Universal Fuel Sender Unit

I'm thinking of fitting a VDO fuel gauge. Has anyone fitted a VW Heritage universal fuel gauge sender unit to a late bay tank?
Is the hole size correct?
Is the depth correct?
Do you need to drill a series of holes for mounting?
Cheers

 

The LB sender from 73 is a 1/4 turn lock in system...

The vdo universal is a bolt in type
http://www.ebay.co.uk/itm/vdo-fuel-...arts_Vehicles_CarParts_SM&hash=item27d0f2925c

so to get it to fit a late tank will require some welding...

 

Worth checking that the sender is compatible with the gauge you're buying.

 

Thanks Paul & Snotty. If welding is required I will try persevering with the current setup.
The gauge used to only read between 0 & 2/3 full so I fitted a new sender and now it only reads between 1/3 & full.
The sender resistance range is correct so the next step is to fit a new voltage regulator but i'm not sure it will fix the problem.

 

Don't despair.

You can adjust the lever-arm senders by bending the arm - they're not gaurenteed to be right from the factory. This'll likely fix your prob with a bit of trial and error.

It's unlikely your reg is faulty. Check for pulsing on the reg output (thermo type) or a steady voltage (5-6V?) on the zener type.

 

I wish I had known that, I would of adjusted it before putting it all back together and the engine back in.

Mine reads a couple of mm over 1/4 when empty, Its not really an issue as I fill up when It gets near, just annoying

 

I don't think it's the float. I checked the gauge readings with the sender unit removed. Moved it all the way each way and the minimum reading was still 1/3 full. I tried bending the tabs to get more range and it only went down a tiny bit before going open circuit, where it suddenly drop to zero.
I'll try measuring the regulator voltage. Does the voltage change dependent on the fuel level?

I was wondering if I put an additional 10 Ohm (or maybe higher) resistance in the circuit, it might skew the whole gauge range down a bit. But I've no idea where to get suitable resistors to try it out.

I wished I'd still got the old sender unit - I could have used it in series with the new one to see if it had the desired effect.

Does anyone know if Aussie bays use the same sender units? It's an import and maybe it originally had a different sender with a higher resistance range.

 

should be the same sender... I see no reason for them being different!!

The voltage stays the same, it's actually the earth signal that changes (as the sender varies the earth resistance)

 

The regulated voltage stays the same (hence the regulation), although the mechanism is pretty crude. As Paul says, the resistance of the rheostat in the sender changes in the earth return.

You could try padding the resistance out a bit - perfectly legit - if it's going to fix the problem. Maplin'll sell you some, say, half-watt resistors, or you could buy a wire-wound preset, so you can have a twiddle.

 

Thanks Snotty.
I've had a look at the Maplins site. They don't seem to do variable restrictors but they do potentiometers. I imagine I could use just one end of one of those but they state that only go down to 50Ohms.

Would their 0.6W M10R, M11R, etc resistors be suitable?
If so I could get a few different sizes and give them a try.

 

Try a 47 ohm pot. This'll give you an idea of whether it's going to make any difference.

 

50 ohms will be its max resistance... adjusting it should make it go lower!!

 

^this. A 50 ohm pot has the range 0 - 50 ohms, according to twiddlement.

 

It's a preset potentiometer with a minimum value of 50Ohms. I'll try one of the higher rated standard ones and perhaps some fixed ones. I can't do anything for a couple of weeks but I'll let you know the results when I do.

Thanks guys. As karma is no more I shall give you a few 'likes'.

 

Some potentiometers arrived today. That are tiny. Not sure if they will take the current. Anyone know how much current flows through the fuel sender?

 

Doh! Just thought about it. I=V/R.

 

you'll be putting it in the earth circuit, so most of the current is being absorbed by the gauge anyway

 

I does indeed equal V/R . Trouble is, you don't know what the internal resistance of the gauge is (the gauge and sender will be in series, with the regulated voltage at the "top" of the chain), so it's hard to calculate the current when the sender has a value of 0ohms. The ref voltage is going to be about 6V (pulsing). You could measure the series current with a meter, with the sender in the zero-ohm position.

Personally, I'd go for, say 1W wire wound resistors, mebbe higher. You can try twiddling with the presets, then measure the resistance & swap it for a fixed resistor.

Assuming of course this mad experiment fixes your problem