Hi all

As I was driving home today, I noticed my speedo quit... I'm suspecting the cable... How do I go about getting to the speedo unit? I've consulted the Haynes manual, very limited... What items need to be removed to gain access, and how do I go about removing them?

Many thanks.

 

To remove the speedo and tach you push them in firmly and turn about 1/4 turn. This will disengage them from the dash. Hopefully someone will remember which direction to turn...because I can't. Or, of course, you could just try both directions

Hopefully there's enough slack in the cable to allow you to pull the speedo out and easily disconnect the cable from the back of the speedo

Are you sure you don't have the electric speedo? I think 1982 was the changeover year

Cheers
DD

 

Anti clockwise in my S1, I would assume it is the same. But first time I didn't push in hard enough and removed the glass from the speedo, that was fun to get back on with the speedo still stuck in the dash.

 

Nathan:


Get down and under. I think your V12 uses a GM TH 400 auto box.
The speedo drive should be toward the right rear.


There, you should see a box and wires for an electric speedo or the housing for the mechanical old tech style.


Sudden failing suggest and electric unit. Very likely a wire or connector issue.


Caveat: a lot of conjecture here.


Carl

 

Many thanks all, being a 1982 car that's had a new speedo put in by the PO this will be interesting... Symptoms have me in 2 minds... Firstly, the needle shot up to 140, returned to 120 and pegged, didn't flicker after that... Secondly, the milage and trip meter both stopped turning too, thirdly, the needle always used to jump a tiny bit everytime the ignition was turned on, which it still does... So I'll check under the tranny soon and post what I find.

 

When i took my speedo out i used a partially used roll of masking tape, it fit inside the glass area of speedo, gives you something to hold and is sticky enough to grip it.

 

That suggests the electric speedo

Transducer failures are fairly common. It's located on the LH side of the trans, sorta towards the rear. Wires burnt on the exhaust pipe are a possibility as well

Cheers
DD

 

Thanks for the replies, so is this whole unit electrically driven? Even the milage and trip meter? The failure of all 3 has me baffled...

 

Speedometer, odometer, and trip computer (when fitted) all driven from the same transducer. Cruise control as well, for that matter !

Cheers
DD

 

Aha, perfect, now I'm sure I'm staring at the problem... A nut, little shaft, and then a big round thingy (bigger than the nut) with wires (looks like 2) coming out? Can I remove it without draining my tranny oil at the same time?

 

That's it

No need to drain tranny

You get a dribble out of the hole, perhaps. That's all


cheers
DD

 

Perfect, thanks a mil Doug!

 

Just a quick one, any idea how to go about testing this thing?

 

Nathan:


Never tried or even seen one. As I understand, "sorta", it is a pulse generator.


That suggests an on bench method to spin it. A corded or cordless drill motor??? Possibly, doable! Then an oscilloscope? Maybe???


Lower level testing'


1. It is intact.
2. It is clean.
3. I turns freely.
4. The connections are clean and intact.
5. As Doug relates, the sires are intact.


Or, a known good transducer.


Carl

 

Thanks Carl, as I understand it produces AC current, I've used an oscilloscope before, but sadly don't own one, I've got a multimeter though... Now, there are 2 wires here, yellow (+) and brown, if I connect these to the multimeter and spin it should I get a reading on the AC function?

 

Nathan:


As said before, I don't know. But, your idea sounds reasonable.
Can't hurt to try it!


Alternate: Google, "How to test a GM speedometer transducer?".
Or, an archive search on this forum.


Carl

 

Well I tried, and as predicted it didn't hurt. Got a reading on the AC function, but it didn't quite add up, after a while I figured my multimeter was picking up AC from the electric drill, touched the tip of the spinning drill lightly on the shaft and up went the reading, wish I could explain that one... Spun it with a mechanical drill and got no reading at all.

 

Any chance anyone knows if this is a Jaguar-specific part or if it is a GM / common part? Starting to count the pennies for the Jaguar one...

 

Just a guess. GM pulses probably differ from Jaguar pulses.
Might fit a GM unit OK, but the speedo would be way off.


Mine is!!! GM 4l60E transmission and Jag speedo.


Open it? clean it? Study the circuitry? I don't think it generates current. So one wire should be a source and the other goes to the speedo?


Not sure what the AC from the drill did??? The RF around it's electric
motor? Reading on the VOM???


Carl


Carl

 

Try the research I suggested.


Carl