Speedo keeps flipping back down to zero! Any ideas?

[hairyaardvark]

Hiya

was hoping someone had seen this before and can help suggest a cause and fix.

'55 Sag, although i think the speedo units are the same across Sag, T350 and Tam?

Anyhow, just recently the speedo needle has started intermittently flipping down to zero whilst I'm cruising along. The digital readout goes to zero at this point as well. This situation can last anywhere between one second and 10 minutes or so, then suddenly, without me changing gear, slowing down/speeding up, or going over a bump or something, it'll all flip back to life again and all will be normal !

Most odd - and the rev needle seems unaffected by this jollity, continuing to act normally throughout.

Does anyone have any ideas? I guess some sort of sender is failing, but where/how can I check?

cheers ears
DaveR

[Fume troll]

Maybe a dirty sensor? If it's the same as the Tuscan it's by teh diff, and can get dirty and start giving odd results.



Cheers,

FT.

[hairyaardvark]

Great - thanks fumetroll! will check that out

[julianc]

Most likely the speed sensor - I had this problem a few years ago and a new speed sensor was the solution in my case.

Julian

[Jezz172]

Mine started doing that last week.

Turned out to be the battery discharging due to a dead alternator, the rev counter was the first thing affected

[hairyaardvark]

Hhhmm I hope it isn't that! Battery seems fine, showing 13.4 V, car starts and runs OK ....?

[shorts!]

Though I've also had Jezz172's problem it is much more likely to be a sensor issue, dirty, too wide a space or just knackered sensor.
In my experience if it is in relation to the alternator (or the infamous 100amp fuse) the dials will flicker a couple of times before coming to rest at zero and the radio, if you have it on, will go off. This is a suitable time to get out of the outside lane of the motorway and open a window as pretty soon you will have no electrics at all and you'll be cruising to a standstill with no power, no servo and no power steering.
But it's almost certainly your sensor.

Edited by shorts! on Thursday 18th June 11:59

[hairyaardvark]

Haha let's hope it isn't the alternator then - yikes !!
Will update this thread when I find out for sure ... in case anyone else Searches for the same problem (if Search ever returns).

cheers all
DaveR

[Fume troll]

BTW the image above is from the mytuscan.co.uk site, it's often useful for other SP6 cars.

Cheers,

FT.

[nwarnes]

Same problem on a Tamora. Was speed sensor wiring / connection apparently. Connection by fuel pump hard wired and problem resolved.