Speedo now reading in reverse

I've read through a few speedo issues and solutions other members have had on here but this one seems a little different.

After heavy corrugations at our Easter break I noticed the speedo was jolting around within 10km's of actual speed whilst we were away.

On the way home on the freeway doing 110km's the speedo fell to the other side of the gauge (Reading 200km's) and stayed there.

Now it sits on that side at idle but when you drive the car it starts to read backwards and will read 140km's at 60km travel, etc.

It's almost like It's reading in reverse now???

Does anyone have any suggestions or things I can look at to isolate the problem or should I just get a whole new cluster or?

Yes very strange indeed. Rodney might shed some light hopefully.

Just drive around backwards... problem solved.

Probably cause a few bowel movements on the Motorway but thats life

If the Odometer is going backwards as well I'd leave it as it is for 100,000 or so

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Originally Posted by the evil twin

Just drive around backwards... problem solved.

Probably cause a few bowel movements on the Motorway but thats life

If the Odometer is going backwards as well I'd leave it as it is for 100,000 or so

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I didn't actually check that...lol

Mudnut has been setting himself up to test and repair GQ instrument clusters, wonder if he would have any idea.
Does everything else work ok?

Bear with me as I am still setting things up. I have just pulled the tb42e unit apart to sus out what may be going on with yours, Andy. It is just a moving coil meter, with two field windings instead of one.(one powered from ignition and one powered by the speedo sender which is cleaned up by the speedo electronics) I think that the two windings provide for stability and give a more accurate reading. At this stage I can only guess that there is a fault in the speedo electronics as the speed sensor sends an AC signal. There may be a blown diode which is letting the AC signal through. The heavy vibrations may have interfered with the pointer spring too. I would need to have a look at your speedo, too test it properly.

Yours is a TB42 E isn't it Andy? With ignition off. If you take off the dash surround and undo the four cluster screws then lift out the cluster and tilt it to see the back. You should be able to see the speedo signal and power inputs, which are four silver phillip drive cheese head screws. Looking from the above, top one is marked 2P, the bottom is IGN. The side ones have a bit of Japenese followed by - and +. These are the speedo signal inputs. To get a good measurement, I made two 50cm long test leads, by stripping a half centimetre of the insulation from each end. Loosen the -ve and +ve. Slip one lead under the -ve and tighten the screw, making sure that no strands of copper are loose and able to contact any other part of the circuit. Do the same for the+ ve. Re position the cluster and do up the four anchor screws. I taped the other ends of the test leads to the probes of a digital multimeter and set the dial to AC volts. Get an assistant to drive. See that you get a small voltage which should rise to approx 5 volts as the speed increases to 60kph. When you have finished, remove the leads and re tighten the screws, firmly, but do not over torque them. Sorry, pictures won't load at the moment.

Edit, changed the signal output to approximately 5 volts

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Originally Posted by mudnut

Yours is a TB42 E isn't it Andy? With ignition off. If you take off the dash surround and undo the four cluster screws then lift out the cluster and tilt it to see the back. You should be able to see the speedo signal and power inputs, which are four silver phillip drive cheese head screws. Looking from the above, top one is marked 2P, the bottom is IGN. The side ones have a bit of Japenese followed by - and +. These are the speedo signal inputs. To get a good measurement, I made two 50cm long test leads, by stripping a half centimetre of the insulation from each end. Loosen the -ve and +ve. Slip one lead under the -ve and tighten the screw, making sure that no strands of copper are loose and able to contact any other part of the circuit. Do the same for the+ ve. Re position the cluster and do up the four anchor screws. I taped the other ends of the test leads to the probes of a digital multimeter and set the dial to AC volts. Get an assistant to drive. See that you get a small voltage which should rise to approx 2 volts as the speed increases. When you have finished, remove the leads and re tighten the screws, firmly, but do not over torque them. Sorry, pictures won't load at the moment.

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ABs is a TD42 Craig.

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Originally Posted by mudnut

Yours is a TB42 E isn't it Andy? With ignition off. If you take off the dash surround and undo the four cluster screws then lift out the cluster and tilt it to see the back. You should be able to see the speedo signal and power inputs, which are four silver phillip drive cheese head screws. Looking from the above, top one is marked 2P, the bottom is IGN. The side ones have a bit of Japenese followed by - and +. These are the speedo signal inputs. To get a good measurement, I made two 50cm long test leads, by stripping a half centimetre of the insulation from each end. Loosen the -ve and +ve. Slip one lead under the -ve and tighten the screw, making sure that no strands of copper are loose and able to contact any other part of the circuit. Do the same for the+ ve. Re position the cluster and do up the four anchor screws. I taped the other ends of the test leads to the probes of a digital multimeter and set the dial to AC volts. Get an assistant to drive. See that you get a small voltage which should rise to approx 2 volts as the speed increases. When you have finished, remove the leads and re tighten the screws, firmly, but do not over torque them. Sorry, pictures won't load at the moment.

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Happy to wang you some coin to fix this mate if I can't work it out myself which is very likely...lol

No coin necessary, Andy. Anyway, I can't help, as I only have the one cluster, I am using to set up. The test procedure I laid out, should still work for your speedo. It confirms your sender and wiring harness are all good. If the signal is ok, then another unit from a wrecker or one of your minions from here may be the go. It is fairly easy to swap out the speedo so you can retain your odometer. Pop the black cluster shroud and clear cover off. Unplug the odometer connector. Undo the screws, ( also one near the high beam and indicators) and gently lift out the gauge. I could sling you a few bucks for postage, and your second cluster and stuffed speedo, so I can have go at dissecting it. It will also give me some spare gauges.

So if he is just striping the speedo out will one out of a TB work for that?

That, I don't know, yet. The TB42E has an extra terminal 2P which goes to the ECM. I did ask whether it was an input to the speedo or an output from the speedo to the ECM, for engine and auto control, but I can't find the post for the question or answer. So I have just run a test with the oscilloscope and the 2P creates a very weird pulse of about
35 millivolts and looks like a heartbeat on a hospital monitor. Can someone post up a picture of the back of a TD42 gauge cluster, please.

Well finally something has gone right.

Fixed the speedo using highly advanced tooling.

I just took it down the street and did the usual banging dash as I have done a hundred times but to no avail.

I finally cracked it and smashed the top of the dash pretty hard and it bounced back to the other side and is currently reading exact speed...lol

Not sure how long that will last for but one problem temporary solved for now!

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Originally Posted by AB

Well finally something has gone right.

Fixed the speedo using highly advanced tooling.

I just took it down the street and did the usual banging dash as I have done a hundred times but to no avail.

I finally cracked it and smashed the top of the dash pretty hard and it bounced back to the other side and is currently reading exact speed...lol

Not sure how long that will last for but one problem temporary solved for now!

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You're ready for the simmo! Haha

Quote:

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Originally Posted by AB

Well finally something has gone right.

Fixed the speedo using highly advanced tooling.

I just took it down the street and did the usual banging dash as I have done a hundred times but to no avail.

I finally cracked it and smashed the top of the dash pretty hard and it bounced back to the other side and is currently reading exact speed...lol

Not sure how long that will last for but one problem temporary solved for now!

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Now that's my style of fixing things

Haa Haaa. All my technical B.S.and I shoulda just recomended a knockometer. I suspect it might fail again if the speed and road conditions are right.

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Originally Posted by mudnut

Haa Haaa. All my technical B.S.and I shoulda just recomended a knockometer. I suspect it might fail again if the speed and road conditions are right.

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You lost me when you said take the dash off...lol

Hey do you wanna come around to mine with a sledge hammer and knock my car a couple of times and turn it into a 4.2td.

Sent from me using Forum Runner

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Originally Posted by ab

well finally something has gone right.

Fixed the speedo using highly advanced tooling.

I just took it down the street and did the usual banging dash as i have done a hundred times but to no avail.

I finally cracked it and smashed the top of the dash pretty hard and it bounced back to the other side and is currently reading exact speed...lol

not sure how long that will last for but one problem temporary solved for now!

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you have knocked all the dust out of it now
over the last 12months well since coopers creek
its built up and dew and moisture has sent it haywire
now you should get another twenty years out of it

Quote:

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Originally Posted by AB

Well finally something has gone right.

Fixed the speedo using highly advanced tooling.

I just took it down the street and did the usual banging dash as I have done a hundred times but to no avail.

I finally cracked it and smashed the top of the dash pretty hard and it bounced back to the other side and is currently reading exact speed...lol

Not sure how long that will last for but one problem temporary solved for now!

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Being a qualified electronic technician I can verify that is a tried and proven repair practice.

Quote:

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Originally Posted by AB

Well finally something has gone right. Fixed the speedo using highly advanced tooling. I just took it down the street and did the usual banging dash as I have done a hundred times but to no avail. I finally cracked it and smashed the top of the dash pretty hard and it bounced back to the other side and is currently reading exact speed...lol Not sure how long that will last for but one problem temporary solved for now!

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On ya FONZ....... Eeeeyyyyyyyyyyy

Your a rough man AB, after all your GQ does for you and this is how you treat it..........LOL

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Originally Posted by Yendor

Your a rough man AB, after all your GQ does for you and this is how you treat it..........LOL

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I know I know...lol

You should see it now Rodney, if the previous owner saw it now I would get a backhand. When we shook hands he said to me I'm happy it's going to a good bloke who will look after it.

I'm still following the tradition of putting the Anzac badges on the visor but aesthetically it's looking rough. Don't get me wrong mechanically it's absolutely sensational.

When my speedo played up - I actually pulled the dash apart and wnet for a drive while tapping the board - its how I found the intermittent problem.

I would give the board an eyeball and check for cracked solder joints.

I found I had a the legs on the crystal where corroed and intermittent.

I replaced the xtal with a 4.097 it 4.19 on the board

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Originally Posted by GQ TANK

When my speedo played up - I actually pulled the dash apart and wnet for a drive while tapping the board - its how I found the intermittent problem.

I would give the board an eyeball and check for cracked solder joints.

I found I had a the legs on the crystal where corroed and intermittent.

I replaced the xtal with a 4.097 it 4.19 on the board

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Where did you source the crystal, Tank?

AB check this thread out from Dale mate http://www.nissanpatrol.com.au/forum...26188-Gq-stuff

I got the xtral from work - it was on a old circuit board.

I only found a online mob in ebgland that had the 4.19 mhz on the sehlf. But as the 4.097 rock worked you might be able to get one that is close from RS components

I will check them out, thanks.

I have built a simple speedo signal generator, and have been able to replicate the problem on the test bench.

When the speedo is sitting at 100- 110kmh and the supply voltage is interrupted, the needle drops to the wrong side and begins to play up. This test points to there being an intermittent bad connection in the supply circuit.

I popped the plastic cover open and used a small piece of hooked wire to lift the needle back and it works perfectly now.

If the problem recurs, at least you have a starting point to begin trouble shooting.