Speedometer Terminals Identification

[Guest]

Has anyone out there got a diagram of the back of the Speedometer showing the terminals and their use?

The back of my Speedo has four terminals, however only three of them are connected and at present the Speedo is not reading correctly. I think that a terminal has become disconnected from terminal "A", but I cannot see any loose connectors.

I have tested the voltage at idle and all terminals have voltage as follows
- Earth
- Positive (12v)
- 7.5v
- 3v (aprox)

Are all four terminals supposed to be connected? If so what does the terminal "A" do?

Thanks

 

[bones]

Here's mine I don't know what the other voltages are that aren't marked. The pulse current is extremely low so might not register on anything but a 'scope.

 

[Guest]

Thank's Bones. So I presume the one from the sender is for calculating speed. What about the cruise? What is this one for?

 

[bones]

Yes the one marked sender is for the pulses from the gearbox for the speed calculation. The one marked 'cruise' is for the optional cruise control. I did want to make a joke there but couldn't think of a politically correct way of saying it. []

 

[Guest]

Yes there are so many things you could have said there. OK so it is for cruise control - neaver knew that that was an option in the 1982. You're not supposed to cruise in a Porsche. I guess that means there could be an issue in the speedo itself. Basically I have speed but do not have the mileage counter.

Do you know if there is a way to repair the speedo so that the mileage counter works again? I realy would like to avoid having to buy a new speedo.

Thanks

 

[bones]

It may have been discontinued by then but I imagine the clocks are the same. You may be in luck for a cheapish repair if the electronic side of things are working ok then the good news is the oddometer is driven by sone mechanical gears in the speedo which can break. The repair is detailed in Wayne Dempsey's book, '101 Projects for Your 911'. Have a look at this to see if you can handle what's involved.
http://www.p-car.com/diy/odometer/
You can them repaired abroad in the U.S. or here at Speedy Cables but I don't recommend them as they are slow , provide zero customer care and are extremely expensive, trouble is I can't find anywhere else. You could get a secondhand instrument from a breakers and adjust the mileage if you want. About £80.00 last time I bought one, a repair would cost way more from Speedy Cables, love the name! []

 

[Guest]

Well this could explain the rattling noise I noticed. Hmmm time for a new gear. Looks easy enough. Now just to find the gear. Do you know where in the UK I can get one? Otherwise I'll gust get it sent from the US.

Cheers

[]

 

[bones]

Sorry I don't know where you would get them in the UK try VDO/Seimens in Birmingham or somewhere like
www.type911.co.uk
might be able to help

 

[Guest]

Will sort one out from Odometer Gears. Does anyone know which size would be the right one?
20x21 tooth
20x22 tooth
20x23 tooth
20x30 tooth
20x32 tooth

Thanks

 

[Guest]

I have just taken my speedo apart and are waiting for the Gear, mine is 20x30, my car is a US spec which is what the guy said and the euro spec should be 20x32