Fuel Gauge/Sender mismatch?

[svenedin]

KevinB

You've got a later S5 post '64 Dash, with the shiny panel around the Speedo, but you have a Speedo from a S3 fitted with a 4.55 Diff.
So it really depends what Diff your car has.



Then what's that with the green wires, fitted to the Speedometer case screw?
Which is what I earlier suggested may have been done by the installer.

I have no idea. It doesn't look like a Smiths voltage stabiliser.

Stephen

There were a couple of different part numbers used, initially 33H 2132 then changed to 27H 7821.
Perhaps it's one you haven't seen.
That's without considering one from a comparable period model.
This one looks like it might be it, from a Ford, but likely still Smiths: https://www.ebay.co.uk/itm/257093931482

Prior to it being fitted, the green wires were simply attached to the Fuel gauge input terminal.

Yes it could well be that.

So then if we assume there IS an instrument voltage stabiliser why is the fuel gauge misreading?

Stephen

[KevinB]

Thank you all. Bill, I have dealt with that exposed wire, thanks.

Finding all this confusing! I'm not sure what action to take yet.
The car has had £000s spent on it in recent years and much is documented through invoices etc. There is a pencil note about a new Speedo head, but no detail I have found yet.

I will try to take better photos tomorrow. I did notice a serial number somewhere. Also, I should put in more petrol and see what the gauge does.

[svenedin]

Modifications are indeed confusing which is why I dislike them! Factory standard cars are so much easier. We need to know why an earlier speedo was fitted to a 1967 car. It should have a black speedo like in my picture (from my 1969 car) 1408 turns per mile (see speedo dial). Your speedo is 1504 turns per mile. Does the speedo indicate the correct speed? Compare with satnav or those radar digital speed displays seen on some roads.

Stephen

IMG_2074.jpeg (3.38 MiB) Viewed 1917 times

[myoldjalopy]

We may never know why it was changed but, were it that the original had failed in some way, logic would dictate an identical replacement. The black speedos are not hard to find, so maybe a PO thought a gold speedo was prettier, without thinking of the consequences? Or he/she had a gold-faced one just lying around in the back of the garage? Who knows what goes through people's minds....
Personally, I would get the correct black-faced speedo (plenty on Ebay) and put the car back to standard (assuming nothing else was done to the car which might affect the readings).

[KevinB]

Firstly, thanks Stephen for the photo of your Speedo. I now know what I should aim for. And as for the current speed accuracy, I haven't driven it on the road enough yet to know unfortunately, with all the unreliability, but from the points on diffs and turns, almost certainly it's innaccurate.

Thanks myoldjalopy, I agree I should source the correct black Speedo. And to answer your earlier questions about my 'bracketry' puzzle, the right-hand crosshead screw was inside the slotted bracket, so I couldn't access the screw head!
I realised this when after the wd40, I managed to slide out the Speedo!

[myoldjalopy]

We often have to put things right after purchasing an old car, I'm afraid. But its not serious.
And could this be the other half of your story? - a black-faced speedo with a gold-faced gauge!
https://www.ebay.co.uk/itm/227485662932 ... SwKs5qWjmh

[KevinB]

And could this be the other half of your story? - a black-faced speedo with a gold-faced gauge!
https://www.ebay.co.uk/itm/227485662932 ... SwKs5qWjmh

Haha, I looked at that yesterday!

[geoberni]

Firstly, thanks Stephen for the photo of your Speedo. I now know what I should aim for. And as for the current speed accuracy, I haven't driven it on the road enough yet to know unfortunately, with all the unreliability, but from the points on diffs and turns, almost certainly it's innaccurate.

Thanks myoldjalopy, I agree I should source the correct black Speedo. And to answer your earlier questions about my 'bracketry' puzzle, the right-hand crosshead screw was inside the slotted bracket, so I couldn't access the screw head!
I realised this when after the wd40, I managed to slide out the Speedo!

As I said last night, the Speedo you have fitted now is intended for use with a 4.55 Diff.

From Stephen's image, his is intended for a 4.22 Diff.
Caveat, all this info from the Potteries website, which isn't a complete list, but is generally correct in my experience except for some of the fitment details. For example, there is a Black Face Speedo listed, with the same 1504 TPM, for a 4.55 Diff, but the list says that was for a S5 LCV.
https://potteries.mmoc.org.uk/ID/Speedo.htm

Before you go off changing the Speedo, check to see which Diff you have.

It's not worth cross checking all the options listed in the Service Part List AKD 3541, the version widely available for download doesn't even list Stephen's model, so it's not the final version.

[mike1864]

Seeing as how the whole speedo panel is such a tight fit in the dash aperture, the side screws seem to serve little mechanical purpose.
I don't think I've ever tightened mine!
But maybe they were designed to guarantee an earth. But doesn't the speedo cable outer ensure that?.

[geoberni]

Seeing as how the whole speedo panel is such a tight fit in the dash aperture, the side screws seem to serve little mechanical purpose.
I don't think I've ever tightened mine!
But maybe they were designed to guarantee an earth. But doesn't the speedo cable outer ensure that?.

No, the Speedo Cable doesn't ensure that, and you wouldn't want it to be used for that purpose anyway.
But yes, the fasteners do serve that purpose and they don't need to be particularly tight.

[myoldjalopy]

Firstly, thanks Stephen for the photo of your Speedo. I now know what I should aim for. And as for the current speed accuracy, I haven't driven it on the road enough yet to know unfortunately, with all the unreliability, but from the points on diffs and turns, almost certainly it's innaccurate.

Thanks myoldjalopy, I agree I should source the correct black Speedo. And to answer your earlier questions about my 'bracketry' puzzle, the right-hand crosshead screw was inside the slotted bracket, so I couldn't access the screw head!
I realised this when after the wd40, I managed to slide out the Speedo!

As I said last night, the Speedo you have fitted now is intended for use with a 4.55 Diff.

From Stephen's image, his is intended for a 4.22 Diff.
Caveat, all this info from the Potteries website, which isn't a complete list, but is generally correct in my experience except for some of the fitment details. For example, there is a Black Face Speedo listed, with the same 1504 TPM, for a 4.55 Diff, but the list says that was for a S5 LCV.
https://potteries.mmoc.org.uk/ID/Speedo.htm

Before you go off changing the Speedo, check to see which Diff you have.

It's not worth cross checking all the options listed in the Service Part List AKD 3541, the version widely available for download doesn't even list Stephen's model, so it's not the final version.

A 1967 car *should* have a 4.22 diff, but as we don't know what else a PO did with this car, I agree it is worth checking......

[59Elva]

The chart lists different TPM values for a 4.22 diff. Different tire sizes?
If the TPM value for the 4.55 diff that was in my LCV was correct the 3.9 that I replaced it with would need 1307 TPM. I guess the 1376 or 1248 TPM are as good as I can get. About plus or minus 5%.

[svenedin]

Seeing as how the whole speedo panel is such a tight fit in the dash aperture, the side screws seem to serve little mechanical purpose.
I don't think I've ever tightened mine!
But maybe they were designed to guarantee an earth. But doesn't the speedo cable outer ensure that?.

Some are very tight, others aren’t so the securing screws are needed really.

Stephen

[geoberni]

The chart lists different TPM values for a 4.22 diff. Different tire sizes?
If the TPM value for the 4.55 diff that was in my LCV was correct the 3.9 that I replaced it with would need 1307 TPM. I guess the 1376 or 1248 TPM are as good as I can get. About plus or minus 5%.

There was a different Speedo for Radials, as highlighted.
But you look down the list and you don't get a lot of confidence in their quality control when you see comments like "(plus ****** to ****** intermittently)" and the inverted black triangle is to indicate 'Change Point unavailable' ; which makes it makes it sound as though there was a bit of 'fit anything on the shelf' at certain periods.

Speedo numbers again.JPG (125.39 KiB) Viewed 1533 times

[KevinB]

So my gold Speedo (it keeps auto capitalising this word - thinks I mean swimming trunks maybe ) has been out again to take these photos ..
.

PXL_20260827_145425979~2.jpg (1.32 MiB) Viewed 1518 times

thing with the green wires

PXL_20260827_145345661~3.jpg (1.56 MiB) Viewed 1518 times

The s/n is I think BR1305 / 00 Smith & Sons. Voltage regulator?
My fuel gauge needle moves smoothly btw - it does not jump about.

[geoberni]

BR1305 / 00 is a Smiths Voltage stabiliser, sometimes called regulator but that is really confusing when the term really applies to the device controlling the Dynamo....

The one on the minor is usually a rectangle as per the photo I posted earlier in this topic, or this one I just lifted from fleabay...
1305/00A

another stabiliser.JPG (51.96 KiB) Viewed 1495 times

No big deal so long as it's delivering a stabilised 10v.
Stephen's is a 1309/00, also a rectangular case.

There's often a caveat when trying to understand technical aspects from 60-70 years ago with limited documentation, you need to confirm the performance/outcome is what you need, and not try to 2nd guess what was happening all those decades ago.

It's likely that Smiths made slightly different models for different cars because some models of late 60s, early 70s cars had multiple gauges all requiring a 10v stabilised supply, so some will be a greater current capability than others.
Take this example diagram, where 3 instruments and their sensors each require 10v...

Typical circuit.JPG (44.59 KiB) Viewed 1495 times

.

What you could do is rig up a multimeter/voltmeter to check it is delivering 10v and not a slightly higher or lower voltage.
be aware that this thing works by opening and closing a contact several times a second, so a digital meter may flicker and an analogue meter might have the needle tremble slightly it depends on the 'quality' of the instrument.

[tomb1963]

As already stated, a modern digital multimeter will not read the voltage accurately as the voltage is switching between 12V and 0v to give an average of 10V: the voltage indicated goes all over the place as it samples many readings of either 10V or 0V. An old moving coil voltmeter such as an AVO8 may be accurate.

I replaced the component with a regulator to give a constant 10V on my 1969 Traveller so that I could fit a low fuel warning indicator with the help of other electronic trickery in order that the petrol sloshing around in the tank doesn't give false indications: and the needle on the fuel gauge does not move as the petrol sloshes around.