Fuel Gauge/Sender mismatch?

[KevinB]

I'm not confident in my fuel gauge accuracy. The gauge is showing 1/4 but on removing the sender and looking in, the tank is pretty empty.
The ESM site says there's an early and late Speedo and fuel senders to match. Can you please help identify which speedo I have?

Photo ..

Speedometer

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[myoldjalopy]

Well, you have an earlier type speedo (gold face) with a later fuel gauge (black) previously swapped in by someone, for some reason, so will need the later sender unit to match it.

[svenedin]

Yes and dont you need an instrument voltage stabiliser for the late gauge? It runs on 10 volts.

Stephen

[KevinB]

Thank you both. A bit of a muddle then.

I have a later type sender, judging from ESM's photo. How can I find out about the voltage stabiliser?

[svenedin]

You need to pull the speedo forwards after loosening the cross head screws either side, accessible through a hole in each glovebox. The instrument voltage stabiliser is a small unit originally made by Smiths. On the later speedos it’s attached to the back near the top of the speedo.

Stephen

[KevinB]

Thank you Stephen, I shall investigate.

[geoberni]

This is what the Smiths Voltage Stabiliser looks like, you can't miss it.
.

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.
However I doubt you'll find it on the Speedometer, as the Speedo it fits doesn't have a lamp in the top position like yours does.
So there's nowhere for it to go, unless they loosened off one of the two bolts that actually holds the speedo in it's casing.

If the culprit who fitted the Black Fuel Gauge didn't know/care about the Voltage Stabiliser, they might have omitted it.
But they could equally have just left it laying loose, or bolted it elsewhere.

[KevinB]

Thank you geoberni. Now I know what I'm looking for. I'm finding it beastly to get any access behind there.
I have managed to remove the 9 o'clock screw, but the 3 o'clock is covered by some metal bracketry. I will have to try to feel if the regulator is there, but as you say, it may well not be.

[Bill_qaz]

No need to fully remove the speedo mounting screws as the bracket is slotted, just slacken and pull speedo out of dash.

[KevinB]

Thanks Bill, but I can't get any access yet to the screw head. So unless it's a bit loose ...

[Mervin]

Will that speedo be correct for the car? i.e. serial number and turns per mile. Which could affect it's accuracy.
My car is early 1962 and has a 1098cc engine and ribbed gearbox which replaced the original 948cc engine and gearbox. The differential is still original as will be the ratio.
My speedometer has the same serial number and t.p.m. as that pictured in Kevin's car.

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[myoldjalopy]

Thank you geoberni. Now I know what I'm looking for. I'm finding it beastly to get any access behind there.
I have managed to remove the 9 o'clock screw, but the 3 o'clock is covered by some metal bracketry. I will have to try to feel if the regulator is there, but as you say, it may well not be.

This should be straightforward, but I don't understand why the second screw is "covered by some metal bracketry". It should be a mirror image of the side where you have already removed the screw (but, yes, it only needs to be slackened off). Could it even be missing? If it comes to the worst, you may have to remove that glove box liner to see what's going on properly....

[KevinB]

Thanks myoldjalopy, the gloves box liner is out already. And so is ... the Speedo! A bit of wd40, brute finger force and it popped out.

What's the verdict? Better than expected?

PS thanks Mervin

[ManyMinors]

People seem to be missing the point that it is probably the speedo that is incorrect in your car rather than the fuel gauge?
It would probably be easier to simply acquire the correct speedo and then everything should be well?
That is what I would do in your position

[svenedin]

The verdict is you don't have an instrument voltage stabiliser.

The older speedos did not use an instrument voltage stabiliser for the fuel gauge. They use a gauge that reads instantly when the ignition is switched on and the needle can change rapidly when the petrol sloshes around inside the tank.

The later, black-dial speedos use a black-dial petrol gauge in conjunction with an instrument voltage stabiliser and a different sender in the fuel tank. That set up has the fuel gauge creep up slowly when the ignition is turned on which is the instrument voltage stabiliser warming up (it uses a bimetallic strip thermal vibrator to produce an "average" 10 volts). These gauge needles do not jump around when the car is driven.

So you have an earlier speedo with a later fuel gauge and a later sender. It will not read correctly because it needs 10 volts.

I think the best thing to do is fit the right petrol gauge and sender having checked it is the correct TPM speedo first.

Or you can fit an instrument voltage stabiliser which will need some wires moved around. I am not sure how you would mount it on the earlier speedo as I wasn't designed to have one.

Stephen

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[myoldjalopy]

People seem to be missing the point that it is probably the speedo that is incorrect in your car rather than the fuel gauge?
It would probably be easier to simply acquire the correct speedo and then everything should be well?
That is what I would do in your position

Yes, of course this is correct. A 1967 car would have had one of the black speedo's. What we don't know is why someone previously swapped in a gold-face speedo but retained the black gauge - and what else they may have done/not done.
Assuming all else with the car's drive train is standard for 1967, then I would certainly consider ManyMinor's advice. Otherwise, as Stephen suggests, if it is the correct TMP speedo, then fit the correct gold gauge and sender unit.

[geoberni]

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.

The verdict is you don't have an instrument voltage stabiliser.

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.

[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.

The verdict is you don't have an instrument voltage stabiliser.

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

[Bill_qaz]

You also have a section of exposed wire core that needs insulating

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[geoberni]

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.

The verdict is you don't have an instrument voltage stabiliser.

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.