DDK - Die Deutschen Klassiker

My fuel gauge wouldn't indicate any levels and despite a full tank it stayed resolutely on empty.
Even the warning light was on.
It's not much fun driving around constantly expecting to grind to a halt.
It seemed likely that the VDO sender was at fault so I set about stripping it.



The end is secured by a small nut (5.5mm) and lock washer.
This was blackened and covered in muck before disassembly.



Pull open the tube to reveal the rather delicate mechanism within.
I discovered the float was doing nothing of the sort.
It was jammed solid at the base and I mean really stuck.
Everything seemed pretty clean except the bottom inch and I guess that's a legacy of nearly 20 years laid up with hardly any petrol in the tank.
The float was seized on the central shaft and took some shifiting.
Everything was gummed up like toffee (more like super glue actually).



I used penetrating oil and brute force and got the float moving.
The disc below the float needed cleaning because that's what touches when the level drops to empty.



This is the base of the unit and you can see the contacts the disc can drop down to and make the connection to activate the warning light.



You can see in this shot the very fine wires (about the thickness of a human hair). I had to clear the central shaft with abrasive paper and take care not to damage the wires.



End result... ....perfect, working gauge. Now reads true with a steady needle.
Total financial outlay = zero.

Top result!

I cleaned mine when I reconditioned my fuel tank. I had some "Marine Clean" (a POR-15 product availabled from http://www.frost.co.uk) left over. This stuff eats sticky residue without the need to brush. Highly recommended when there is a delicate wire nearby. I put the sender in a pint mug of it (diluted) and it came out looking new.

It's good knowing how much fuel you have in your car isn't it!

yep, I busted my wire when I took it apart.
new wire coming next week though. still at least I keep it topped up now.

Good post, Paul: I think I must have been lucky with my original 911 (sold last year), I just put the whole sender unit back in, and it worked fine, so never got to look inside of it.

I think I'll clean the 'new' 911's one up as you've demonstrated before recommisioning the car .

BTW, what part provides the variable resistance, is it one of the long vertical (fine) wires?

Very useful post, thanks for sharing.. It looks as if the varible resistance is provided by both the fine wires with the float connecting the cicuit.

Ferry Man wrote:

So I have taken my sender out and like Paul's it was very very dirty. I have cleaned it but in the process the thicker copper colour wire broke. So I soldered it back and was checking the connections with a voltmeter without any joy but then discovered that I am unable to get a bleep on the wire never mind the top and bottom connections! So my question is does anyone know what it's for? I have this fear that I will put it all back together and when I turn the ignition ...

I think I have figured it out. The wire is for the warning light and I am getting a signal across the connection, it just seems as the wire has a coating or something so no reading there.

I just find it scary that we are passing electricity through petrol, I take it the voltages are so small that there is not chance of a spark?

One of the wires is a Ni-chrome resistance wire which is how the float measures and if you replace this wire you will need to use a wire with very similar resistivity.

The coated wire is just a simple enamelled wire and providing the current is less than 25mA it would be safe even in a Zone 1 (Hydrogen) environment.

Good news is my gauge is working, of course being a T I don't get a warning light so the wire is redundant anyways. Only time will tell if it is giving an accurate reading.

bjmullan wrote:Good news is my gauge is working, of course being a T I don't get a warning light so the wire is redundant anyways. Only time will tell if it is giving an accurate reading.

But my car, which is the same model and vintage, does have a low fuel warning light....

Arfor.