1974 SB Fuel Gauge

[LeeFred]

The fuel gauge on our 74 Super has always acted wonky but lately it hasn't been working at all. I've read some threads on things to check and do regarding the fuel gauge and fuel sender, so I'm getting ready to dive in.

My question is, does the fuel gauge actually need the "vibrator" that operates it, or can another regulator that goes from 12V to 5V work also? I ask because I come from working on 1st generation Mustangs and have a 1965 that I work on. The gauges on it have a constant voltage regulator (CVR) that does the same thing that the vibrator does. I have a handful of CVRs in my Mustang stash of parts and wonder if one of those would work instead of having to order and wait for the vibrator if that turns out to be the issue?

I use a more modern CVR in the Mustang with modern electronics and it works quite well for me.

[rdwood]

I used an adjustable LM317 voltage regulator in place of the vibrator because I needed a little higher voltage output to get my gauge needle to show Full when the tank sensor was reading 10 ohms. Has been working well for over a year for me. I'll post some pics of my setup.
_________________
'57 Beetle- Horizon Blue
'71 Ghia Convertible - Tornado Red
'74 Super Beetle - Tropical Green

[Blue69Baja]

With the aftermarket gauge, which has a higher resistance, <>32 ohms and the OEM gauge is at <>18 the higher voltage is needed like RDWOOD says. The voltage needed is around 6.4volts and needs to be steady when your battery voltage at the fuse block is below 12v and up to 14.x volts!

I did some work on the fuel gauge project and ended up using buck regulators. After some renditions of regulation I settled on this design, shown in a link below.

I have a few running in some fellas cars with the aftermarket gauges and the regulator set for 6.4 and it has worked quite well.
A regulator circuit like RDWOOD did will work good too. Obtaining the proper components is difficult since Radio Shack has shut down.

The Super Beetle aftermarket senders are not very good or accurate. There is one mfg that makes a good one.. It is made in Mexico.
There are other sources for the Mex sender besides the one in my link.

https://vwparts.aircooled.net/Fuel-Tank-Sending-Unit-MX-or-B-All-Super-Beetle-p/113-919-051fmebr.htm

My Vw channel is for information only, not professionally done. I provided information to the Gauge MFG and distributors via the various videos. I wanted them to resolve the gauge issue but they have not done anything and that has been almost 4 years now.

Here is a video of the proof of the 6.4 volts working on several gauges.

I am not mfg nor selling any of my product.

https://youtu.be/bFIukoNi_8w?si=H99Hj0YQHR5p7EEN

Jim.
_________________
69 Baja with a 1914...
72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original..

[rdwood]

I bought the cheap regulator (4 pak) already built from a supplier on Amazon. You have to be careful as the heatsink for the new regulator does not go to ground. I wanted to use the same mounting screw on the speedo so I have a plastic spacer to insulate the screw (which is car ground) from my aluminum heatsink.
_________________
'57 Beetle- Horizon Blue
'71 Ghia Convertible - Tornado Red
'74 Super Beetle - Tropical Green

[rdwood]

I am still using the original gauge and OEM tank sensor but still needed a little higher voltage than what the old vibrator was putting out. I think I set mine to 5.6 volts.

I tested this on a bench with the gauge, new regulator circuit and a resistor decade box to simulate the tank sensor, then adjusted the regulator voltage until I was reading Full on the gauge when the resistor decade box was set to 10 ohms.

At 85 ohms the gauge will show empty.

This looks like the circuit I bought. 6pk now. I removed the bulky screw terminal blocks on each end and soldered my own wires and connectors directly to the circuit board.
https://www.amazon.com/DIANN-Converter-Circuit-Adj...mp;sr=8-11
_________________
'57 Beetle- Horizon Blue
'71 Ghia Convertible - Tornado Red
'74 Super Beetle - Tropical Green

[Blue69Baja]

[Blue69Baja]

Redwood, when you got the regulator circuit was it set for full voltage around 12v or for low voltage <> 9?
Presume that the Pot is a 20 turn?

If set to 12 and someone was to install it then it will fry the gauge and possibly the sender!

Just curious.

Maybe you could do a video doing the set up for the LM reg module.

I could do it too If you ok it.

Thanks,

Jim.
_________________
69 Baja with a 1914...
72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original..

[rdwood]

Jim, Thanks for the compliment and for uploading the helpful videos to You Tube.

I knew from previously measuring the output of the original vibrator that the DC voltage should be around 5.3 volts so I preset my LM317 to that voltage before connecting it to the other components. I then started adjusting slowly and watching the reaction on the gas gauge.
_________________
'57 Beetle- Horizon Blue
'71 Ghia Convertible - Tornado Red
'74 Super Beetle - Tropical Green

[rdwood]

Jim,
Since this was over a year ago when I did this, a lot of the details have escaped my old mind. I can't recall the limitations now with using the LM317 and setting it up. If you want to give it a go, I'm sure that would be beneficial to a lot of folks frustrated with these gas gauges.
_________________
'57 Beetle- Horizon Blue
'71 Ghia Convertible - Tornado Red
'74 Super Beetle - Tropical Green

[LeeFred]

Lots of good info on here, and thanks. Now I know what direction to go and nice to know I'm not stuck having to use an OEM-type vibrator to get the gauge functioning somewhat properly.

[Blue69Baja]

Redwood, have you measured the output of the Lm regulator with the input voltage going from around 12.3 to around 14v, kind of like the voltage in a VW. This is a 13% deviation.

I would imagine that the output of the LM module is going to vary about .8v.
I will get this Lm regulator module and test it to see what the difference in gauge reading will be produced. Might take me a month or two.. I am very busy most of the time.

I know that if you put the aftermarket gauge with the vibrator or the aftermarket plastic regulator the gauge will read about 1/2 tank when actually full.
Most guys deal with the situation and when the gauge shows R it is pretty close to accurate.

I just like to see the gauge go to full when the tank is full hahahaaa.
_________________
69 Baja with a 1914...
72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original..

[Blue69Baja]

Since I am ordering the LM module I am also ordering one of these.
It is a buck regulator, all water proof and adjustable. Does not have a gauge like the Bucks I show in my videos.
The Buck regulators maintain the output set voltage even if the input voltage goes below 10v or over 30vdc... This is the reason I ended up with the buck regulator as my finished design.

https://www.amazon.com/dp/B00C0KL1OM?ref=ppx_yo2ov_dt_b_product_details&th=1

Jim.
_________________
69 Baja with a 1914...
72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original..

[rdwood]

Jim,
Please update this post as you make progress with your setup and testing.

I have no experience with the aftermarket gauge and vibrator but I have heard that they can't be intermixed with the original components since their internal resistances, as you have pointed out, are different.

The OEM and aftermarket tank sensors should work fine with either setup as long as, a first step, they measure around 10 ohms when the tank is "Full".

Randy
_________________
'57 Beetle- Horizon Blue
'71 Ghia Convertible - Tornado Red
'74 Super Beetle - Tropical Green

[Blue69Baja]

[Blue69Baja]

I received the Lm 317 regulator module.

Here is a brief summary. I will present more in the next week or so.

Set up.
I provided 13volts into the LM module and set the output to 6.4vdc. No output load.
Testing parameters.
1. Vary the input to the Lm module and verify the LM module output voltage drift.
2. Measure the temperature of the LM317 regulator.

Findings:

1. I varied the input voltage from 8vdc to 15vdc. I verified that there was no drift or change in the output of the LM module. The output was stable.
2. The temperature of the LM 317 was steady at <>100deg. This is with no output load.. Meaning no gauge nor sender. No output connection.

3 Attached an aftermarket gauge and the proper resistors to make the gauge show E, R, 1/4, 1/2 and Full ....
All readings on 2 gauges read sufficiently/good

4. The temperature of the LM317 transistor when the load of the output of the module was set to make the gauge show full... 10 ohms.
This would be the biggest load.
The temp of the LM317 reached 134 deg F. Satisfactory. It has temperature compensation, which we would never reach... The compensation starts at about 125c.. HOT!

What is the maximum temperature of LM317?
The LM317 can go to a junction temperature of over 100°C without failure. If it gets too hot it will automatically reduce the current to limit any further heat build-up.

Conclusion:

The LM module will work excellently for our application.



Requirement. Initial...
1. bench set up is needed. Hook to a 9- 30 volt source on the input.
Using a dvm set the output voltage for 6.4vdc.

2. Obtain the proper terminal 1/4" lugs and wires to make leads to connect to the VW wiring.

Notes:
I would fuse the input 12 from the vehicle with a small value fuse. 1-2 amps... I would also put a 7.5 zener diode across the output of the LM 317. This provides over voltage protection for you gauge and sender if the LM module malfunctioned and put over 7.5 volts on the output due to a failure of the Lm317 and the output goes up! The Zener diode will short due to over voltage, that in turn will make the regulator's current to spike and will pop the little fuse thus protecting wiring, gauge and sender.

In the near future I will do a video of how to do the fusing, protection and wiring.

Here is a link to pictures of the testing of two gauges. You will see that the needle is not exactly in position v/s the resistance I attached. It is just a difference between gauges. Nothing we can do about that.
One other thing... The needle moves very slow unlike the way an OEM vibrator and gauge works! That is another story.

Gauge 01 link, sorry I do not have them in order to fuel level..

https://photos.app.goo.gl/ysP2DczEhv8gPBoaA


Gauge 02 link....

https://photos.app.goo.gl/ysP2DczEhv8gPBoaA

Jim.
_________________
69 Baja with a 1914...
72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original..

[rdwood]

Hi Jim, thanks for the update on your findings.

I would add that this regulator is also useful with the OEM gauge and OEM sender. In my case, the original gauge wouldn't read full scale when the sender (or using a resistor) had a resistance of 10 ohms. I concluded that the internal resistance of my gauge must have increased above nominal. (I admit I never measured my gauge resistance)

To compensate for that, I decided to use this regulator to increase the circuit voltage above what the vibrator normally is set to, until the gauge read Full scale with a 10 ohm load. I believe that was around 5.6V. This is working well for me.
_________________
'57 Beetle- Horizon Blue
'71 Ghia Convertible - Tornado Red
'74 Super Beetle - Tropical Green

[Blue69Baja]

[Blue69Baja]

Well my fuel gauge project is finished...hahahaa. After 5 years of frustration from the Super Beetle fuel tank, Sender, Fuel gauge resistance issue and the vibrator I feel that we have a solution that works

I want to thank Rdwood for finding a nice adjustable regulator that works quite well!

Here is a video of how to wire up the LM317 module to make it work in all VW's with electronic fuel gauges. Type 1, 2 ,3 and the Thing too!

There are two Regulators in the video. I like the buck regulator because it is weather proof.


Link


Jim
_________________
69 Baja with a 1914...
72 Super 100% orig...W/ factory air... 56,000mi
Even the spare is original..

[vamram]

RDWood & Jim - thanks for putting this together, excellent work, much appreciated. My '74's gauge no longer goes to Full when the tank is full, so I may be venturing into this very repair soon.

Jim - any chance you can post a picture of the gauge fully assembled on the speedo?

Thanks!
_________________
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'74 Super 9/16 - present, in refurb process.
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[Blue69Baja]