to the company that RichardV6 points too in his link, I decided to knock up a very simple oscillator to determine the relationship between the speedo reading and the speed sensor pulse frequency. This is a rather crude but simple circuit that enables you to run a rudimentary go no go speedo test on the bench. The oscillator is controlled with a potentiometer that gives you the ability to vary its frequency from about 14Hz to 166Hz and so in my case this varies the speedo reading between about 6mph and 80mph. If you or someone you know has reasonable soldering skills it would not take long to build on a piece of 0.1 inch hole spaced Vero or strip board. All the components needed are available on ebay Connections to the speedo can be achieved with 2.8mm standard female spade connectors. I have included the circuit diagram see below. If you chose to have a go it is of course at your own risk but as you can see from the photo, also below, it worked fine for me. It is imperative that you make absolutely sure that 12volt connections to the speedo are connected the correct way round or damage may result to the speedo. You would need a 12volt supply, perhaps a drill battery or similar. One other point whilst running the test the speedo is clocking up miles or kilometres on the odometer that your car has not done so you would not want to run the test for any longer than needed for a quick check.

Here is a link to a document that provides pin number details for the speedo connections.

https://www.jbugs.com/store/images/...Jqt18Ri3cKR17e4rlaA8GT8l9VtiHVsqWl4_qzN8






Regards Tony

I had exactly your symptoms. Very possibly the speed sensor located on the off side front wheel hub. It is a hollow bolt containing the electronic sensor. Easily broken when wiping away excess grease etc.
“Revotech” make the replacement for about £50+ or so; also available via suppliers like Demon Tweeks.
All about it in past posts on TM & in Dave’s book, as already mentioned.

Mine is on the front of the drive shaft. (my speedo cuts to zero at around 95mph caused by the sensor)
As for road use it doesn't matter, only shows up on track I have not bothered to change the sensor.
(2011 4/4)

Mine still works (+4/2006) but drops out from time to time. The interruption is only a fraction of a second but causes the indicator to swing until it stabilises.
I have not found it's root cause but I don't think it's temperature dependent or a bad connection.

Thank you all for comments and suggestions.

The local Morgan expert, Trond Bråthen, said that he has the necessary parts, and he will help me to get it fixed before MOT.

On my previous cars mechanical speedometers used to last hundreds of thousands kilometers on low price models. Hence, I'm somewhat disappointed that hhis happened so early. Perhaps the electronic stuff is programmed to fail early?

Greetings,
Harald

I just think that electronics are not robust when the environment fluctuates between hot and then cold & damp. Condensation will affect circuit boards over time, and we know that Morgan instruments suffer condensation.

That need not be an issue - the PCB just needs proper protection from moisture. There are several techniques - from a "varnish" to full potting depending on application.

As an aside - I once visited the steel works at Scunthorpe on behalf of my telecoms equipment manufacturing employer. The chaps there told us that ordinary commercial PC's installed on the shop floor failed very quickly because of the atmosphere.