Whys my new speedo out? 130mph to 140mph conversion?

[Bailes1992]

My old instrument cluster went upto 130mph and didnt have a rev counter. I've just replaced it eith a 140mph version and it all works except the speedo aint right. I can hit 41mph in second on my normal 130mph speedo but it's barlkey touching 25mph on my new one?
Can anyone shed some light on this?

[Bailes1992]

Think theres something wrong with the cluster now.
I reset the mileage on it yesterday and when I went around the block to test the speedo the milage come to 0.7 miles when I got back to the house.
I just checked on my old speedo and it come to 0.7 miles when I went around the block aswell so it's definatley getting the right feed

[eoin27]

I have a feeling that the speed sensor is set up to read on the older clocks. So its underestimating on the new ones.

One thing that makes me suspicious is that if the new one is 140mph, then the 40mph mark is lower down the clock so it should be over estimating if anything.

[Bailes1992]

Thing is the new speedo I got has a stamp for '96 on it and my car's a 98 model.
When I fitted the new cluster with the rev counter I reset the mileage and took it round the block and come back with 0.7 miles.
I put my old cluster back in and went around the block and it is infact 0.7 miles which tells me it's defo getting the right feed?

[eoin27]

I understand that. But the car thinks the needle is in one place indicating a particular speed when it should be in another. The needle isnt calibrated properly.

Take this from someone who hasnt a clue about speedos. Never had to go near that unfortunate business. Just a thought......Can you manually push the needle upwards to the desired speed? Say your doing 40mph (via a sat nav info) and it says 25mph, can you push it up to 40? I think it will stay. And return to zero when switched off. I had a set of BMW clocks open before and you could do this.

Please be careful if you do decide to try this. Perhaps have someone else drive the car. Again, this is all speculation on my part. The disclaimer is in the post

[highlander]

Disclaimer: I have no idea about anything related to cars, or electronics, really.

That said, here is my take on the situation:

The speed sensor generates an analog signal. The faster the car is, the stronger that signal.

The electronic circuit of the original speedo clock was designed to receive the signal from that particular model of sensor. By which I mean that while the signal from the speed sensor is the same, the processing of that signal before it reaches the gauge needle itself will be different.

It will be directly proportional to your speed, right enough, so the faster you go, the higher the speedo will go - but it will never match the numbering on the gauge clock, simply because the analog signal that is being received is being manipulated incorrectly.

I think you won't be able to use that particular speedo in your car.

This may be different if your car was a D9, but I don't know for sure. See my disclaimer.

I don't know if it would be possible to use just the original speedo and attach it to your new set of clocks or not. Maybe one of the D8 owners or more technical members could confirm or refute that.

Cheers
Graeme

[eoin27]

I don't know if it would be possible to use just the original speedo and attach it to your new set of clocks or not. Maybe one of the D8 owners or more technical members could confirm or refute that

Theres a thought!!

[Bailes1992]

What I'm confused about is why the mileage reading is correct if the speedo isnt?

Just looked into replacing the speedo on my old one.
Heres my new cluster...

This is what it looks like from behind.

This is it with the back taken off...

Now if I replaced this motor from my old cluster would i get a better reading?



Then I could cut the speedometor and temp gauge out from my old one and fit it to this one and get a right reading?

[Welly]

Disclaimer: I have no idea about anything related to cars, or electronics, really.

Just got me a new Sig

[Doggy]

Me too!

[highlander]

Oh, you guys!

[Welly]

Highlander, I'm not taking the mick out of you with the Sig it's just that your statement touched my weird sense of humour. I hope you don't mind.

Better get back to the OP's topic.......

[swiss]

Swapping out the motor might work, presumably the needle is returned to zero by a spring and so for a given speed a given level of power is supplied to the motor in order to overcome the known resistance of said spring in order to display the correct(ish) speed. *pause for breath*.

Now, rather than individual instruments like you get on classic cars, the 406 has a PCB with various configurations of instruments printed on plasticard. My question therefore is, is the PCB universal or is it specific to those panels with a clock vs rev counter, oil gauge or no oil gauge, etc etc. My reasoning being, how would it know whether its output was a clock or a rev counter, all it cares about is outputting what it believes to be the right signal. Therefore you'd definitely need the PCB from the new dash and therefore it would follow that you strip the corresponding hardware ie. the speedo motor as you describe because the PCB doesn't know what it's attached too, only what it's supposed to do.

Now, if that still doesn't work it would suggest that the PCB is interpreting the input signal correctly but the speed transducer is not giving the correct output for the PCB to crunch. Therefore you'd want the complete set-up from the car you pinched the new dash from, inlclidling the speed sender. Of course it might pay to try swapping out the speed sender first, before butchering the panel


Disclaimer: I went to the Highlander school of automotive whatsit, so I don't what I'm talking about neiva

[highlander]

Welly, I know Guess that serves me right for that quip about you not being a proper club member over in your Astra thread

Incidentally, you see the black bit of card that shows all the clock faces on it... I was wondering if it is possible to get one of those for my D9 that is white instead of black. So I'd swap the bit of card over and it would give me white clocks, without me having to change out any of the electrical bits of the clocks?

And back on to Bailes1992's original issue - sorry, I have no idea why the mileage clock would be correct while the speedo is out. Unless the mileage is taken from a different sensor to the speedo, though I can't see a logical reason why that might be the case.

[omega]

well the new dash came out of a 406 1.9 diesel with 15 inch wheels on a p plate