TheSamba.com :: View topic - help with vdo fuel gauge

Tue Jun 16, 2009 8:06 am

I have a fuel gauge similar to that shown in tech bulletin http://www.thesamba.com/vw/archives/manuals/techbulletins/k8/9_58_page1.jpg. Problem is, when the fuel tank is full the gauge reads only about 8 on a scale of 1-10, and the tank is still nearly half full when the gauge reads zero. Otherwise, the gauge seems to give a pretty good indication of how much fuel is in the tank from full to half full.

I know virtually nothing about these gauges despite having searched the forums and 'net for info. Can anyone here with some experience of these gauges give me some advice.

I've cleaned up all the wires & contacts from the sender unit to the gauge, by the way.

Tue Jun 16, 2009 11:42 am

Sounds like you have the wrong, or bad sender. You did hook it up correctly right? Ground portion goes to sender, not 12v.

I'm not sure if there is a calibration procedure for that gauge. Lemme look.

Tue Jun 16, 2009 11:54 am

I would start by taking the sender out. Use a VOM to test the resistance.

Hook one lead to the spade connector, the other to the metal body of the sender. The resistance range should be from 78 Ohm to 0 Ohm.

Manually actuate the float and watch the readings. To high of a reading tells you the sender is either bad, or the incorrect one for the gauge.

If the reading is high, you could always add a small resistor in line with the ground wire.

***Edit... High meaning high ohm reading...IE 85+ ohms. Not 0 Ohm shorted.

Wed Jun 17, 2009 9:47 pm

Thanks for the suggestion. I'll go take a look and let you know the results.

Thu Jun 18, 2009 8:51 am

What year is this on? And the accessory gauges used different tank sending units than later stock electric gauges. Do you know if yours match?

Thu Jun 18, 2009 8:52 am

If your sending unit is defective, you can purchase a VDO adjustable sending unit to work with that gauge from N. Hollywood Speedometer.

Thu Jun 18, 2009 9:31 am

^^^ Yup.

I'm betting that he has a setup stolen out of a 66+ Ghia. If that's the case, I think the float and tank are a bit different.

Thu Jun 18, 2009 10:28 am

Does a ghia have a different gas tank than a bug? I've heard you can swap the mechanical gauge in a bug with the electronic one in a ghia, or am I just wrong?

Thu Jun 18, 2009 10:37 am

Ghia tanks were the same. Ghias however used different tank sending units and fuel gauges than bugs, well, except for 1973-74. I took the guts out of a late 60s Ghia/type 3 style gauge and put them into an Bug accessory gauge once, and used it with a Ghia tank unit. It worked, the calibration marks were not quite the same but it worked.

Thu Jun 18, 2009 10:42 am

glutamodo wrote: Ghia tanks were the same.

I always thought early Ghia's had a different shaped "Bulge" in the bottom of the tank for tie rod clearance... Or am I just high? :lol:

Thu Jun 18, 2009 10:48 am

Ah, I'm not sure about underneath, was mostly thinking about when they got transplanted into bugs so they could have the fuel guage that was only on ghia tanks on 61/older.

Fri Jan 23, 2015 7:25 pm

72 ghia convertible
After replacing my speedometer with one from a superbeetl, I found the gauge was dead. I bought a replacement gauge (ebay) and installed it.
PROBLEM: Readings tend to be high
I've re-bent the sender lever and bent the tab that blocks the lever from dropping too far....but the gauge never reads less than halfway down the Reserve. I tried adjusting the calibration gear on the gauge also.
Sender is a VDO with one lead.
Any sugstions to allow true zeroing?
Adding a resistor?
Thanks

Fri Jan 23, 2015 10:00 pm

The gauge on the '72 DID NOThave a vibrator. This gauge does. My understanding is that the "vibrator" is a capacitor. It doesn't seem likely but,cCould the presence of a vibrator paired with a newer sender cause the higher readings?

Sat Jan 24, 2015 5:40 pm

Not sure what you have going on there with all the parts swapping and such, but will offer some info for thought.

-I believe the "vibrator" is more of a voltage stabilizer so that the gauge is not effected by sudden voltage changes that could make the needle swing one way or the other erroneously.
It's there so when the charging system surges from say 11 volts to 14 volts it's output to the gauge remains at a steady voltage (IIRC only about 9 to 10 volts).

-The gauge is supplied with a steady voltage, and the sender provides a variable ground.

-If you disconnect the sender wire and leave it loose, the gauge should read empty.

-Conversely, if you ground the sender wire the gauge should read full.

So, not sure what your fix is either, but your thinking is along the right line.
More resistance in the sender leg of the circuit, or perhaps less voltage going to the gauge.

You might find more help in the Late Model forums where the cars have electric fuel gauges. Found this link there, might be helpful...
http://www.speedyjim.net/htm/fuel_ga.htm