Speedo AND Tripmeter not working ?????

[Ian Comerford]

Recently both the speedo and tripmeter stopped working on my '79 SC. I changed the sender about a year ago so it SHOULDN'T be that (?). I have looked at lots of PP threads on speedo faults but have failed to find one where both parts of the gauge no longer function. Is it possible that plastic cogs in the speedo have failed that affect both functions or is it more likely to be the sender again? I do not want to strip the speedo if it is not likely to be faulty.
Grateful for your advice/experience

Ian

[Ian Comerford]

Anyone help with this one please?
Could the pot metal wheel have come loose on the shaft AND a plastic cog stripped its thread? Do these two parts relate to the two faults I have mentioned?

Thanks in anticipation

[bigchillcar]

hi ian,
doubt this helps, but my '74 speedo has always worked while my odometer has never..my understanding is that there is a plastic gear that easily strips when people 'reset' the trip while the car is in actual motion. guessing by sender you mean that your speedo is electric instead of mechanical like mine?
ryan

[350HP930]

If you change your sender, check the connector in the tunnel. Perhaps it just came loose.

The one time my speedo went out thats all it was.

[Gunter]

The old rumor just will not die. It does not matter if you reset while in motion or standing still. If the mileage counter, and the trip meter, and the speed indicator has stopped, I would suspect electrical. Pull the speedo out a little and check if it gets 12V. Do a search on this board for more info for speedo.

[Early_S_Man]

TD terminal of the CDI unit is for Tachometer Drive, not speedo!!!

The speedo needs the following to function: power, ground, and the two leads from the magnetic reed switch inside the speedo sender ...

[Gunter]

You are right Warren. Not enough coffee this morning.

[Ian Comerford]

Thanks guys,
This gives me a little more to focus. Can anyone with knowledge of the internal workings of the speedo just confirm that it is very unlikely to be stripped cogs/loose shaft that is causing the lack of speedo/trip/odo?
Thanks again

Ian

PS The speedo may not be a legal requirement for the MoT test, but it sure does stop speed cameras ruining your day!!!!!!!!!

[clevy70911T]

Take it apart and see. Just take your time prying the outer black ring off.
My limited eyeball experiences with the speedo makes be believe it's electrical too. I postd a few pics below showing the odo unit and my missing rubber gear. I can find it and take inside pics of the speedo if you think it will help you.

Link to the reset-button causing the odo lock up thread.
Speedo repair

[Ian Comerford]

Thanks Scott,
I'll have a look at the electrics before I break into the speedo, I will report back with what I find.

Thanks again guys

Ian

[Ian Comerford]

Finally got around to checking the output from the sensor at the weekend, a long time without a speedo I know!! No speeding tickets yet though. There was no reading at all, ordered a new one. It took half an hour to fit because I had replaced the same thing last year. Bingo, I now have a working speedo. If all the speedo functions cease working then it is most likely to be the sender, not plastic cogs.

Ian